Instabilidad ng Balikat Impormasyon In-depth

This is the clinical evidence summary written for health professionals. It is technical, and it lists the research this page was built from. You do not need to read it to understand your treatment or to make a decision about it.

Overview

Epidemiology and Cohorts

• The MOON Shoulder Instability Study has enrolled the largest cohort of patients undergoing shoulder stabilization to date [3].
• A review evaluates existing data on the presentation of shoulder instability in men and women to determine if there are differences in occurrence, treatment, or functional outcome following management [8].

Nonoperative Management

• At long-term follow-up of 17 years, a high rate of poor outcomes was observed following nonoperative management of anterior shoulder instability [4].
• Most patients younger than 40 years with shoulder instability who were initially treated nonoperatively for 6 months were definitively treated without surgery [6].
• Long-term follow-up demonstrates that nearly 40% of patients treated non-operatively for posterior shoulder instability eventually require surgery [9].

Operative Management

• Surgical treatment of primary, traumatic, anterior shoulder instability results in reduced rates of recurrence compared with nonsurgical treatment at 10-year follow-up [17].
• The 1-year outcomes in a prospective study suggest superiority of operative over non-operative treatment for posterior shoulder instability [14].
• The early and midterm results of arthroscopic stabilization of the shoulder for posterior instability are promising [20].
• Arthroscopic capsulolabral repair for posterior shoulder instability was a durable treatment option that improved long-term shoulder pain and function and facilitated return to sport in the majority of patients at a mean follow-up of 15.4 years, although a notable proportion of patients met various criteria for failure [84].
• The Bristow-Latarjet procedure was associated with significantly higher rates of full return to sport than Bankart repairs in anterior shoulder instability, despite variability in patient indications across procedures [212].
• Free bone block procedures are considered safe and clinically effective for the management of anterior shoulder instability with glenoid bone loss [24].
• In carefully selected patients, the use of anterior and posterior glenoid bone augmentation may be effective as a salvage procedure in rare cases of refractory multidirectional shoulder instability [219].

Indications and Evaluation

• Proper evaluation of bone loss best determines shoulder instability surgical indications and outcomes [11].
• The indications for an isolated soft-tissue procedure in anterior shoulder instability are now narrower; the ideal candidate presents with minimal glenoid bone loss (13.5%) [61].
• Failure of primary shoulder stabilization procedures is often related to uncorrected anatomic pathology, and the instability severity index score permits precise identification of patients at risk [12].
• In the interim, surgical soft-tissue stabilization might be more aggressively indicated in cases of primary shoulder dislocation, whereas recurrent instability with bone loss should be referred to experienced high-volume specialists [82].

Revision and Salvage

• The short-term outcome in a small series of arthroscopic revision surgery in shoulder instability is challenging and encouraging [21].
• Arthroscopic management of a failed instability repair provides similar success to open reconstruction if one selects proper indications [194].

Outcomes and Measurement

• The consensus statement aims to improve diagnosis and treatment of shoulder instability through universal agreement on outcome measurement tools and tailored treatment based on pathology, patient age, activity demands, and surgeon skills [23].
• The French version of the Western Ontario Shoulder Instability Index (WOSI-Fr) is recommended for following up patients with shoulder instability [36].
• The thresholds defined in a 2025 study can provide a guideline for interpreting patient outcomes following arthroscopic stabilization for posterior shoulder instability, allowing for earlier detection of recurrent posterior instability [58].
• Despite the wide array of available patient-reported outcome measures for assessing shoulder instability surgery outcomes, the availability of clinically significant outcome thresholds such as MCID and PASS remains relatively limited [196].
• The authors of a 2018 study express caution regarding the consensus that the WOSI should be used as the primary outcome measure for all studies on the treatment of shoulder instability before further prospective, high-level, evidence-based studies and multi-center studies are performed [213].
• Randomized controlled trials reporting on shoulder instability surgery are well performed but poorly reported [64].

Anatomy & Pathophysiology

Bony Anatomy

• The glenohumeral joint is inherently predisposed to instability by its bony architecture [86].
• The glenoid cavity is a shallow socket, approximately one third the size of the humeral head [96].
• The bony anatomy contributes little to stability and has been compared with a golf ball on a tee [105].
• The glenoid is a convex structure of shallow depth shaped like an inverted pear [95].
• The subchondral bone of the glenoid is relatively flat, with the articular concavity augmented by cartilage and a circumferential labrum [97].
• The glenoid averages 5° of retroversion in relation to the axis of the scapular body [97].
• The humeral head averages 19° of retroversion and 41° of inclination (neck-shaft angle) [97].
• The humeral head is retroverted an average of 30 degrees relative to the transepicondylar axis of the humerus [96].
• The articular surface of the humeral head is essentially spherical, with an arc of approximately 160 degrees covered by articular cartilage [104].
• The radius of curvature of the humeral head is approximately 25 mm and is slightly larger in men than in women [104].
• The glenoid articular surface radius of curvature is 2 to 3 mm larger than that of the humeral head [104].
• The average neck-shaft angle is 45 degrees (±5 degrees), with a range of 30 to 50 degrees [104].
• The superior margin of the humeral head articular surface normally is superior to the top of the greater tuberosity by 8 to 10 mm [104].
• The distance from the lateral base of the coracoid process to the lateral margin of the greater tuberosity is called the lateral humeral offset [104].
• A significant decrease in lateral humeral offset reduces the lever arms for the deltoid and supraspinatus muscles, which weakens abduction and impairs function [104].
• A significant increase in lateral humeral offset causes excessive tension on the soft tissues ("overstuffing" of the joint), which results in loss of motion and likely accelerates polyethylene wear [104].
• Proximal humeral retroversion is highly variable, ranging from 0 to 55 degrees, depending on the method used for measurement [104].
• The glenoid diameter ranges from 18-30 mm superior anteroposteriorly and 21-35 mm inferior anteroposteriorly [104].
• The glenoid inclination averages 4.2 degrees (range –7 to 20 degrees) [104].
• The glenoid version averages 1.5 degrees retroversion (range 10.5-9.5 degrees anteversion) [104].
• The glenoid surface area is 4-6 mm and the humeral head surface area is 11-19 mm [104].
• The glenoid cartilage thickness is 2.16 mm and the humeral head cartilage thickness is 1.44 mm [104].
• The glenoid radius of curvature is 22-28 mm and the humeral head radius of curvature is 23-28 mm [104].
• The medial (coronal) humeral offset is 4-14 mm and the posterior (transverse) humeral offset is –2 to 10 mm [104].
• The scapula spans the second through seventh ribs and serves as an attachment for 17 muscles [106].
• The scapula is anteverted on the chest wall approximately 30 degrees relative to the body [106].
• The glenoid is retroverted approximately 5 degrees relative to the scapular body [106].
• The humeral head is retroverted 30 degrees relative to the transepicondylar axis of the humerus [106].
• The head height is approximately 5.6 cm above the superior border of the pectoralis major tendon [106].
• The anatomic neck is located directly below the humeral head and serves as an attachment for the shoulder capsule [106].
• The surgical neck is more distal than the anatomic neck and is more often involved in fractures [106].
• The transverse humeral ligament is an important stabilizer of the biceps tendon [106].
• The coracoacromial ligament contributes to anterosuperior stability in rotator cuff deficiency and should be preserved with irreparable cuff tears to prevent anterosuperior escape [106].
• The acromial branch of the thoracoacromial artery runs on the medial aspect of the coracoacromial ligament [106].
• The coracoacromial ligament is the arthroscopic landmark for a complete release of the rotator interval for adhesive capsulitis [106].
• The clavicle is the first bone in the body to ossify at 5 weeks gestation and the last to fuse with the medial epiphysis fusing at 25 years of age [106].
• Fracture of the clavicle is the most common musculoskeletal birth injury [106].
• The proximal humerus has three ossification centers: the humeral head (4 to 6 months), the greater tuberosity (1 to 3 years), and the lesser tuberosity (3 to 5 years) [97].
• The proximal humeral ossification centers fuse to the shaft at age 17 to 20 years [97].
• The anterolateral ascending branch of the anterior humeral circumflex artery provides the primary blood supply to the humeral head [97].
• The terminal intraosseous portion of the anterior humeral circumflex artery enters at the proximal aspect of the intertubercular groove as the arcuate artery [97].
• The proximal humerus is primarily cartilaginous at birth, with ossification centers detectable by ultrasonography as early as the 38th week of gestation [101].
• The ossification center for the humeral head is usually present at birth [101].
• The greater tuberosity ossification center appears by 1 to 3 years of age [101].
• The lesser tuberosity ossification center appears by 5 years of age [101].
• The proximal humeral ossification centers fuse by 5 to 7 years of age to form the humeral head [101].
• The proximal humeral physis closes by 14 to 17 years of age in girls and by 16 to 18 years in boys [101].
• Humeral retroversion averages 65 degrees in infants and young children and gradually decreases, approaching adult values by 11 years of age [101].
• Eighty percent of subsequent humeral growth comes from the proximal humeral physis, accounting for approximately 40% of the growth of the entire upper extremity [101].
• Less than 75% of humeral growth occurs before 2 years of age and more than 85% occurs by 8 years of age [101].
• The capsule of the glenohumeral joint extends from the glenoid rim, progressing laterally toward the surgical neck of the humerus and blending with the tendons of the rotator cuff musculature [101].
• The posteromedial metaphysis, a portion of the physis, and the epiphysis are intracapsular [101].
• A large part of the proximal humeral physis is extracapsular, making it susceptible to traumatic injury [101].
• The proximal humeral physis is irregularly shaped, with its apex located on the posteromedial portion of the proximal humerus [101].
• The periosteum is thicker and stronger in the posteromedial portion of the proximal humerus as opposed to the anterolateral portion, which is often quite thin [101].
• The subscapularis originates from the anterior scapula and inserts anteriorly onto the lesser tuberosity [101].
• The greater tuberosity provides attachment superiorly and posteriorly for the supraspinatus, infraspinatus, and teres minor [101].
• The deltoid forward flexes and abducts the shoulder and courses from the clavicle and acromion superiorly, coalescing into a common tendinous insertion onto the lateral upper third of the humeral shaft [101].
• The pectoralis major powers adduction and internal rotation due to its tendinous insertion anteriorly onto the lateral wall of the bicipital groove [101].
• The pectoralis major forms the roof of the distal continuation of the bicipital tunnel, which is a closed space that extends proximally to the glenohumeral joint [101].
• The anterior and posterior humeral circumflex arteries provide a rich blood supply to the proximal humerus [101].
• 64% of the humeral head blood supply arises from the posterior humeral circumflex artery [101].
• The brachial plexus is prone to injury when the proximal humerus is injured in fractures or dislocations, or during traction [101].
• The axillary nerve circles the humeral neck just inferior to the glenohumeral joint as it courses posteriorly [101].
• The scapula in humans is suspended by muscles alone and has shifted caudally from the cervical position in lower animals [102].
• The scapular index is extremely high in pronograde animals with a long, narrow scapula [102].
• The scapula is broader in humans and other primates, with the most pronounced differences observed in the infraspinatus fossa [102].
• Broadening of the infraspinatus fossa has resulted in a change in the vector of muscle pull from the axillary border of the scapula to the glenoid fossa [102].
• This adaptation allows the infraspinatus and teres minor muscles to be more effective in their roles as depressors and external rotators of the humeral head [102].
• The supraspinatus fossa and muscle have changed little in size or shape over time [102].
• The acromion has enlarged over time, reflecting the increasing role of the deltoid muscle in shoulder function [102].
• The broader attachment of the deltoid on the acromion and its more distal insertion on the humerus have increased its mechanical advantage in shoulder motion [102].
• The coracoid process has undergone an increase in size over time [102].
• With the shoulder in 90 degrees of abduction, the coracoid extension over the glenohumeral joint can mechanically limit anterior translation of the humerus relative to the glenoid [102].
• One shoulder tested after sectioning the capsule would not dislocate anteriorly in full abduction until the coracoid process was removed [102].
• The anteroposterior dimension of the thoracic cage decreased over time, resulting in the scapula positioned approximately 45 degrees to the midline [102].
• The scapula and glenoid fossa assumed a more dorsal position in the thoracic cage, which led to the glenoid fossa being directed laterally [102].
• Consequently, a relative external rotation of the humeral head and an internal rotation of the shaft occurred [102].
• The size of the infraspinatus fossa gradually enlarged over time relative to the length of the scapular spine [102].
• This relative increase has led to a decrease in the scapular index [102].

