Shoulder Instability Info In-depth Evidence

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 Prevalence

• The MOON Shoulder Instability Study has enrolled the largest cohort of patients undergoing shoulder stabilization to date [1].
• Posterior glenohumeral instability accounts for 2% to 5% of all glenohumeral instability [9].
• Up to 50% of traumatic posterior shoulder dislocations are undiagnosed upon presentation to hospital emergency departments [9].
• Multidirectional instability (MDI) is characterized by inferior laxity in addition to anterior and/or posterior laxity [14].

Pathoanatomy

• Traumatic posterior glenohumeral dislocation or recurrent instability can cause posterior labral tearing or disruption of the posterior IGHL [9].
• A compression fracture of the anterosuperior portion of the humeral head, known as a reverse Hill-Sachs, may be present in posterior instability [9].
• Posterior glenoid bone loss may be present in cases of recurrent posterior instability [9].
• In posteriorly unstable shoulders, posterior glenoid depth is significantly reduced in the inferior and middle aspects due to diminished osseous and chondrolabral height [28].
• Two commonly associated anatomic lesions in multidirectional instability are a patulous inferior capsule containing both the anterior and posterior bands of the IGHL and functional deficiency of the rotator interval [14].
• Labral tearing may occur in multidirectional instability with repeated subluxations or a traumatic event [14].

Evaluation

• A history of trauma with the arm locked in internal rotation is characteristic of posterior shoulder instability [9].
• An acute posterior dislocation presents with a prominent posterior shoulder, an anterior coracoid, and limited ability to externally rotate the shoulder [9].
• Posterior instability can lead to compensatory scapular winging [9].
• Specialized tests to assess posterior stability include the posterior stress test and the jerk test [9].
• The posterior stress test is positive if palpable crepitus or subluxation is present when a posterior force is applied through the humerus [9].
• The jerk test involves applying a posterior force along the axis of the humerus with the arm in forward flexion and internal rotation, causing posterior subluxation, followed by a clunk as the arm is brought into extension [9].
• Symptoms of multidirectional instability include pain, weakness, ipsilateral paresthesias, popping or clicking of the shoulder, instability during sleep, difficulty with throwing, and pain when carrying heavy objects [14].
• Differential diagnoses for multidirectional instability include unidirectional shoulder instability, cervical disease, brachial plexitis, and thoracic outlet syndrome [14].
• Assessment for generalized ligamentous laxity using Beighton criteria is part of the physical examination for multidirectional instability [14].
• A positive sulcus sign assesses the competency of the rotator interval in multidirectional instability [14].
• Rotator cuff tendinitis in an individual younger than 20 years should raise concern for multidirectional instability [14].
• Proper evaluation of bone loss best determines shoulder instability surgical indications and outcomes [7].
• MRI is inadequate for detecting combined posterior and anterior instability, which was identified in 40% of operative instability cases in a study by Song et al. [28].

Non-operative Management

• Nonsurgical treatment for posterior shoulder instability should always be attempted first [9].
• 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 [9].
• Long-term follow-up demonstrates that nearly 40% of patients treated non-operatively for posterior shoulder instability eventually require surgery [5].
• At long-term follow-up of 17 years, a high rate of poor outcomes was observed following nonoperative management of anterior shoulder instability [6].
• All patients with multidirectional instability should undergo extensive physical therapy for 6 to 9 months prior to consideration of surgical treatment [14].
• Physical therapy for multidirectional instability should focus on rotator cuff strengthening, scapular kinematics, and proprioceptive training [14].
• Approximately 20% of patients with multidirectional instability fail nonsurgical management [14].
• Many shoulders with posterior instability can be well managed by education, muscle strengthening, and neuromuscular retraining [28].