Soft Tissue Anatomy & Stabilizers

• The glenohumeral joint depends on static and dynamic stabilizers for movement and stability [104].
• The rotator cuff stabilizes the glenohumeral joint while allowing greater freedom of motion [104].
• The rotator cuff fixes the fulcrum of the upper extremity against which the deltoid can contract and elevate the humerus [104].
• The rotator cuff must act simultaneously and synergistically with the deltoid muscle for normal function [104].
• The shoulder joint is composed of four articulations: the sternoclavicular, acromioclavicular, glenohumeral, and scapulothoracic [105].
• These articulations work together to allow the shoulder joint to have the greatest range of motion of any joint in the body [105].
• Normal function of the shoulder is a balance between mobility and stability [105].
• Mobility is allowed by the "large ball–small socket" bony arrangement and the voluminous glenohumeral joint capsule, which does not restrict movement until the extremes of motion [105].
• The glenoid is encircled by the labrum, composed of dense fibrocartilaginous tissue, which increases the depth of the socket by 50% around the humeral head and increases stability [105].
• The glenoid articular surface and the labrum combine to create a socket that is approximately 9 mm deep in the superoinferior direction and 5 mm deep in the anteroposterior direction [105].
• Adding the glenoid labrum increases the glenoid surface to 75% of the humeral head vertically and 57% horizontally [105].
• Biomechanical testing of cadaver shoulder specimens showed that the labrum affects the distribution of contact stresses when a compressive load is applied to the shoulder at 90 degrees of abduction [105].
• Because there is very little bony constraint to the shoulder, most of the stability is provided by the surrounding muscles and ligaments [105].
• The ligamentous constraints are the primary stabilizers at extremes of motion [105].
• The superior glenohumeral ligament is the primary restraint to inferior humeral subluxation in 0 degrees of abduction [105].
• The superior glenohumeral ligament is the primary stabilizer to anterior and posterior stress in 0 degrees of abduction [105].
• Tightening of the rotator interval, which includes the superior glenohumeral ligament, decreases posterior and inferior translation [105].
• The middle glenohumeral ligament limits external rotation when the arm is in the lower and middle ranges of abduction but has little effect when the arm is in 90 degrees of abduction [105].
• The inferior glenohumeral ligament is composed of an anterior band that is quite thick, a posterior band that is less thick and distinct, and a thinner intervening axillary pouch, creating a hammock-type sling [105].
• With external rotation, the hammock slides anteriorly and superiorly, the anterior band tightens, and the posterior band fans out [105].
• With internal rotation, the opposite occurs to the inferior glenohumeral ligament hammock [105].
• The anteroinferior glenohumeral ligament complex is the main stabilizer to anterior and posterior stresses when the shoulder is abducted 45 degrees or more [105].
• The extrinsic muscles primarily control movement of the scapula and include the rhomboids, levator scapulae, trapezius, and serratus anterior [105].
• The intrinsic muscles control the glenohumeral joint and include the rotator cuff muscles (subscapularis, supraspinatus, infraspinatus, and teres minor), the deltoid, the pectoralis major, the teres major, the latissimus dorsi, and the biceps brachii [105].
• The extrinsic muscles dynamically position the scapula to place the glenoid opposite the humeral head as the shoulder moves [105].
• Rowe compared the relationship of scapular positioning to a "ball on a seal’s nose" [105].
• Ligament stiffness and torsional rigidity are increased with concomitant muscle activity [105].
• Rotator cuff activity and biceps activity have been shown to stiffen the capsule and decrease glenohumeral translation [105].
• Intrinsic and extrinsic muscles serve as fine tuners of motion and power movers by working in "force couples" [105].
• The force couples control and direct the force through the joint, contributing to stability [105].
• The most important force couple involves the subscapularis and posterior rotator cuff [105].
• Together, the subscapularis and posterior rotator cuff provide a compressive force that centers the humeral head in the glenoid cavity [105].
• The teres minor has often been viewed as a minor contributor to rotator cuff function, but there has been heightened attention to its contribution, particularly when the other cuff tendons fail [105].
• The tendinous insertions of the rotator cuff muscles, the articular capsule, the coracohumeral ligament, and the glenohumeral ligament complex blend into a confluent sheet before insertion into the humeral tuberosities [105].
• The tendons of the infraspinatus and supraspinatus muscles join approximately 15 mm proximal to their insertion and cannot be readily separated by blunt dissection [105].
• The infraspinatus and teres minor fuse near their musculotendinous junctions [105].
• The supraspinatus and subscapularis tendons join as a sheath that surrounds the biceps tendon at the entrance of the

Classification

• Shoulder instability presents with a variety of clinical presentations and has historically been poorly understood due to its complex nature [1].
• The aetiologies and clinical manifestations of non-traumatic shoulder instability are multifactorial [2].
• The Multicenter Orthopaedic Outcomes Network (MOON) Shoulder Group was formed to conduct large multicenter studies on conditions of the shoulder [5].
• The MOON Shoulder Group consists of 16 fellowship-trained orthopaedic surgeons and research personnel from nine academic and private practice sites in the United States [5].
• MOON Shoulder Instability is an offshoot of MOON Shoulder that focuses on patients undergoing surgical treatment for shoulder instability [5].
• Existing data on the presentation of shoulder instability in men and women are evaluated to determine if there are differences in occurrence, treatment, or functional outcome following management [8].
• Biomechanical studies on posterior shoulder instability remain limited in the literature, with current models performed in a static manner which limits their translation for explaining a dynamic pathology [10].
• Failure of primary shoulder stabilization procedures is often related to uncorrected anatomic pathology [12].
• The instability severity index score permits precise identification of patients at risk for failure of primary shoulder stabilization procedures [12].
• As knowledge of the basic science behind the pathophysiology of shoulder instability improves and more clinical reports emerge, the exact indications for arthroscopic stabilization are gradually being refined [13].
• Significant advances in identifying the pathologic etiology of the unstable shoulder have occurred because of basic science glenohumeral ligament cutting studies, clinical evaluation, and the advent of arthroscopic evaluation and treatment [15].
• Anatomical variants should not be confounded with pathological findings when evaluating shoulder instability [16].
• Different anatomical lesions can be found depending on the type of instability and the functional requirements of the patient [16].
• Many different diagnostic examinations for assessing shoulder instability are used, and a high variety is seen in the use of diagnostic tools [22].
• The consensus statement on shoulder instability aims to improve diagnosis and treatment through universal agreement on outcome measurement tools and tailored treatment based on pathology, patient age, activity demands, and surgeon skills [23].
• Proper identification and treatment of osseous defects resulting in complex shoulder instability is critical in minimizing recurrence [25].
• The Delphi method is a structured communication technique used to allow a panel of experts to achieve a consensus in a systematic manner, resulting in an international consensus statement on shoulder instability covering diagnosis, nonoperative management, surgical options, rehabilitation, and clinical follow-up [26].
• Substantial variability was observed in the scoring of important elements in the radiological report for the evaluation of anterior shoulder instability, regardless of modality [28].
• Over the past several centuries, a number of procedures have been developed to address posterior shoulder instability, particularly as this pathology has become better understood [30].
• The study group achieved strong or unanimous consensus on 63% of statements related to the diagnosis, nonoperative treatment, and labrum repair for posterior shoulder instability [32].
• The FEDS classification, particularly the frequency and etiology of the patient's shoulder instability, may be helpful in identifying patients with a higher likelihood of undergoing surgical treatment [33].
• An expanded assessment framework is useful to estimate the contribution of each component of non-traumatic shoulder instability and offer a framework for targeted rehabilitation [50].
• The validity of testing specific subgroups within the expanded assessment framework for non-traumatic shoulder instability remains to be established [50].
• The approach to the anterior shoulder joint described in the modification of the subscapularis splitting technique is versatile and can be used to treat a variety of types of shoulder instability and accompanying pathologic lesions [55].
• Hyperlaxity is an individual trait and not pathologic, but it may be a factor of risk for having shoulder problems develop [60].
• Multidirectional instability should be distinguished from multidirectional hyperlaxity in the classification of shoulder instability [60].
• The Gerber et al. classification includes chronic locked dislocation, unidirectional instability without hyperlaxity, unidirectional instability with hyperlaxity, multidirectional instability without hyperlaxity, multidirectional instability with multidirectional hyperlaxity, and uni- or multidirectional voluntary instability [60].
• Static instabilities are defined by the absence of classic symptoms of instability yet the humeral head is displaced and fixed superior, anterior, or posterior relative to its normal position on the glenoid fossa [60].
• The diagnosis of static instability is radiological, not clinical [60].
• Static instability may remain asymptomatic for a long period [60].
• Static instabilities can co-exist with dynamic instabilities, such as recurrent anterior instability in a massive cuff tear with superior humeral migration [60].
• Usually the more disabling instability is dynamic and is best treated initially when static and dynamic instabilities co-exist [60].
• Static superior migration of the humeral head is present if the normal distance between the undersurface of the acromion and the most cranial aspect of the humeral head on an anteroposterior radiograph with the shoulder in neutral rotation is decreased [60].
• Seven millimetres is currently the value used to define static superior subluxation [60].
• The cause of cranial migration of the humeral head seems to be insufficiency of the infraspinatus in the presence of a supraspinatus tear [60].
• Isolated supraspinatus, isolated infraspinatus, or combination tears of the supraspinatus and subscapularis tendons do not cause static superior instability [60].
• Loss of the acromio humeral distance to less than 7 mm is associated with loss of strength of abduction and of external rotation [60].
• Static superior subluxation carries a poor prognosis for repair of the rotator cuff tear and some consider it to be a predictor of an irreparable tear [60].
• In the current authors’ experience, superior static subluxation essentially is irreversible by conventional repair techniques [60].
• Static anterior subluxation is a fixed anterior position of the humeral head on the glenoid fossa and often is manifest clinically as moderate to severe shoulder pain [60].
• Static anterior subluxation is partly caused by impingement under the coracoid and coracoacromial arch and loss of anterior elevation [60].
• Static anterior subluxation is usually detected on computed tomography scans or MRI scan taken with the arm in neutral rotation but occasionally may be evident on axillary lateral radiographs [60].
• Static anterior subluxation usually is not associated with recurrent anterior shoulder instability [60].
• To develop a static anterior subluxation without any previous operation, it seems that a combination of a subscapularis tear, a supraspinatus tear, and fatty degeneration of the infraspinatus muscle is necessary [60].
• An isolated tear of the subscapularis tendon and posterosuperior tears usually do not lead to anterior static subluxation [60].
• In the current authors’ experience to date (2002), static anterior subluxation has been irreversible with soft tissue procedure [60].
• Static posterior subluxation is a fixed posterior position of the humeral head on the glenoid fossa on CT or MRI scans with the arm in neutral rotation [60].
• Static posterior subluxation is most frequently but not always associated with congenital dysplasia of the glenoid or with degenerative glenohumeral joint disease [60].
• Static posterior subluxation may be associated with glenoid deformations such as classified by Walch and co-workers [60].
• Static posterior subluxation may be present without any rotator cuff deficiencies [60].
• To date, most authors have found static posterior subluxations to be irreversible [60].
• Inferior subluxation of the shoulder is characterized by straight inferior translation of the humerus relative to the glenoid fossa [60].
• Inferior subluxation may occur from trauma, neurologic injury, septic arthritis, or inadequate restoration of humeral length after arthroplasty [60].
• Inferior subluxation after trauma and surgery, if not associated with permanent nerve injury, usually resolves within 6 weeks but always resolves within 2 years [60].
• Inferior subluxation caused by infection tends to result in joint surface destruction and only successful treatment of infection results in the resolution of the inferior subluxation [60].
• Inferior subluxation caused by neurologic injury or shortening of the humerus also remains symptomatic unless the primary problem can be resolved [60].
• The ABC classification distinguishes three groups of posterior shoulder instability based on the nature of pathology (first-time, dynamic, or static) and two different subtypes based on the pathomechanical causes [65].
• The ABC classification aims to facilitate diagnosis and assist the treatment decisionmaking process for posterior shoulder instability [65].
• The incidence of shoulder arthropathy in patients with shoulder instability is difficult to measure given that the majority of shoulder dislocations occur in younger patients and following such a population until the onset of degenerative arthritis is not feasible [79].
• The high rate of recurrence seen with shoulder dislocation ranges from 10% to 90% after an initial dislocation [79].
• Posterior instability represents about 10% of shoulder instability and has become increasingly recognized and treated in military members [81].
• Classifications of shoulder instability are based on degree, direction, time factors, and mechanism of injury related to the instability [89].
• A chronologic classification for posttraumatic anterior shoulder instability was formulated based on dynamic pathophysiologic reasoning rather than catalog complex descriptions of multiple arthroscopic findings [93].
• The dynamic progression of lesions in posttraumatic anterior shoulder instability suggests a time-dependent, recurrence-dependent worsening of labral and ligamentous pathology in dislocation and subluxation disorders [93].
• The system categorizes instability based on frequency, aetiology, direction, and severity [113].
• Shoulder instability cannot reliably be classified using the ICD-9 coding system [118].
• The ABC classification distinguishes three groups of posterior glenohumeral instability with two different subtypes based on the pathomechanical type of instability and the current standard of treatment [150].
• Shoulder Instability: Alternative Surgical Techniques reviews classification of shoulder instability, pathoanatomy, the concept of glenoid track, and evaluation of bone loss [152].
• Objective and subjective scoring systems correlate significantly with the clinical condition of patients with recurrent shoulder instability and associated bony defects [180].
• Only the WOSI detected differential shoulder function related to shoulder instability [185].
• Patient demographic characteristics in the study were classified according to the Frequency, Etiology, Direction, and Severity classification system for shoulder instability [249].
• There are different patterns of subcritical bipolar bone lesions in anterior shoulder instability that can be divided into 4 groups with a significantly different prevalence [252].
• Subcritical bipolar bone lesion patterns are significant predictors of failure after surgery [252].
• Allocation based on clinical and intraoperative criteria for posteroinferior shoulder instability resulted in 4 groups (A to D) characterized by an increasing traumatic impact [259].
• Categorization into one of four subgroups for posteroinferior shoulder instability might be a valuable tool regarding the choice of the operative treatment options [259].
• The quality of the evidence of studies on Bankart repair for anterior shoulder instability was assessed using the Modified Coleman Methodology Score (MCMS) and the Anterior Shoulder Instability (ASI) Methodology criteria [261].
• The level of evidence of included studies on arthroscopic rotator interval closure for shoulder instability was assessed using the American Academy of Orthopaedic Surgeons classification system for the orthopaedic literature [262].

Clinical Presentation

General Principles and Definitions

• Shoulder instability is a phenomenon with a variety of clinical presentations, and its complex nature has until recently been poorly understood [1].
• Non-traumatic shoulder instability's aetiologies and clinical manifestations are multifactorial [2].
• Instability is defined as a patient experiencing symptoms of some shoulder problem, whereas asymptomatic shoulders with increased joint translation are defined as lax, not unstable [74].
• The diagnosis of shoulder instability can be very easy when the patient presents with an appropriate history of trauma, but is more challenging in patients with a sense of slipping and looseness without a history of macrotrauma [74].
• A thorough clinical exam is the most important factor when determining indication for shoulder instability surgery [27].
• A thorough history and physical examination most often diagnose the degree, direction, frequency, and etiology of shoulder instability [19].
• The history and physical examination are paramount in the diagnosis of a stiff shoulder, and ancillary studies may also be helpful in certain circumstances [7].
• As the knowledge of the basic science behind the pathophysiology of shoulder instability improves and as more clinical reports emerge, the exact indications for arthroscopic stabilization are gradually being refined [13].
• Shoulder anatomy is particularly complex and requires a thorough knowledge by the orthopedic surgeon, and anatomical variants should not be confounded with pathological findings [16].
• Different anatomical lesions can be found depending on the type of instability and the functional requirements of the patient, so the surgical procedures must be carefully chosen to achieve optimal outcomes when treating shoulder instability [16].
• The purpose of this article is to review the current literature concerning shoulder anatomy/pathology related to shoulder stability/instability to improve clinical diagnosis and surgical treatment of our patients [47].
• An expanded assessment framework is useful to estimate the contribution of each component of non-traumatic shoulder instability and offer a framework for targeted rehabilitation, though the validity of testing specific subgroups remains to be established [50].
• Detailed and specific information about prognosis is critical in the management of a first-time anterior shoulder dislocation [45].
• This review evaluates existing data on the presentation of shoulder instability in men and women to determine if there are differences in occurrence, treatment, or functional outcome following management [8].
• In a US epidemiologic population of patients <40 years old, the rate of recurrent anterior shoulder instability was roughly one-third after initial physician consultation [54].
• Recurrent anterior instability of the shoulder is a complex disorder which mainly affects younger population, and generally requires surgical intervention to restore joint stability [123].
• Traumatic shoulder instability in the older patient may result in a wide array of pathologic findings as well as a diversity of clinical presentations [42].
• Children and adolescents with all forms of shoulder instability demonstrate differences in their movement and muscle activity patterns when compared to age- and sex-matched controls [43].
• In this series of anterior shoulder instability in children and adolescents, instability lesions varied significantly by age, with atypical lesions more common in patients <15 years of age and bone loss associated with older age at presentation [126].
• Shoulder instability in female athletes presents commonly as multiple subluxation events [133].
• These findings may represent a pathologic change in the intrinsic characteristics of the shoulder capsule in patients with shoulder instability [132].
• Rotator cuff disease, shoulder instability, and associated lesions are common pathologic conditions of the shoulder involving soft tissues [131].
• The classification of shoulder instability according to Bayley et al. is anchored by three basic or polar groups: I Traumatic structural, II Atraumatic structural, and III Habitual nonstructural (muscle patterning) [80].
• The diagnosis of each type in the Bayley classification is made on the basis of a careful history and clinical examination followed by arthroscopy and, when necessary, functional electro-myography [80].
• Traumatic structural instability is characterized by significant trauma, often a Bankart’s defect, usually unilateral presentation, and no abnormal muscle patterning [80].
• Atraumatic structural instability is characterized by no trauma, structural damage to the articular surfaces, capsular dysfunction, no abnormal muscle patterning, and is not uncommonly bilateral [80].
• Habitual nonstructural (muscle patterning) instability is characterized by no trauma, no structural damage to the articular surfaces, capsular dysfunction, abnormal muscle patterning, and is often bilateral [80].
• There can be much overlap between the polar groups of the Bayley classification, and some patients have a dual pathology [80].
• The authors of the Bayley classification prefer to use the model of a triangle since it better highlights the continuum of presentation which can occur in between the three polar groups [80].
• The system of shoulder dislocation classification developed at the Royal National Orthopaedic Hospital works well for posterior and anterior dislocations and also for subluxations, and complete dislocations [80].
• The history takes account of the degree of trauma required to cause the first dislocation and whether the displacement was complete and requiring formal reduction or incomplete and spontaneously reducing [80].
• The clinical examination looks for signs of ligamentous laxity and specifically for evidence of abnormal muscle pattern recruitment [80].
• The presence or absence of articular surface damage is defined by arthroscopy and functional electromyographic studies look for evidence of abnormal muscle pattern recruitment in patients in whom clinical examination has been negative but suspicion of a nonstructural instability is high [80].
• The concept of instability refers to a patient experiencing symptoms of some shoulder problem, and many asymptomatic shoulders exhibit increased joint translation and are clearly loose during a physical examination [74].
• In the younger and active age groups, the symptom of shoulder instability may be the patient’s presenting complaint [74].
• Although there is often a history of acute traumatic event that resulted in an initial, well-defined onset, in many cases there is no history of such traumatic event [74].
• Since the 1980s, genetic factors in ligamentous laxity have been recognized as significant factors in patients’ perception of shoulder instability [74].
• With the increasing availability of sports trainers at most of the high school, college, and professional competitions, reduction of a dislocation by those personnel results in a history only; there are no ED records or radiographs [74].
• Although the history in these situations is still strong, an examination and radiographs even a few days following the event make this a less-than-challenging diagnosis [74].
• A more challenging problem occurs in patients with a sense of slipping and looseness in their shoulder without a history of macrotrauma [74].
• More often than not, this more subtle instability pattern is associated with a nondescript level of discomfort and diffuse pain around the shoulder girdle [74].
• The discomfort is poorly localized and may be more scapular in location [74].
• The association of such symptoms with paresthesia down the arm is nearly always related to shoulder instability [74].
• There may be a history of repetitive microtrauma with such activities as frequent swimming, gymnastics, or ballet [74].
• Although these activities may not appear to be highly stressful to the joint, they demand muscle function defined by high endurance [74].
• Conventional thought suggests that when the ligament quality and integrity do not contribute to joint stability, the surrounding muscle activity and appropriate proprioceptive activity become more important to maintain a functioning joint [74].
• The sense of instability might occur with the arm only in certain positions or it may be present regardless of arm placement or position [74].
• True symptomatic multidirectional instability is typically symptomatic in midrange positions before the ligament tension reaches the end of its range [74].
• The physician must carefully inquire about which activities and arm positions provoke the symptoms [74].
• Patients with this type of instability might have symptoms that are so incapacitating that they tend to avoid extremes of glenohumeral motion [74].
• Pain is the more common symptom with a shoulder instability based on ligamentous laxity (AMBRI), whereas apprehension is more common with unidirectional traumatic instability (TUBS) [74].
• The classic patient with traumatic instability is a male athlete who sustained an identifiable traumatic event during the course of a violent activity [74].
• Football tackling, a high-speed fall or collision while downhill skiing, or a hyperextension blocking force on an extended arm (such as a basketball blocking shot) are very common scenarios that result in an acute traumatic shoulder dislocation [74].
• The classic patient with multidirectional shoulder instability is the young, asthenic female ballet dancer, swimmer, or volleyball player with nondescript shoulder pain that also involves the scapula and provokes paresthesia down the arm, occurring in the absence of a defined traumatic event [74].
• Isolated symptomatic posterior shoulder instability is most often associated with a very specific event or process [74].
• Although falling on the outstretched arm is a common scenario because the arm is most often placed in the scapular plane to brace the fall and protect the head, and a posterior force is only placed on the hand, such circumstances result much more commonly in anterior dislocation [74].
• Posterior shoulder dislocations are rarely associated with traumatic events that include falls [74].
• Posterior shoulder instability is seen most often in the scenario of electric shocks and epilepsy [74].
• It appears that electrical stimulation to the muscles around the shoulder, when provided in a pathologic setting, can result in posterior instability [74].
• In a clinical setting, the most common cause of weakness is likely a rotator cuff tear, and although some tears are pain free, most patients experience some pain associated with the weak arm [74].
• It is important to ascertain other potential causes of weakness in the complete evaluation of a shoulder-related complaint [74].
• The clinical evaluation is the beginning of the doctor-patient relationship, and the goal is not so much to come up with a diagnosis that will drive to a specific treatment, but rather to carry out an evaluation of the patient that leads to a reasonable management plan [51].
• The four P’s that determine the outcome of treatment are the patient, the shoulder problem experienced, the procedure to treat the patient and the problem, and the physician rendering the treatment [51].
• The author places the patient first on this list because as Osler is quoted as saying, “It is more important to know what patient a disease has than what disease the patient has” [51].
• When introducing myself and shaking the patient’s hand I can sense a lot—healthy or frail, positive or negative, smelling of cigarettes or not [51].
• To learn a bit more, I ask the patient, “Where are you from and what do you do there?” [51].
• In an instant I’ve done a lot to determine if the person might benefit from a surgical approach should one be appropriate for the problem [51].
• Next I like to ask, “What can I help you with today?” giving the patient some uninterrupted time to answer [51].
• A patient with posterior instability may respond with “I can’t do my job,” “I need more pain medicine,” “My lawyer sent me,” or “My shoulder keeps on slipping out when I lift something in front of me”—same diagnosis, but four different problems [51].
• I prefer to avoid dwelling on pain, so rather than asking, “Where does your shoulder hurt?” I ask, “What does your shoulder problem keep you from doing? When does it bother you the most?” [51].
• I follow this with, “How and when did that problem start?”, “How much force was applied to your shoulder in the injury?”, and “Tell me about the treatment you’ve had for it up to now.” [51].
• Trying to learn more about the patient, I ask questions, such as, “How is your overall health?”, “How active are you?”, “What medications are you on?”, and “Have you had prior surgeries and how did they work out?” [51].
• My physical exam starts with a “no touch” approach: “Show me which actions are difficult for your shoulder, and what do you feel is happening when you do these things?” [51].
• To check active motion I ask patients to show me with each shoulder how high they can reach overhead, how far they can externally rotate the shoulder with the arm at the side, how far they can reach across their body, how far they can internally rotate the abducted arm, and how high they can reach up their back [51].
• If patients cannot raise their arm actively, I ask them to show how high they can raise it with the help of the opposite arm [51].
• At this point, without having touched the patient, I usually have a fairly good understanding of the problem and whether the patient is likely to be a good candidate for surgical intervention [51].
• The remainder of my history, physical examination, and plain radiographs seek to refine this understanding [51].
• The authors have done a marvelous job of cataloging the many tests that have been described for evaluating shoulder problems, but they and Dr. Wirth have also pointed out that these tests are rarely capable of discriminating between these problems [51].
• Instead, my exam seeks more tangible findings, such as loss of passive or active ROM, a palpable defect in the rotator cuff, minimal resistance to anterior translation of the humeral head pressed into the glenoid, palpable subacromial crepitus, muscle atrophy, loss of the biceps reflex, or an obvious “clunk” on cross-body adduction [51].
• Bottom line: if the problem is not apparent on history, physical examination, and plain radiographs, or if the patient does not appear to be an excellent surgical candidate, I’m likely to recommend nonoperative management [51].
• This remains the case even if MRIs show “acromioclavicular arthrosis,” “labral fraying,” a “humeral avulsion of the glenohumeral ligament (HAGL)” lesion, or “supraspinatus tendinosis” [51].
• The art of history taking and laying on of hands has been the a priori cornerstone and bulwark of medicine since antiquity [208].
• While the art of diagnosing and directing treatment for the suffering patient dates to the earliest of times, the science of medicine is remarkably recent [208].
• In our present era of unprecedented diagnostic technology, the authors of this chapter have reminded us once again of the importance of a thorough history and careful physical examination, as advocated by Dr. William J. Mayo so many years ago [208].
• Above all things, let me urge upon you the absolute necessity of careful examinations for the purpose of diagnosis [208].
• My own experience has been that the public will forgive you an error in treatment more readily than one in diagnosis, and I fully believe that more than one half of the failures in practice are due to hasty and unmethodic examinations [208].
• The wisdom of these words is clearly evident in the studies that have noted the high incidence of superior labral tears, bone abnormalities, rotator cuff tears, and acromioclavicular joint arthrosis in asymptomatic shoulders [208].
• In a report by Needell and colleagues, dual-echo T2-weighted oblique coronal MRIs were evaluated in 100 asymptomatic patients aged 19 to 88 years, and 75% were diagnosed with acromioclavicular joint arthrosis [208].
• In a similar study acromial joint arthrosis was diagnosed using MRI in 41 (82%) of 50 asymptomatic shoulders [208].
• Moreover, when stratified by age, 93% of those in the over-30 age group exhibited arthritic changes [208].
• In another report Connor and colleagues utilized detailed MRI scans to evaluate the shoulders of asymptomatic elite overhead athletes [208].
• Eight (40%) of 20 shoulders had findings of partial or full-thickness tears of the rotator cuff, but none of the athletes had experienced any subjective symptoms or required any evaluation or treatment for shoulder-related problems during the 5-year study period [208].
• More recently, a study presented at the 2015 annual meeting of the American Academy of Orthopa