Operative Management

• Surgical intervention for posterior shoulder instability is indicated for patients with symptoms that interfere with activities or athletics and for failure of nonsurgical management [9].
• Surgery is contraindicated for voluntary dislocators with posterior shoulder instability [9].
• The goal of surgery for posterior shoulder instability is to repair the posterior capsulolabral structures and to re-tension the posterior capsule to prevent recurrent instability [9].
• Soft-tissue procedures for posterior shoulder instability include open or arthroscopic labral repair and posterior capsular shift [9].
• Some authors recommend plication of the rotator interval for posterior shoulder instability, though this is controversial [9].
• Options for an engaging reverse Hill-Sachs include structural bone graft to the humeral head, the McLaughlin or modified McLaughlin procedure, or resurfacing arthroplasty [9].
• Options for posterior glenoid bone loss include distal tibial allograft or autograft reconstruction using the posterior acromion, iliac crest, or distal clavicle [9].
• The 1-year outcomes in a prospective study suggest superiority of operative over non-operative treatment for posterior shoulder instability [8].
• 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 [121].
• In a prospective cohort 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 [28].
• In the adolescent population, 92% of patients who underwent posterior capsulolabral repair were stable at 5 years follow-up [28].
• Arthroscopic techniques for posterior instability repair have shown promising results that are generally more favorable than those after anterior instability repair [28].
• Surgical stabilization of posterior glenohumeral instability may be considered when recurrent involuntary posterior subluxation or dislocation occurs despite a concerted effort at a well-structured rehabilitation program [28].
• Before surgery for posterior instability, it is essential to identify all directions of instability and anatomic factors such as humeral head or glenoid defect, abnormal glenoid version, rotator cuff tears, neurologic injuries, or generalized ligamentous laxity [28].
• Surgery for multidirectional instability is appropriate for patients with pain and instability that interferes with normal or sport-related activity who have failed extensive nonsurgical treatment [14].
• Surgery is contraindicated for voluntary dislocators and patients who have not attempted physical therapy for multidirectional instability [14].
• Arthroscopic pancapsular plication with or without rotator interval closure is a surgical technique for multidirectional instability [14].
• If labral pathology is encountered during surgery for multidirectional instability, anterior or posterior labral repair is indicated [14].
• Capsulorrhaphy for multidirectional instability should address the inferior redundancy in a balanced fashion to avoid asymmetric tightening [14].
• Open anterior-inferior capsular shift is a surgical technique for multidirectional instability [14].
• Free bone block procedures are considered safe and clinically effective for the management of anterior shoulder instability with glenoid bone loss [21].
• 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% [30].

Complications and Outcomes

• Recurrence is the most common complication of posterior shoulder instability surgery, reported at 8.5% in the general population [9].
• Recurrence rates for posterior shoulder instability are highest in overhead athletes [9].
• Recurrence rates for posterior shoulder instability increase with posterior glenoid bone loss greater than 20%, which should be considered a contraindication to arthroscopic soft-tissue stabilization alone [9].
• Shoulder stiffness or adhesive capsulitis is a concern with rotator interval plication for posterior shoulder instability [9].
• Overtightening of the posterior capsule can lead to anterior subluxation or coracoid impingement [9].
• Recurrence of multidirectional instability is reported at 7% for both open and arthroscopic techniques [14].
• Axillary nerve injury is a complication of multidirectional instability surgery [14].
• Stiffness is a rare complication of multidirectional instability surgery [14].
• Subscapularis insufficiency is a complication after open procedures for multidirectional instability [14].
• A notable proportion of patients undergoing arthroscopic capsulolabral repair for posterior shoulder instability met various criteria for failure at long-term follow-up [121].
• The pooled published rate of return to any sport after posterior shoulder instability surgery is 91% [9].
• The pooled published rate of return to preinjury level of sport after posterior shoulder instability surgery is 67% [9].

Rehabilitation and Follow-up

• Postoperatively, the shoulder should be placed in a rigid immobilizer with the arm abducted to 30° in neutral rotation [9].
• Range of motion exercises may begin after a short period of immobilization following posterior shoulder instability surgery [9].
• Strengthening should begin at 12 weeks following posterior shoulder instability surgery [9].
• Patients may return to heavy labor or contact sports 6 months after posterior shoulder instability surgery [9].
• The Western Ontario Shoulder Instability Index (WOSI) is recommended for following up patients with shoulder instability [33].
• 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 [25].
• The availability of clinically significant outcome thresholds such as MCID and PASS for shoulder instability surgery remains relatively limited [120].