Investigations

Clinical Evaluation and Diagnostic Challenges

• Recurrent posterior shoulder instability is an uncommon condition that is often unrecognized, leading to incorrect diagnoses and delays [40].
• Posterior shoulder dislocation is a rare and challenging injury with varied mechanisms of trauma that complicate diagnosis [46].
• Traumatic shoulder instability in patients older than 35 years may result in a wide array of pathologic findings and a diversity of clinical presentations [42].
• A thorough clinical exam is the most important factor when determining the indication for shoulder instability surgery [27].
• The history and physical examination are paramount in the diagnosis of shoulder conditions, with ancillary studies being helpful in certain circumstances [7].
• If the problem is not apparent on history, physical examination, and plain radiographs, nonoperative management is likely recommended even if MRIs show specific pathologies such as labral fraying or HAGL lesions [51].
• Many different diagnostic examinations are used for assessing shoulder instability, with a high variety seen in the use of diagnostic tools [22].

Plain Radiography

• Standardized plain films are almost always sufficient to garner the information needed for shoulder evaluation, and proper radiographic technique is as important as proper surgical technique [41].
• The first key radiographic view is the anteroposterior (AP) view in the plane of the scapula, which shows the superoinferior position of the humeral head relative to the glenoid, osteophytes, joint space narrowing, and medial displacement of the humerus [41].
• The second key radiographic view is the axillary view taken with the arm in the functional position of elevation in the plane of the scapula, referred to as the "truth view" because it demonstrates glenohumeral relationships in functional elevation [41].
• The standardized axillary "truth view" can show posterior subluxation or "functional decentering" that is not evident in images taken with the arm at the side [41].
• The degree of posterior subluxation can be measured by the position of the center of the humeral head in relation to the plane of the scapula, the glenoid face, or the point of contact of the humeral articular surface on the glenoid articular surface [41].
• Focal cortical bone loss at the inferior aspect of the glenoid is a radiographic sign of anterior shoulder instability of traumatic origin [241].
• Radiographic analysis of the Hill-Sachs lesion with a constant, reproducible technique can play a role in the diagnosis of anterior shoulder instability and patient selection for therapeutic intervention [254].
• Radiography can be used for screening patients for significant glenoid bone loss [256].
• The standard shoulder series should include orthogonal views including a true AP view in the scapular plane, an AP view, an axillary view, and a scapular Y view [141].
• The axillary view is necessary for the evaluation of glenohumeral joint instability and may detect occult, locked posterior shoulder dislocation in a patient who exhibits a lack of passive external rotation [141].
• Special radiographic views include the West Point view for anterior glenoid bone loss, the Stryker notch view to evaluate Hill-Sachs lesions after dislocation, and the apical oblique view to evaluate for glenoid rim fracture in instability [141].
• Radiographs seem inferior to CT scans for assessing osseous lesions, especially at the glenoid rim [268].

Computed Tomography (CT)

• CT imaging is frequently used to evaluate fractures of the shoulder, assess for bony lesions in recurrent instability cases, or for preoperative templating for shoulder arthritis [137].
• CT with three-dimensional reconstructions is the advanced imaging study of choice for determining the extent of glenoid bone loss in the setting of shoulder instability [141].
• Glenoid bone loss is a significant factor in recurrent anterior shoulder instability, present in up to 90% of cases, and requires careful diagnosis and quantification to guide treatment selection [52].
• Accurate characterization of glenoid and humeral bone loss is essential for preoperative planning to minimize the risk of recurrent dislocation, with three-dimensional imaging serving as an integral component of this evaluation [274].
• Despite the advantages of MRI in the detection of soft tissue damages in recurrent anterior shoulder instability, CT imaging proved to be more important for glenoid defects [227].
• Advanced imaging modalities are essential for identifying associated lesions, and bony reconstruction procedures should be considered for patients with significant glenoid bone loss or recurrent instability after soft tissue reconstruction [220].
• In the future, CT is expected to be superseded by MRI in anterior shoulder instability [251].
• MDCT arthrography showed better accuracy than MR arthrography in the detection of osseous, cartilage, and labroligamentous injuries related to anterior shoulder instability [276].

Magnetic Resonance Imaging (MRI) and Arthrography

• MRI is the modality of choice for evaluating the rotator cuff, biceps, and subacromial/subdeltoid bursa [137].
• T1-weighted MRI can reveal Hill-Sachs lesions and is often used with magnetic resonance (MR) arthrograms to provide a more detailed picture of the joint surfaces [137].
• T2-weighted MRI provides better visualization of full thickness rotator cuff tears [137].
• MR arthrography is considered the benchmark for evaluation of labral tears and is rarely indicated for evaluation of rotator cuff pathology [137].
• When MRI or MR arthrography is contraindicated, CT arthrography is indicated [137].
• Magnetic resonance arthrography is regarded as the gold-standard imaging modality for shoulder instability [204].
• MR-arthrography is identified as the main tool in diagnosing shoulder instability injuries [234].
• Identification of critical radiographic variables on magnetic resonance arthrography assists in the accurate diagnosis and management of clinically significant posterior shoulder instability [44].
• Static MRI does not appear helpful for diagnosing shoulder instability, however CINE MRI can reproducibly confirm the diagnosis [191].
• The superior-capsular elongation and its diagnostic criteria of measurements by MR arthrography could serve as references for diagnosing atraumatic posteroinferior shoulder instability [258].
• ZTE MRI demonstrated high reproducibility for the evaluation of glenoid bone defect in shoulders with anterior instability [264].
• MRI is a valid imaging tool to diagnose and measure osseous lesions of the shoulder in adolescents [265].
• The swelling and diminished findings of the anteroinferior capsulolabral complex on conventional MRI were moderately related to pathologic arthroscopic findings in patients with traumatic anterior shoulder instability [271].
• MR images did not show the detachment in three shoulders, while arthroscopy proved the detachment in these shoulders [273].
• A thorough clinical exam is the most important factor when determining indication for shoulder instability surgery, even when radiologist reported magnetic resonance arthrogram studies are normal or pathological [27].
• Arthrotomography of the glenoid labrum is a helpful adjunct in substantiating the diagnosis of shoulder instability and in planning the choice of surgical reconstruction [266].
• The study investigated whether unstable painful shoulder and anterior instability are associated with differences in scapula morphology using magnetic resonance imaging [267].

Ultrasonography

• Ultrasonography is a low-cost alternative to MRI and arthrography for evaluating both skeletal and soft-tissue structures of the shoulder [137].
• Ultrasonography can provide immediate, real-time visualization of the rotator cuff, biceps tendon, and calcific deposits [137].
• Ultrasonography can be used to measure the subacromial space and detect atrophy of rotator cuff muscles [137].
• As a result of providing images in real-time, ultrasonography can evaluate impingement in various positions and motions [137].
• Ultrasonography is highly operator dependent and is not as useful for evaluating labral tears or rotator cuff tears that are very small or larger than 3 cm [137].

Research and Standardization

• The Multicenter Orthopaedic Outcomes Network (MOON) Shoulder Group was formed to conduct large multicenter studies on conditions of the shoulder and has expanded its scope to include other shoulder pathology [5].
• MOON Shoulder Instability is an offshoot of MOON Shoulder, focusing on patients undergoing surgical treatment for shoulder instability [5].
• Future studies should attempt to control for all relevant factors, use advanced imaging for glenoid bone loss measurements, and consider a lower predictive threshold for the Instability Severity Index Score [270].

Treatment

Nonoperative Management

• Nonoperative management of anterior shoulder instability is associated with high rates of poor outcomes at 17-year follow-up [4].
• At long-term follow-up, nearly 40% of patients treated non-operatively for posterior shoulder instability eventually require surgery [9].
• A history of multiple instability episodes prior to presentation was the greatest predictor of recurrent instability and failure of nonoperative treatment and progression to surgery [38].
• Primary non-operative management is a prominent risk factor for recurrence of shoulder instability [115].
• The recurrence of anterior shoulder instability can be as high as 86.7% in high-risk patients who are treated nonoperatively after their first incident of instability [88].
• Patients treated conservatively for anterior shoulder instability were far more likely to achieve a successful outcome defined as completing a subsequent season in their same sport compared to surgical patients [92].
• Nonoperative treatment of shoulder instability has substantial societal costs [172].
• For multidirectional instability, all patients should undergo extensive physical therapy for 6 to 9 months prior to consideration of surgical treatment [17].
• Physical therapy for multidirectional instability should focus on rotator cuff strengthening, scapular kinematics, and proprioceptive training [17].
• Approximately 20% of patients with multidirectional instability fail nonsurgical management [17].
• Surgery for multidirectional instability is contraindicated for voluntary dislocators and patients who have not attempted physical therapy [17].
• Nonsurgical treatment should always be attempted first for posterior shoulder instability after a single traumatic injury [34].
• After a single traumatic posterior injury, the arm should be immobilized in neutral rotation with the elbow in adduction for 1 to 2 weeks followed by therapy [34].
• Nonsurgical treatment including physical therapy, activity modification, and anti-inflammatory agents should be considered for patients with minimal symptoms of posterior instability [73].
• Surgical intervention is contraindicated for voluntary posterior dislocators due to an extremely high failure rate [73].
• NHL team physicians strongly favor nonoperative management in-season for initial posterior instability events of the shoulder [193].
• A comprehensive conservative management program includes appropriate immobilization for a minimum of three weeks followed by intensive strengthening to restore the balance and stability of the shoulder musculature [236].
• Operative interventions should be approached with caution in patients with atraumatic shoulder instability, and physiotherapy should always be the primary management strategy [225].
• Eighty per cent of patients with atraumatic shoulder instability should respond to non-operative measures [225].
• Conservative treatment for recurrence in failed instability shoulders could be considered for patients with low functional demands and no associated shoulder injuries [235].