Anatomy & Pathophysiology

Definitions and Classification

• Instability is defined as a patient experiencing symptoms of a shoulder problem, whereas asymptomatic shoulders with increased joint translation are defined as lax [38].
• The Gerber classification distinguishes multidirectional instability from multidirectional hyperlaxity, noting that hyperlaxity is an individual constitutional trait rather than a primary disease [29].
• The Gerber classification categorizes shoulder instability into six groups: 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 [29].
• The ABC classification distinguishes three groups of posterior shoulder instability based on the nature of pathology (first-time, dynamic, or static) and two subtypes based on pathomechanical causes [34].
• Static instabilities are defined by the absence of classic symptoms of instability yet a fixed displacement of the humeral head superior, anterior, or posterior relative to its normal position on the glenoid fossa [29].
• Static instabilities are diagnosed radiologically rather than clinically and may remain asymptomatic for a long period [29].
• Static instabilities can co-exist with dynamic instabilities, in which case the more disabling instability is usually dynamic and is best treated initially [29].
• The TUBS acronym describes traumatic etiology, unidirectional instability, Bankart ligamentous detachment, and surgical repair [38].
• The AMBRI acronym describes atraumatic etiology, multidirectional instability, bilateral shoulders, rehabilitation with rotational strengthening, and inferior capsular tightening [38].
• Pain is the more common symptom with shoulder instability based on ligamentous laxity (AMBRI), whereas apprehension is more common with unidirectional traumatic instability (TUBS) [38].

Bony Anatomy

• The glenoid is a convex structure of shallow depth shaped like an inverted pear that articulates with the humeral head and serves as the attachment for the labrum and joint capsule [50].
• The subchondral bone of the glenoid is relatively flat, with the articular concavity augmented by cartilage and a circumferential labrum [52].
• The glenoid averages 5° of retroversion in relation to the axis of the scapular body [52].
• The humeral head is spherical with a diameter of 37 to 57 mm [50].
• The humeral head averages 19° of retroversion and 41° of inclination (neck-shaft angle) [52].
• The neck-shaft angle measures an average of 135 degrees, and the humeral head is retroverted an average of 30 degrees [51].
• The articular head is spherical and has a diameter of 37 to 57 mm, with the most superior portion of the articular surface averaging 8 mm above the greater tuberosity [50].
• The humeral version averages 29.8 degrees with a range of 10 to 55 degrees [50].
• The head is inclined approximately 130 degrees with respect to the humeral shaft [50].
• The glenoid cavity is a shallow socket, approximately one third the size of the humeral head [51].
• The proximal humerus contains the humeral head, lesser and greater tuberosities, bicipital groove, and proximal humeral shaft [51].
• The anatomic neck of the proximal humerus is located at the junction of the articular surface and the tuberosities [50].
• The surgical neck represents an indistinct region below the tuberosities but above the humeral shaft [50].
• The greater tuberosity is located in a posterior-superior location with respect to the humeral shaft and serves as the attachment site for the supraspinatus, infraspinatus, and teres minor tendons [50].
• The lesser tuberosity is located on the anterior aspect of the proximal humerus and serves as the attachment site for the subscapularis tendon [50].
• The bicipital groove lies between the greater and lesser tuberosities and serves as a pathway for the long head of the biceps [50].
• The distal aspect of the bicipital groove is internally rotated with respect to the proximal portion [50].
• The acromion, coracoacromial ligament, and coracoid process form the coracoacromial arch, a rigid bony-ligamentous structure that imparts stability to the shoulder girdle [50].
• The superior shoulder suspensory complex (SSSC) provides a stable connection between the scapula and the axial skeleton [52].
• The SSSC is composed of the glenoid, coracoid process, coracoclavicular ligaments, distal clavicle, acromioclavicular joint, and acromion [52].
• The superior strut of the SSSC comprises the middle clavicle, and the inferior strut comprises the lateral scapular border or spine of the scapula [52].
• The proximal humerus receives its blood supply from the anterior and posterior humeral circumflex branches from the third division of the axillary artery [50].
• The anterior humeral circumflex artery provides vascular inflow to the humeral head by way of its terminal anterolateral branch known as the artery of Laing or arcuate artery [50].
• The ascending branch of the anterior humeral circumflex artery courses parallel to the lateral aspect of the long head biceps tendon and enters the humeral head at the interface of the bicipital groove and greater tuberosity [50].
• Injury to the arcuate artery may result in osteonecrosis of the humeral head [50].
• Additional extraosseous collateral branches can permit humeral head perfusion despite complete ligation of the arcuate artery [50].
• The anterolateral ascending branch of the anterior humeral circumflex artery provides the primary blood supply to the humeral head [52].
• The terminal intraosseous portion of the anterior humeral circumflex artery enters at the proximal aspect of the intertubercular groove as the arcuate artery [52].
• Fractures of the anatomic neck have a poor prognosis because of complete disruption of the blood supply to the head [51].
• Surgical neck fractures are common, and with these, the blood supply to the head is preserved [51].