Operative Management: Anterior Instability

• Arthroscopic anterior capsulolabral repair accounts for more than 90% of surgical cases for anterior shoulder instability in North America [37].
• An isolated arthroscopic soft-tissue stabilization is best suited for patients with little to no glenoid bone loss, minimal humeral bone loss, and good capsular and labral tissue quality [37].
• A large 2017 cohort study showed subjective instability in 62% and revision surgery in 32% of patients undergoing arthroscopic Bankart repair after multiple episodes of instability [37].
• The open Bankart procedure typically involves a pants-over-vest capsular shift in addition to labral repair [37].
• A meta-analysis of 22 studies found no difference in rates of recurrent instability or patient-reported outcomes between open and arthroscopic anterior stabilization techniques [37].
• If the definition of recurrent instability is extended to include apprehension and subluxations, open repairs outperform arthroscopic repairs [37].
• Failure rates in all available studies are lower with open repairs than arthroscopic repairs in contact athletes [37].
• A humeral avulsion of the glenohumeral ligaments typically warrants an open repair with anchors back to the humeral neck [37].
• Early arthroscopic stabilization by anterior capsule-labrum reinsertion after initial anterior shoulder dislocation is associated with a low 10-year recurrence rate of 35% compared to non-operative management [221].
• First-time dislocators who underwent surgical stabilization had better outcomes than recurrent dislocators with regard to requiring additional surgery for recurrent dislocation, with rates of 7% versus 32% [140].
• In a randomized clinical trial comparing open versus arthroscopic Bankart repair, an increased rate of recurrence was noted after arthroscopic repair at 23% versus 11% in open repair [140].
• The highest rate of recurrence in the comparison of open versus arthroscopic Bankart repair was noted in males younger than 25 years with Hill-Sachs lesions [140].
• A systematic review of more recent meta-analyses demonstrated no difference in recurrence between open and arthroscopic anterior stabilization techniques [140].
• The indications for an isolated soft-tissue procedure in anterior shoulder instability are now narrower, with the ideal candidate presenting with minimal glenoid bone loss of 13.5% [61].
• Successful results were obtained in patients younger than 40 years with both primary and recurrent anterior shoulder instability after arthroscopic treatment [149].
• Arthroscopic surgery is an acceptable treatment if recurrent instability occurs consistently at ≤23.8% [165].
• The success of treating anterior glenohumeral instability relies on multiple factors, including glenoid bone loss [138].
• Surgical soft-tissue stabilization might be more aggressively indicated in cases of primary shoulder dislocation, whereas recurrent instability with bone loss should be referred to experienced high-volume specialists [82].
• Current evidence supports the safety and efficacy of both the Latarjet and free bone block procedures for anterior shoulder stabilization in the presence of glenoid bone loss [164].
• The critical size of a glenoid defect is reported to be 25% to 26% of the glenoid width [169].
• The acceptable size of a glenoid defect is less than 17% and the unacceptable defect size is more than 25% [169].
• For an on-track Hill-Sachs lesion, soft tissue repair alone, such as arthroscopic Bankart repair, is sufficient [169].
• For an off-track Hill-Sachs lesion with a small glenoid defect, remplissage may be indicated [169].
• For an off-track Hill-Sachs lesion with a large glenoid defect, the Latarjet procedure may be preferable [169].
• If a glenoid defect is larger than the critical size, it must be fixed by iliac bone graft or coracoid transfer [169].
• In a series of 100 patients with recurrent anterior dislocation, 93% had an on-track Hill-Sachs lesion and were treated by arthroscopic Bankart repair [169].
• In a series of 100 patients with recurrent anterior dislocation, 7% had an off-track Hill-Sachs lesion and were treated by the Latarjet procedure [169].
• The main indications for long head of biceps tendon transfer are shoulder instability in high-impact athletes with capsule-labrum reconstruction and poor tissue quality of the labrum in patients with multiple long-term dislocations [214].
• Stabilization of the dominant shoulder resulted in residual surgery-related functional impairments on both sides, whereas stabilization of the nondominant shoulder resulted in impairments primarily noted in the nondominant, operative shoulder [90].
• Patients in the no-sling group after open Latarjet procedures did not undergo sling immobilization postoperatively and were instructed to avoid active elevation and abduction [233].
• Patients in the sling group after open Latarjet procedures were instructed to wear a sling in internal rotation with the arm at the side of the body for the first 3 weeks postoperatively [233].

Operative Management: Posterior Instability

• Primary arthroscopic treatment of posterior shoulder instability is associated with favorable outcomes and high return to sport and work rates [148].
• Arthroscopic stabilization of posterior shoulder instability resulted in good outcomes with high patient satisfaction and low rates of recurrent instability, revisions, and residual pain [163].
• Arthroscopic treatment of posterior shoulder instability is an effective means to improve symptoms associated with recurrent posterior subluxation of the shoulder [158].
• Treatment of posterior shoulder instability by capsulolabral reconstruction leads to good clinical outcomes; however the recurrence rate is high [53].
• The benchmark treatment for unsuccessful nonsurgical treatment of posterior instability is an anchor-based arthroscopic capsulolabral repair [73].
• Recurrent instability rates for posterior stabilization are low at 8%, and 90% of patients return to sport [73].
• In throwers, only 58% were able to return to sport at the same level after posterior stabilization [73].
• Revision surgery is only required in 6% of patients with posterior instability, and the outcomes are far inferior to those of index surgery, with only 15% returning to sport at their preoperative level [73].
• Beyond 20% posterior bone loss, an isolated labral repair cannot restore adequate shoulder stability [73].
• Chronic attritional bony injuries in posterior instability require grafting using the iliac crest, distal tibia, or scapular spine [73].
• The iliac posterior shoulder bone-block is effective in managing instances of involuntary posterior shoulder instability, showing satisfactory results in terms of non-recurrence, pain relief, and function recovery [228].
• Recurrence is the most common complication of posterior instability surgery and is reported to be 8.5% in the general population [34].
• Recurrence rates for posterior instability surgery are highest in overhead athletes and increase with posterior glenoid bone loss >20%, which should be considered a contraindication to arthroscopic soft-tissue stabilization alone [34].
• Overtightening of the posterior capsule can lead to anterior subluxation or coracoid impingement [34].
• In arthroscopic labral repair for posterior instability, a high lateral portal provides better access than a standard posterior portal [34].
• Postoperatively for posterior instability, the shoulder should be placed in a rigid immobilizer with the arm abducted to 30° in neutral rotation [34].
• Strengthening for posterior instability should begin at 12 weeks postoperatively [34].
• Patients may return to heavy labor or contact sports 6 months after posterior instability surgery [34].
• The pooled published rate of return to any sport after posterior instability surgery is 91%, and to preinjury level of sport is 67% [34].
• Surgical shoulder stabilization in an athlete after a first episode of posterior instability is not indicated in all patients [206].
• The thresholds defined for interpreting patient outcomes following arthroscopic stabilization for posterior shoulder instability allow for earlier detection of recurrent posterior instability [58].

Operative Management: Multidirectional Instability

• Arthroscopic pancapsular plication with or without rotator interval closure is a surgical technique for multidirectional instability [17].
• If labral pathology is encountered during multidirectional instability surgery, anterior or posterior labral repair is indicated [17].
• Capsulorrhaphy for multidirectional instability should address the inferior redundancy in a balanced fashion to avoid asymmetric tightening [17].
• Open anterior-inferior capsular shift is a surgical technique for multidirectional instability [17].
• Recurrence of multidirectional instability is 7% for both open and arthroscopic techniques [17].
• Complications of multidirectional instability surgery include axillary nerve injury, stiffness (rare), and subscapularis insufficiency after open procedure [17].
• Adolescent multidirectional shoulder instability refractory to non-surgical management appears to have long-term outcomes after surgical intervention that are comparable to adolescent patients with unidirectional instability [155].

General Surgical Considerations and Outcomes

• No treatment has proved to be definitive for shoulder stiffness, and the treatment approach should be tailored to each individual patient [7].
• The Western Ontario Shoulder Instability Index (WOSI) is recommended for following up patients with shoulder instability [36].
• To assess the effectiveness of an arthroscopic stabilization procedure for anterior shoulder instability using the Rowe score, a difference of at least 9.7 in the score is clinically relevant [121].
• Despite the absence of evidence-based guidelines, there exists minimal variability in recommendations between North American and European shoulder surgeons regarding return to play criteria [239].
• RCTs reporting on shoulder instability surgery are well performed but poorly reported [64].
• The Delphi method was used to achieve an international consensus statement on shoulder instability covering diagnosis, nonoperative management, surgical options, rehabilitation, and clinical follow-up [26].
• Successful treatment of anterior instability of the shoulder requires a balance between restoring joint stability and minimizing loss of glenohumeral motion [153].
• There were no significant racial disparities seen between white and minority patients in regard to the rates of non-operative follow up for anterior shoulder instability [231].

Complications

Recurrence and Failure of Stabilization

• Recurrent shoulder instability is the most common complication after labral repair [201].
• Most reported rates of recurrent instability after arthroscopic Bankart repair are less than 10% [201].
• With a follow-up of 97%, about one third of the stabilized shoulders experienced at least one redislocation after 8 to 10 years [62].
• Patients undergoing arthroscopic capsulolabral revision repair (ACRR) for recurrent anterior shoulder instability had a recurrent instability rate of 27.6% at a minimum 20-year follow-up [83].
• About 1 in 3 patients suffered from shoulder instability, of whom approximately half reported a redislocation postoperatively, following arthroscopic Bankart repair with a minimum 20-year follow-up [237].
• While recurrence rates increased over time, no revision surgeries were required in a 10-year follow-up study of arthroscopic Bankart repair [209].
• The instability severity index score permits precise identification of patients at risk for failure of primary shoulder stabilization [12].
• Multiple instability events at initial presentation are the major predictor of failure of nonoperative treatment for anterior shoulder instability [6].
• In a prospective study of 200 shoulders in 183 athletes who underwent arthroscopic posterior capsulolabral repair, results were durable at 3 years with 90% of athletes returning to sport [35].
• In the adolescent population, 92% of patients who underwent posterior capsulolabral repair were stable at 5 years follow-up [35].
• Instability-related complications occurred only in the capsulabral group, and the incidence increased with time in patients returning to professional Australian Rules Football after surgery for traumatic anterior shoulder instability [205].

Nerve Injury

• Axillary nerve injury is a reported complication of multidirectional instability (MDI) surgical treatment [18].
• Nerve injuries can be permanent following interscalene blocks used for shoulder instability surgery [29].
• A complete neurologic examination should be done early in the postoperative period to document any nerve deficits [223].
• If no recovery of a nerve deficit is noted after 6 weeks, an electromyographic examination should be obtained and repeated at 3 months [223].
• If no recovery has occurred as evident by electromyography at 3 months, exploration of the nerve should be considered [223].
• Most nerve injuries are neurapraxias that recover with time [223].

Stiffness and Range of Motion

• Stiffness is a rare complication of multidirectional instability (MDI) surgical treatment [18].
• Additional capsular tightening or shifting in shoulders with traumatic anterior instability can result in a stiff shoulder [29].
• Capsular plication in shoulders with AMBRI type of instability may result in a stiff, redundant shoulder if overtightened [29].

Hardware and Implant Complications

• Suture anchors misplaced during arthroscopic instability repairs can give rise to secondary degenerative joint disease or "anchor arthropathy" [29].
• The Latarjet procedure for anterior shoulder instability results in an overall complication rate of 16.1% and a reoperation rate of 2.6% [173].
• Serious complications at short-term follow-up for the Latarjet procedure appear rare [173].
• Screw-related problems are a risk associated with the routine use of bone transfers such as the Latarjet procedure [29].
• Damage to the subscapularis is a risk associated with the routine use of bone transfers such as the Latarjet procedure [29].
• Difficulty in revision is a risk associated with the routine use of bone transfers such as the Latarjet procedure [29].
• Increased risk of arthritis is a risk associated with the routine use of bone transfers such as the Latarjet procedure [29].
• Subscapularis insufficiency is a complication after open procedures for multidirectional instability (MDI) [18].
• Recurrence of MDI is 7% for both open and arthroscopic techniques [18].

Arthritis and Joint Degeneration

• The natural history of the first time shoulder dislocations is bound up with arthropathy [69].
• There is no doubt that the humeral head suffers cartilage damage with shoulder dislocation [79].
• Osteochondral lesions of the humeral head were noted in 34 of 63 patients with first-time traumatic dislocations evaluated arthroscopically within 10 days [79].
• Chondral lesions were noted in an additional 23 of 63 patients with first-time traumatic dislocations evaluated arthroscopically within 10 days [79].
• Osteochondral lesions were found in six of 24 shoulders with first-time anterior shoulder dislocation assessed arthroscopically 1 to 3 days after injury [79].
• All remaining 18 of 24 shoulders with first-time anterior shoulder dislocation assessed arthroscopically 1 to 3 days after injury were noted to have chondral lesions [79].
• Of 88 patients with acute instability (within 90 days of index injury to surgery), 24% had grade I or higher chondral lesions [79].
• Of 88 patients with acute instability (within 90 days of index injury to surgery), 12% had Grade III or IV chondral damage [79].
• Use of intra-articular infusion of local antibiotics via a pain pump after arthroscopic instability repairs results in a risk of glenohumeral chondrolysis [29].
• Adolescent athletes who present with a history of anterior shoulder instability have a high incidence of bipolar bone loss [229].
• Anteroinferior glenoid rim fractures are a relatively common finding in shoulder instability patients aged 50 years or older [238].
• 41 of 177 patients (23.2%) with first-time anterior shoulder instability occurring at age ≥50 years had radiographic evidence of an anteroinferior glenoid rim fracture at initial presentation [238].

Arthroplasty-Related Instability

• Instability is the second leading cause of complications associated with shoulder arthroplasty, with a reported prevalence of 4% and accounting for 30% of all complications [240].
• In a meta-analysis of 11 series of total shoulder arthroplasties that included 838 patients, the incidence of postoperative dislocation was 1.2% over a follow-up period of 20 to 54 months [240].
• Approximately 80% of instability complications after total shoulder arthroplasty involve anterior or superior instability [240].
• Most instability complications after total shoulder arthroplasty are the result of soft-tissue deficiency [240].
• Anterior instability after total shoulder arthroplasty is most commonly associated with subscapularis failure, glenoid component malposition, or anterior deltoid dysfunction [240].
• Anterior instability secondary to subscapularis rupture is generally a consequence of operative technique, tissue quality, inappropriate physical therapy, or the use of oversized components [240].
• Anterior instability can be caused by the use of a humeral head that is too small for the joint volume [240].
• A torn subscapularis tendon is likely to be underreported and will not correlate with the postoperative physical examination [240].
• A torn subscapularis tendon can contribute to anterior instability and must be repaired to regain joint stability [240].
• Often the subscapularis is irreparable, necessitating a revision to reverse arthroplasty [240].
• Posterior instability after total shoulder arthroplasty has been attributed most often to malposition of the components [240].
• Posterior glenoid erosion with excessive component retroversion and soft-tissue imbalance has been implicated in the development of posterior instability after total shoulder arthroplasty [240].
• If the glenoid or humeral component is placed in too much retroversion, posterior instability may occur and revision is recommended [240].
• If the capsule is stretched from long-standing posterior wear on the glenoid, it may require imbrication to gain stability [240].
• Patients with posterior glenohumeral subluxation associated with long-standing osteoarthritis or a history of chronic posterior instability are at increased risk for posterior instability after shoulder arthroplasty [240].
• Inferior instability is related to the loss of normal humeral height and is most common after hemiarthroplasty for proximal humeral fractures [240].
• Removal of too much of the proximal humerus, with resultant inferior placement of the humeral head, can lead to inferior instability [240].
• Patients with inferior instability usually have difficulty elevating the arm past the horizontal plane because of weakness of the deltoid caused by shortening of the humerus [240].
• Revision surgery is usually necessary to restore humeral length and regain deltoid strength in cases of inferior instability [240].
• The overall complication rate after total shoulder arthroplasty is estimated to be approximately 15% [244].
• The most commonly reported complications after total shoulder arthroplasty, in order of frequency, are component (primarily glenoid) loosening, glenohumeral instability, rotator cuff tear, periprosthetic fracture, infection, implant failure including dissociation of modular prostheses, and deltoid weakness or dysfunction [244].
• Complications after total shoulder arthroplasty tend to occur late in the postoperative course (5 to 10 years after surgery) [244].
• Component loosening has been reported to occur approximately 8 years after total shoulder arthroplasty surgery [244].
• Infection has been reported to occur at 12 years after total shoulder arthroplasty surgery [244].
• Periprosthetic fractures have been reported to occur at 6 years after total shoulder arthroplasty surgery [244].
• Reverse total shoulder arthroplasty initially resulted in relatively high complication rates (50%) [244].
• With improved techniques and better understanding of the device, the complication rate for reverse total shoulder arthroplasty has fallen to 6% recently reported [244].
• The most common complications after reverse total shoulder arthroplasty are scapular notching, hematoma formation, glenoid dissociation such as baseplate failure or aseptic loosening, glenohumeral dislocation, acromial and scapular spine fractures, infection, loosening or dissociation of the humeral component, and nerve injury [244].
• In a study of 33 series (2540 shoulders) of unconstrained total shoulder arthroplasties, instability occurred in 4.9% of all shoulders [223].
• In a study of 33 series (2540 shoulders) of unconstrained total shoulder arthroplasties, instability accounted for 30% of all complications [223].
• In a study of 33 series (2540 shoulders) of unconstrained total shoulder arthroplasties, superior instability occurred in 3% of all shoulders [223].
• In a study of 33 series (2540 shoulders) of unconstrained total shoulder arthroplasties, posterior instability occurred in 1% of all shoulders [223].
• In a study of 33 series (2540 shoulders) of unconstrained total shoulder arthroplasties, anterior instability occurred in 0.9% of all shoulders [223].

Other Complications

• Complications associated with arthroscopic shoulder stabilization are relatively common [248].
• Excluding recurrence, complications associated with arthroscopic shoulder stabilization are rarely disabling [248].
• Current statistics undoubtedly underestimate the true incidence of complications associated with arthroscopic shoulder stabilization [248].
• Many complications, including neurovascular injuries and articular damage, are preventable and can be minimized through familiarity with anatomy, proper surgical technique and instrumentation, and clinical experience [248].
• Despite careful patient selection and attention to labral pathology and capsular laxity, arthroscopic repairs continue to have success rates lower than those achieved through open means [248].
• The outcomes at 3 years' follow-up for revision of failed Latarjet with the Eden-Hybinette surgical technique were satisfactory in 80% of patients [72].
• 86% of patients had stable shoulders at 3 years' follow-up after revision of failed Latarjet with the Eden-Hybinette surgical technique [72].
• This long-term follow-up study demonstrated that the open Latarjet procedure is a safe and reliable technique for recurrent anterior shoulder instability [75].
• Short-term outcomes for pre-shaped allograft for glenoid reconstruction in anterior shoulder instability are reassuring [63].
• More research is needed to study long-term graft union, graft resorption, glenohumeral arthritis, and patient outcomes including recurrent shoulder instability for pre-shaped allograft for glenoid reconstruction [63].
• At mid-term follow-up, patients with a history of anterior shoulder instability undergoing total shoulder arthroplasty can expect continued improvement in function compared with preoperative values [68].

Recovery

Non-Operative Management

• The cornerstone of treatment for instability remains immobilization followed by rehabilitation, but the optimal nonoperative treatment of a shoulder dislocation is still unknown and deserves further study [19].
• Recent studies continue to demonstrate a role for nonoperative treatment in the successful long-term management of anterior glenohumeral instability [78].

Operative Management

• Early arthroscopic stabilization can decrease recurrence rates and improve functional outcomes in young (>25 years old), high-risk patients with first-time anterior dislocations and an associated Bankart lesion [19].
• In the absence of severe capsular laxity or bony deficiency, arthroscopic stabilization is considered a first-line therapy in recurrent anterior and posterior instability of traumatic origin [19].
• Recent evidence suggests that participation in a contact sport is not a contraindication to arthroscopic stabilization [19].
• Athletes may return to play after a shoulder dislocation or after stabilization surgery when strength and mobility have normalized [19].
• Modern suture-anchor techniques and shoulder-specific instrumentation have yielded results comparable to those of open surgery; however, many believe that open surgery has a slightly lower recurrence rate at the cost of some loss of external rotation [19].
• Open surgery should be strongly considered in cases of severe capsular laxity or deficiency, glenoid or humeral bone loss, avulsion of the capsule from the humeral side, documented connective tissue disorders, and for revision stabilizations [19].
• MDI often manifests as bilateral shoulder subluxations in a susceptible patient and should be treated with an extended course of physical therapy [19].
• Arthroscopic and open capsular shifts have been successful in restoring stability and decreasing pain, but thermal capsulorrhaphy has recently shown a high complication rate [19].
• Generally, the results of arthroscopic treatment are less predictable in patients with greater than 2+ instability in two or more directions, patients with 3+ (locking) unidirectional patterns without evidence of capsular injury, and those with atraumatic posterior instability [19].
• In patients with greater than 2+ instability in two or more directions, patients with 3+ (locking) unidirectional patterns without evidence of capsular injury, and those with atraumatic posterior instability, an open capsular shift may provide a more predictable outcome [19].
• Short-term outcomes of pre-shaped allograft for glenoid reconstruction in anterior shoulder instability are reassuring, but more research is needed to study long-term graft union, graft resorption, glenohumeral arthritis, and patient outcomes including recurrent shoulder instability [63].
• The outcomes at 3 years' follow-up for revision of failed Latarjet with the Eden-Hybinette surgical technique were satisfactory in 80% of patients and 86% had stable shoulders [72].
• Patients undergoing ACRR for recurrent anterior shoulder instability had a recurrent instability rate of 27.6% at a minimum 20-year follow-up [83].
• This combination of arthroscopic remplissage in addition to the classic Bankart repair has long-term outcomes in terms of the recurrence rate and does not significantly influence the range of motion of the shoulder [188].
• Arthroscopic Bankart repair for anterior shoulder instability has been shown to result in excellent long-term functional outcomes despite a relatively high rate of recurrent instability necessitating revision surgery [215].
• The number of episodes of dislocation before surgery and the delayed surgical intervention did not increase the recurrent anterior shoulder instability rates postoperatively [275].
• In a cohort of young patients undergoing arthroscopic surgery for posterior shoulder instability, there was no significant difference in reoperation rate and recurrence of symptoms between athletes who underwent objective return to sport testing and those who were released to sport on a time-based protocol [277, 278].
• None of the patients has had instability after an average follow-up of 26 months following repair of humeral and glenoid detachment of the anterior inferior glenohumeral ligament [279].
• The prospective study of an initial series of 29 shoulders with a minimum of 26 months’ follow-up (mean, 36 months) shows 1 poor result because of the recurrence of instability (arthroscopic revision has had a successful outcome), 1 fair result, 2 good, and 25 excellent results (according to the Duplay scale) [281].
• Publication period subgroup analysis suggests that historical instability differences were driven primarily by earlier studies, whereas contemporary studies show comparable instability and functional outcomes between arthroscopic and open approaches [282].

Prognosis and Risk Factors

• Characteristics related to a history of instability (age <20 years at first instability episode, larger number of dislocations, ≥2 years between first dislocation and surgery) were found to be risk factors for the development of an off-track HS lesion [280].