Soft Tissue Anatomy and Ligaments

• The rotator cuff consists of four muscles: the subscapularis, supraspinatus, infraspinatus, and teres minor [51].
• The teres major is not a rotator cuff muscle [51].
• The cuff muscles serve as depressors of the humeral head to allow the deltoid to efficiently abduct the humerus [51].
• The infraspinatus and teres minor are external rotators, while the subscapularis is an internal rotator of the humerus [51].
• The subscapularis is the largest and strongest of the rotator cuff tendons [106].
• The subscapularis is responsible for active internal rotation of the humerus and contributes to the stability of the shoulder [106].
• The subscapularis forms the anterior portion of the transverse plane "force couple" of the rotator cuff and serves to balance forces generated across the joint to maintain glenohumeral congruency [106].
• The rotator interval is defined medially by the base of the coracoid, superiorly by the supraspinatus tendon, and inferiorly by the subscapularis tendon [52].
• The rotator interval contains the coracohumeral ligament, the superior glenohumeral ligament, and the intra-articular portion of the long head of the biceps tendon [52].
• Laxity of the rotator interval results in inferior laxity (the sulcus sign) [52].
• Contracture of the rotator interval is seen with adhesive capsulitis [52].
• The coracohumeral ligament restricts external rotation in adduction and is a static restraint to inferior and posterior translation in adduction and external rotation [52].
• The superior glenohumeral ligament is a primary static restraint against anterior translation with the arm at the side [52].
• With the coracohumeral ligament, the superior glenohumeral ligament forms a pulley that provides restraint against medial subluxation of the long head of the biceps tendon [52].
• The middle glenohumeral ligament is a primary static restraint against anterior translation with the arm in external rotation and 45° of abduction [52].
• The anterior band of the inferior glenohumeral ligament is a primary static restraint against anterior-inferior dislocation of the glenohumeral joint in 90° of abduction and external rotation [52].
• The posterior band of the inferior glenohumeral ligament is a primary static restraint against posterior-inferior translation in internal rotation and adduction [52].
• The glenoid labrum provides concavity and up to 50% of marginal glenoid socket depth [52].
• The subscapular bursa lies between the subscapularis tendon and the neck of the scapula and communicates with the joint cavity between the superior and middle glenohumeral ligaments [53].
• The subscapular bursa protects the tendon of the subscapularis at the point where it passes under the base of the coracoid process and over the neck of the scapula [53].
• The subscapular bursa often houses loose bodies in the shoulder and is a region in which synovitis of the shoulder may be most intense [53].
• In 28% of specimens dissected by Colas and colleagues, the subscapular bursae merged with the subcoracoid bursae, forming a unique wide bursa [53].
• DePalma described six common variations or types of recesses in the anterior capsule, which are variations in the opening of the subscapularis bursa [53].
• Type 1 recesses (30.2%) have one synovial recess above the middle glenohumeral ligament [53].
• Type 2 recesses (2.0%) have one synovial recess below the middle glenohumeral ligament [53].
• Type 3 recesses (40.6%) have one recess above and one below the middle glenohumeral ligament [53].
• Type 4 recesses (9.0%) have one large recess above the inferior ligament, with the middle glenohumeral ligament being absent [53].
• Type 5 recesses (5.1%) have the middle glenohumeral ligament manifested as two small synovial folds [53].
• Type 6 recesses (11.4%) have no synovial recesses, although all the ligaments are well defined [53].
• DePalma believed that if the capsule arises at the labrum or glenoid border of the scapula, few, if any, recesses would be present [53].
• If the capsule begins farther medially on the scapula or glenoid neck, the synovial recesses are larger and more numerous [53].
• DePalma believed that the end result of such recesses was a thin, weakened anterior capsule that could predispose the shoulder to instability [53].
• Plancher and colleagues found the average area of the rotator interval to be 20.96 mm [53].
• Dynamic testing has shown that the subscapularis and supraspinatus dimensions as well as the total area of the rotator interval decrease significantly with internal rotation and open with external rotation [53].
• Imbrication procedures are performed with the arm in a neutral position to avoid loss of motion or insufficient tightening [53].
• A soft tissue sheath consistently covers the long head of the biceps tendon to the level of the proximal margin of the pectoralis major tendon and contributes to the roof of the bicipital tunnel [53].
• The fibro-osseous bicipital tunnel consists of three distinct anatomic zones [53].
• Zone 1 of the bicipital tunnel represents the traditional bony bicipital groove beginning at the articular margin and ending at the distal margin of the subscapularis tendon [53].
• Zone 2 of the bicipital tunnel extends from the distal margin of the subscapularis tendon to the proximal margin of the pectoralis major tendon and represents a "no man's land" because it is not viewable from arthroscopy above or from subpectoral exposure below [53].
• Zone 3 of the bicipital tunnel is distal to the proximal margin of the pectoralis major tendon and represents the subpectoral region [53].
• The superior transverse scapular ligament arises from the medial base of the coracoid overlying the suprascapular notch [52].
• The suprascapular artery runs superior to the superior transverse scapular ligament, and the nerve runs deep to the ligament [52].
• Entrapment of the suprascapular nerve at the superior transverse scapular ligament causes denervation of both the supraspinatus and the infraspinatus [52].
• The spinoglenoid ligament overlies the suprascapular nerve at the spinoglenoid notch [52].
• Entrapment, traction, or compression of the suprascapular nerve at the spinoglenoid notch causes denervation of the infraspinatus [52].