Key Evidence

• [L5] Shoulder instability is a phenomenon with a variety of clinical presentations, and its complex nature has until recently been poorly understood. [1] (10.1016/j.cuor.2004.04.002)
• [L5] Non-traumatic shoulder instability's aetiologies and clinical manifestations are multifactorial. [2] (10.1177/17585732251320070)
• [L4] The MOON Shoulder Instability Study has enrolled the largest cohort of patients undergoing shoulder stabilization to date. [3] (10.1177/0363546518755752)
• [L4] At long-term follow-up of 17 years, a high rate of poor outcomes was observed following nonoperative management of anterior shoulder instability. [4] (10.1016/j.jse.2021.07.016)
• [L3] Most patients younger than 40 years with shoulder instability who were initially treated nonoperatively for 6 months were definitively treated without surgery. [6] (10.1016/j.arthro.2021.03.047)
• [L4] This review evaluates existing data on the presentation of shoulder instability in men and women to determine if there are differences in occurrence, treatment, or functional outcome following management. [8] (10.2106/jbjs.rvw.19.00007)
• [L3] Long-term follow-up demonstrates that nearly 40% of patients treated non-operatively for posterior shoulder instability eventually require surgery. [9] (10.1177/2325967118s00098)
• [L4] Biomechanical studies on posterior shoulder instability remain limited in the literature, with current models performed in a static manner which limits their translation for explaining a dynamic pathology. [10] (10.5312/wjo.v9.i11.245)
• [L5] Proper evaluation of bone loss best determines shoulder instability surgical indications and outcomes. [11] (10.1016/j.arthro.2021.01.004)
• [L5] Failure of primary shoulder stabilization procedures is often related to uncorrected anatomic pathology, and the instability severity index score permits precise identification of patients at risk. [12] (10.1016/j.arthro.2010.11.057)
• [Paper] As the knowledge of the basic science behind the pathophysiology of shoulder instability improves and as more clinical reports emerge, the exact indications for arthroscopic stabilization are gradually being refined. [13] (10.1016/s0278-5919(05)70294-5)
• [L3] The 1-year outcomes in this prospective study suggest superiority of operative over non-operative treatment for posterior shoulder instability. [14] (10.1016/j.otsr.2017.08.004)
• [L5] [15] (10.1177/03635465000280062501)
• [L1] Surgical treatment of primary, traumatic, anterior shoulder instability results in reduced rates of recurrence compared with nonsurgical treatment at 10-year follow-up. [17] (10.1016/j.arthro.2006.11.026)
• [L1] The early and midterm results of arthroscopic stabilization of the shoulder for posterior instability are promising. [20] (10.1016/j.arthro.2014.11.009)
• [L4] The short-term outcome in this small series of arthroscopic revision surgery in shoulder instability is challenging and encouraging. [21] (10.1016/s1058-2746(96)80315-6)
• [L4] Many different diagnostic examinations for assessing shoulder instability are used and a high variety is seen in the use of diagnostic tools. [22] (10.1007/s00402-016-2443-7)
• [L5] The consensus statement aims to improve diagnosis and treatment of shoulder instability through universal agreement on outcome measurement tools and tailored treatment based on pathology, patient age, activity demands, and surgeon skills. [23] (10.1016/j.arthro.2009.06.022)
• [L4] They are considered safe and clinically effective for the management of anterior shoulder instability with glenoid bone loss. [24] (10.5435/jaaos-d-22-00837)
• [Paper] Proper identification and treatment of osseous defects resulting in complex shoulder instability is critical in minimizing recurrence. [25] (10.1016/j.csm.2013.07.002)
• [L5] The Delphi method is a structured communication technique used to allow a panel of experts to achieve a consensus in a systematic manner, resulting in an international consensus statement on shoulder instability covering diagnosis, nonoperative management, surgical options, rehabilitation, and clinical follow-up. [26] (10.1016/j.arthro.2021.11.052)
• [L3] A thorough clinical exam is the most important factor when determining indication for shoulder instability surgery. [27] (10.1016/j.xrrt.2026.100675)
• [L5] Substantial variability was observed in the scoring of important elements in the radiological report for the evaluation of anterior shoulder instability, regardless of modality. [28] (10.1016/j.jseint.2024.03.012)
• [L5] Over the past several centuries, a number of procedures have been developed to address posterior shoulder instability, particularly as this pathology has become better understood. [30] (10.1016/j.jses.2019.08.008)
• [L5] The study group achieved strong or unanimous consensus on 63% of statements related to the diagnosis, nonoperative treatment, and labrum repair for posterior shoulder instability. [32] (10.1016/j.arthro.2024.04.035)
• [L2] The FEDS classification, particularly the frequency and etiology of the patient's shoulder instability, may be helpful in identifying patients with a higher likelihood of undergoing surgical treatment. [33] (10.1177/2325967115607434)
• [L2] We recommend using it in following up patients with shoulder instability. [36] (10.1016/j.otsr.2016.10.024)
• [L3] A history of multiple instability episodes prior to presentation was the greatest predictor of recurrent instability and failure of nonoperative treatment and progression to surgery. [38] (10.1016/j.asmr.2023.03.014)
• [L5] Recurrent posterior shoulder instability is an uncommon condition often unrecognized, leading to incorrect diagnoses and delays. [40] (10.5435/00124635-200608000-00004)
• [L4] Traumatic shoulder instability in the older patient may result in a wide array of pathologic findings as well as a diversity of clinical presentations. [42] (10.1177/2325967115584318)
• [L3] [43] (10.1016/j.jse.2024.01.043)
• [L3] Identification of these critical radiographic variables on magnetic resonance arthrography assists in the accurate diagnosis and management of clinically significant posterior shoulder instability. [44] (10.1177/0363546516660076)
• [L2] Detailed and specific information about prognosis is critical in the management of a first-time anterior shoulder dislocation. [45] (10.1016/j.jse.2010.10.037)
• [L4] Posterior shoulder dislocation is a rare and challenging injury with varied mechanisms of trauma that complicate diagnosis. [46] (10.5435/jaaos-22-03-145)
• [L5] The purpose of this article is to review the current literature concerning shoulder anatomy/pathology related to shoulder stability/instability to improve clinical diagnosis and surgical treatment of our patients. [47] (10.1016/j.arthro.2011.05.017)
• [L5] An expanded assessment framework is useful to estimate the contribution of each component of non-traumatic shoulder instability and offer a framework for targeted rehabilitation, though the validity of testing specific subgroups remains to be established. [50] (10.1177/1758573214548934)
• [L5] Glenoid bone loss is a significant factor in recurrent anterior shoulder instability, present in up to 90% of cases, and requires careful diagnosis and quantification to guide treatment selection ranging from soft-tissue repair to bony reconstitution. [52] (10.5435/00124635-200908000-00002)
• [Paper] Treatment of posterior shoulder instability by capsulolabral reconstruction leads to good clinical outcomes; however the recurrence rate is high. [53] (10.1016/j.otsr.2017.08.002)
• [L3] In a US epidemiologic population of patients <40 years old, the rate of recurrent anterior shoulder instability was roughly one-third after initial physician consultation. [54] (10.1177/0363546519886861)
• [L4] This approach to the anterior shoulder joint is versatile and can be used to treat a variety of types of shoulder instability and accompanying pathologic lesions. [55] (10.1097/00132589-200303000-00003)
• [L4] The thresholds defined in this study can provide a guideline for interpreting patient outcomes following arthroscopic stabilization for posterior shoulder instability, allowing for earlier detection of recurrent posterior instability. [58] (10.1016/j.jseint.2025.08.006)
• [Paper] The indications for an isolated soft-tissue procedure in anterior shoulder instability are now narrower; the ideal candidate presents with minimal glenoid bone loss (13.5%). [61] (10.2106/jbjs.rvw.26.00033)
• [L4] With a follow-up of 97%, about one third of the stabilized shoulders experienced at least one redislocation after 8 to 10 years. [62] (10.1177/0363546511415657)
• [Paper] Short-term outcomes are reassuring, but more research is needed to study long-term graft union, graft resorption, glenohumeral arthritis, and patient outcomes including recurrent shoulder instability. [63] (10.1016/j.eats.2017.10.007)
• [L2] RCTs reporting on shoulder instability surgery are well performed but poorly reported. [64] (10.1177/1758573218754370)
• [L5] [65] (10.1530/eor-24-0025)
• [L3] At mid-term follow-up, patients with a history of anterior shoulder instability undergoing total shoulder arthroplasty can expect continued improvement in function compared with preoperative values. [68] (10.1016/j.jse.2023.07.005)
• [Abstract] The natural history of the first time shoulder dislocations is bound up with arthropathy. [69] (10.1016/j.jse.2007.02.100)
• [L4] The outcomes at 3 years' follow-up were satisfactory in 80% of patients and 86% had stable shoulders. [72] (10.1016/j.otsr.2019.12.009)
• [L3] This long-term follow-up study demonstrated that the open Latarjet procedure is a safe and reliable technique for recurrent anterior shoulder instability. [75] (10.1016/j.jse.2021.03.097)
• [L4] Recent studies continue to demonstrate a role for nonoperative treatment in the successful long-term management of anterior glenohumeral instability. [78] (10.1007/s12178-017-9432-5)
• [L4] [79] (10.1016/j.csm.2004.08.010)
• [L4] Posterior instability represents about 10% of shoulder instability and has become increasingly recognized and treated in military members. [81] (10.1177/1941738116672446)
• [L5] In the interim, surgical soft-tissue stabilization might be more aggressively indicated in cases of primary shoulder dislocation, whereas recurrent instability with bone loss should be referred to experienced high-volume specialists. [82] (10.1016/j.arthro.2016.06.032)
• [L4] Patients undergoing ACRR for recurrent anterior shoulder instability had a recurrent instability rate of 27.6% at a minimum 20-year follow-up. [83] (10.1177/23259671251376528)
• [L4] Arthroscopic capsulolabral repair for posterior shoulder instability was a durable treatment option that improved long-term shoulder pain and function and facilitated return to sport in the majority of patients at a mean follow-up of 15.4 years, although a notable proportion of patients met various criteria for failure. [84] (10.1177/03635465231162271)
• [L4] The glenohumeral joint is inherently predisposed to instability by its bony architecture. [86] (10.1007/s12178-011-9092-9)
• [L4] The recurrence of anterior shoulder instability can be as high as 86.7% in high-risk patients who are treated nonoperatively after their first incident of instability. [88] (10.5435/jaaosglobal-d-19-00168)
• [L5] [89] (10.1016/s0894-1130(12)80078-0)
• [L3] Stabilization of the dominant shoulder resulted in residual surgery-related functional impairments on both sides, whereas stabilization of the nondominant shoulder resulted in impairments primarily noted in the nondominant, operative shoulder. [90] (10.1177/03635465231156181)
• [L3] Patients treated conservatively for anterior shoulder instability were far more likely to achieve a successful outcome defined as completing a subsequent season in their same sport compared to surgical patients. [92] (10.1177/2325967117s00284)
• [L3] [93] (10.1016/s1058-2746(99)90058-7)
• [L5] The system categorizes instability based on frequency, aetiology, direction, and severity. [113] (10.1136/bjsm.2009.071183)
• [L2] Primary non-operative management is a prominent risk factor for recurrence of shoulder instability. [115] (10.1136/bjsports-2016-096895)
• [L1] Shoulder instability cannot reliably be classified using the ICD-9 coding system. [118] (10.1016/j.jse.2008.10.005)
• [L4] To assess the effectiveness of an arthroscopic stabilization procedure for anterior shoulder instability using the Rowe score, a difference of at least 9.7 in the score is clinically relevant. [121] (10.1016/j.jse.2017.10.032)
• [L4] Recurrent anterior instability of the shoulder is a complex disorder which mainly affects younger population, and generally requires surgical intervention to restore joint stability. [123] (10.12998/wjcc.v2.i11.676)
• [L3] In this series of anterior shoulder instability in children and adolescents, instability lesions varied significantly by age, with atypical lesions more common in patients <15 years of age and bone loss associated with older age at presentation. [126] (10.1177/03635465231171129)
• [L2] These findings may represent a pathologic change in the intrinsic characteristics of the shoulder capsule in patients with shoulder instability. [132] (10.1016/j.arthro.2013.07.099)
• [L4] Shoulder instability in female athletes presents commonly as multiple subluxation events. [133] (10.1177/0363546519850810)
• [L5] The success of treating anterior glenohumeral instability relies on multiple factors, including glenoid bone loss. [138] (10.1016/j.arthro.2021.09.002)
• [L1] Primary arthroscopic treatment of posterior shoulder instability is associated with favorable outcomes and high return to sport and work rates. [148] (10.1016/j.asmr.2024.101032)
• [L3] Successful results were obtained in patients younger than 40 years with both primary and recurrent anterior shoulder instability after arthroscopic treatment. [149] (10.1016/j.jse.2023.05.029)
• [L5] The ABC classification distinguishes three groups of posterior glenohumeral instability with two different subtypes based on the pathomechanical type of instability and the current standard of treatment. [150] (10.1007/s11678-017-0404-6)
• [L5] Shoulder Instability: Alternative Surgical Techniques represents a detailed resource that reviews classification of shoulder instability, pathoanatomy, the concept of glenoid track, and evaluation of bone loss and offers a description of various procedures designed to address bone loss and restore stability. [152] (10.1016/j.arthro.2012.09.003)
• [L5] Successful treatment of anterior instability of the shoulder requires a balance between restoring joint stability and minimizing loss of glenohumeral motion. [153] (10.1177/03635465030310011001)
• [L4] Adolescent multidirectional shoulder instability refractory to non-surgical management appears to have long-term outcomes after surgical intervention that are comparable to adolescent patients with unidirectional instability. [155] (10.1177/2325967121s00021)
• [L4] Arthroscopic treatment of posterior shoulder instability is an effective means to improve symptoms associated with recurrent posterior subluxation of the shoulder. [158] (10.1177/0363546505278301)
• [L4] Arthroscopic stabilization of posterior shoulder instability resulted in good outcomes with high patient satisfaction and low rates of recurrent instability, revisions, and residual pain. [163] (10.1016/j.jse.2024.04.006)
• [L4] Current evidence supports the safety and efficacy of both the Latarjet and FBB procedures for anterior shoulder stabilization in the presence of glenoid bone loss. [164] (10.1177/0363546520925833)
• [L2] Arthroscopic surgery is an acceptable treatment if recurrent instability occurs consistently at ≤23.8%. [165] (10.1177/2325967115618161)
• [L3] Nonoperative treatment of shoulder instability has substantial societal costs. [172] (10.1177/1758573218773543)
• [L4] The Latarjet procedure for anterior shoulder instability results in an overall complication rate of 16.1% and a reoperation rate of 2.6%, though serious complications at short-term follow-up appear rare. [173] (10.1177/03635465211042314)
• [L3] Objective and subjective scoring systems correlate significantly with the clinical condition of patients with recurrent shoulder instability and associated bony defects. [180] (10.1177/0363546515626541)
• [L2] Only the WOSI detected differential shoulder function related to shoulder instability. [185] (10.1100/2012/410125)
• [L4] This combination has long-term outcomes in terms of the recurrence rate and does not significantly influence the range of motion of the shoulder. [188] (10.1007/s00167-018-5261-3)
• [Paper] Static MRI does not appear helpful, however CINE MRI can reproducibly confirm the diagnosis of shoulder instability. [191] (10.1016/s1058-2746(96)80178-9)
• [L4] NHL team physicians strongly favor nonoperative management in-season for initial posterior instability events of the shoulder. [193] (10.1177/23259671261440208)
• [L4] Arthroscopic management of a failed instability repair provides similar success to open reconstruction if one selects proper indications. [194] (10.1097/00132589-200212000-00008)
• [L1] Despite the wide array of available PROMs for assessing shoulder instability surgery outcomes, the availability of clinically significant outcome thresholds such as MCID and PASS remains relatively limited. [196] (10.1016/j.arthro.2024.07.039)
• [L4] Recurrent shoulder instability is the most common complication after labral repair, but most reported rates of recurrent instability after arthroscopic Bankart repair are less than 10 %. [201] (10.1007/s12178-014-9248-5)
• [L5] Magnetic resonance arthrography is regarded as the gold-standard imaging modality for shoulder instability. [204] (10.1016/j.mric.2019.12.005)
• [L3] Instability-related complications occurred only in the capsulabral group, and the incidence increased with time. [205] (10.1177/03635465211029022)
• [L3] Surgical shoulder stabilization in an athlete after a first episode of instability is not indicated in all patients. [206] (10.1016/j.arthro.2017.04.088)
• [L4] While recurrence rates increased over time, patient satisfaction remained high, and no revision surgeries were required, demonstrating the long-term reliability of ABR for anterior shoulder instability. [209] (10.1016/j.jseint.2025.07.004)
• [L3] The Bristow-Latarjet procedure was associated with significantly higher rates of full RTS than Bankart repairs in anterior shoulder instability, despite variability in patient indications across procedures. [212] (10.1177/23259671261450204)
• [L5] The authors express caution regarding the consensus that the WOSI should be used as the primary outcome measure for all studies on the treatment of shoulder instability before further prospective, high-level, evidence-based studies and multi-center studies are performed. [213] (10.1177/0363546518765992)
• [L5] Its main indications are for shoulder instability in high-impact athletes, together with a capsule-labrum reconstruction, and poor tissue quality of the labrum in patients with multiple long-term dislocations. [214] (10.1097/bte.0000000000000153)
• [L4] Arthroscopic Bankart repair for anterior shoulder instability has been shown to result in excellent long-term functional outcomes despite a relatively high rate of recurrent instability necessitating revision surgery. [215] (10.1016/j.jse.2019.04.057)
• [L5] In carefully selected patients, the use of anterior and posterior glenoid bone augmentation may be effective as a salvage procedure in rare cases of refractory multidirectional shoulder instability. [219] (10.1097/01.blo.0000150344.74378.b5)
• [Paper] Advanced imaging modalities are essential for identifying associated lesions, and bony reconstruction procedures should be considered for patients with significant glenoid bone loss or recurrent instability after soft tissue reconstruction. [220] (10.1016/j.csm.2014.06.006)
• [L2] Early arthroscopic stabilization by anterior capsule-labrum reinsertion after initial anterior shoulder dislocation is associated with a low 10-year recurrence rate of 35% compared to non-operative management. [221] (10.1016/j.otsr.2015.09.029)
• [L5] [225] (10.1177/1758573218815002)
• [L3] Despite the advantages of MRI in the detection of soft tissue damages in recurrent anterior shoulder instability CT imaging proved to be more important for glenoid defects. [227] (10.1007/s00402-012-1656-7)
• [L4] The iliac posterior shoulder bone-block is effective in managing instances of involuntary posterior shoulder instability, showing satisfactory results in terms of non-recurrence, pain relief, and function recovery. [228] (10.1016/j.otsr.2008.09.008)
• [L4] Adolescent athletes who present with a history of anterior shoulder instability have a high incidence of bipolar bone loss. [229] (10.1177/2325967126s00146)
• [L3] There were no significant racial disparities seen between white and minority patients in regard to the rates of non-operative follow up for anterior shoulder instability. [231] (10.1177/2325967121s00717)
• [L1] [233] (10.2106/jbjs.25.00560)
• [L5] MR-arthrography is identified as the main tool in diagnosing shoulder instability injuries. [234] (10.21037/qims.2017.08.05)
• [L5] [235] (10.1016/j.jisako.2025.101011)
• [L2] [236] (10.1197/j.jht.2004.02.010)
• [L3] About 1 in 3 patients, however, suffered from shoulder instability of whom approximately half reported a redislocation postoperatively. [237] (10.1177/2325967124s00022)
• [L3] [238] (10.1016/j.asmr.2022.07.012)
• [L4] Despite the absence of evidence-based guidelines, there exists minimal variability in recommendations between North American and European shoulder surgeons regarding return to play criteria. [239] (10.1016/j.jse.2021.01.026)
• [L4] These findings suggest that this radiographic change should be regarded as a new sign of anterior shoulder instability of traumatic origin. [241] (10.1016/1058-2746(92)90092-h)
• [L5] [248] (10.1016/s0278-5919(05)70183-6)
• [L3] [249] (10.1097/corr.0000000000002320)
• [L4] In the future, we expect CT to be superseded by MRI in anterior shoulder instability. [251] (10.1016/j.jseint.2025.101440)
• [L4] [252] (10.1016/j.jisako.2025.100765)
• [L4] The radiographic analysis of the Hill-Sachs lesion with a constant, reproducible technique can play a role in the diagnosis of anterior shoulder instability and patient selection for therapeutic intervention. [254] (10.1067/mse.2000.106920)
• [L4] Radiography can be used for screening patients for significant glenoid bone loss. [256] (10.1186/s12891-015-0607-1)
• [L3] The superior-capsular elongation as well as its diagnostic criteria of measurements by MR arthrography revealed in the present study could serve as references for diagnosing atraumatic posteroinferior shoulder instability and offer insight into the spectrum of imaging findings corresponding to the pathologies encountered at clinical presentation. [258] (10.3109/02841850903524421)
• [L4] [259] (10.1007/s00402-015-2193-y)
• [L1] [261] (10.1016/j.arthro.2023.07.010)
• [L1] [262] (10.1016/j.arthro.2018.05.042)
• [L3] ZTE MRI demonstrated high reproducibility for the evaluation of glenoid bone defect in shoulders with anterior instability. [264] (10.1016/j.jseint.2024.03.003)
• [L4] Additionally, MRI is a valid imaging tool to diagnose and measure osseous lesions of the shoulder. [265] (10.1007/s00247-018-4318-2)
• [L4] Arthrotomography of the glenoid labrum is a helpful adjunct in substantiating the diagnosis of shoulder instability and in planning the choice of surgical reconstruction. [266] (10.2106/00004623-198264040-00005)
• [L3] The study investigated whether unstable painful shoulder (UPS) and anterior instability (AI) are associated with differences in scapula morphology using magnetic resonance imaging (MRI). [267] (10.1016/j.jse.2026.04.009)
• [L3] Radiographs seem inferior to CT scans for assessing osseous lesions especially at the glenoid rim. [268] (10.1016/j.jse.2013.04.020)
• [L4] Future studies should attempt to control for all relevant factors, use advanced imaging for glenoid bone loss measurements, and consider a lower predictive threshold for the Instability Severity Index Score. [270] (10.1177/03635465211038712)
• [L4] The swelling and diminished findings of the anteroinferior capsulolabral complex on conventional MRI were moderately related to pathologic arthroscopic findings in patients with traumatic anterior shoulder instability. [271] (10.1016/j.jseint.2024.05.013)
• [L4] MR images did not show the detachment in three shoulders, while arthroscopy proved the detachment in these shoulders. [273] (10.1016/s1058-2746(95)80288-6)
• [L5] Accurate characterization of glenoid and humeral bone loss is essential for preoperative planning to minimize the risk of recurrent dislocation, with three-dimensional imaging serving as an integral component of this evaluation. [274] (10.5435/jaaos-d-22-00016)
• [L4] The number of episodes of dislocation before surgery and the delayed surgical intervention did not increase the recurrent anterior shoulder instability rates postoperatively. [275] (10.1016/j.jseint.2022.12.003)
• [L2] MDCT arthrography showed better accuracy than did MR arthrography in the detection of osseous, cartilage, and labroligamentous injuries related to anterior shoulder instability. [276] (10.2214/ajr.11.7251)
• [L3] In our cohort of young patients undergoing arthroscopic surgery for posterior shoulder instability, we detected no significant difference in reoperation rate and recurrence of symptoms between athletes who underwent objective return to sport testing and those who were released to sport on a time-based protocol. [277] (10.1177/2325967121s00549)
• [L3] In our cohort of young patients undergoing arthroscopic surgery for posterior shoulder instability, we detected no significant difference in reoperation rate and recurrence of symptoms between athletes who underwent objective return to sport testing and those who were released to sport on a time‐based protocol. [278] (10.1177/2325967121s00593)
• [L4] None of the patients has had instability after an average follow-up of 26 months. [279] (10.1016/s1058-2746(97)90064-1)
• [L3] Characteristics related to a history of instability (age <20 years at first instability episode, larger number of dislocations, ≥2 years between first dislocation and surgery) were found to be risk factors for the development of an off-track HS lesion. [280] (10.1177/23259671231213858)
• [L3] The prospective study of an initial series of 29 shoulders with a minimum of 26 months’ follow-up (mean, 36 months) shows 1 poor result because of the recurrence of instability (arthroscopic revision has had a successful outcome), 1 fair result, 2 good, and 25 excellent results (according to the Duplay scale). [281] (10.1097/00132589-200112000-00002)
• [L4] Publication period subgroup analysis suggests that historical instability differences were driven primarily by earlier studies, whereas contemporary studies show comparable instability and functional outcomes between approaches. [282] (10.1177/03635465261443999)

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