Pathophysiology and Mechanisms

• The shoulder depends on dynamic and static stabilizers because it has little inherent stability, making it prone to instability [103].
• External loads transferred to the shoulder girdle are initially offset by joint surface anatomy, joint volume, atmospheric pressure, and joint fluid cohesion and adhesion [50].
• Moderate and large loads are counterbalanced by the deltoid and rotator cuff and by the capsulolabral and bone structures, respectively [50].
• The limited joint volume effect is reduced if the joint is vented (opened to the atmosphere) or if the capsular boundaries of the joint are very compliant [154].
• Gibb et al. found that simply venting the capsule with an 18-gauge needle reduced the force necessary to translate the head of the humerus halfway to the edge of the glenoid by an average of 50% [154].
• Wulker et al. found that venting the joint increased displacement of the joint with an applied load of 50 N by 50% in all directions [154].
• Glenohumeral stability from limited joint volume is compromised by arthrography, arthroscopy, articular effusions, hemarthrosis, and other situations in which free fluid is allowed to enter the glenohumeral joint [154].
• Habermeyer et al. found that the mean stabilizing force obtained by atmospheric pressure was 146 N (32 lb) [154].
• In 15 stable, living shoulders, traction on the arm caused negative intra-articular pressure proportionate to the amount of force exerted [154].
• Unstable shoulder joints with a Bankart lesion did not exhibit the phenomenon of negative intra-articular pressure caused by traction [154].
• Capsular laxity is the essential lesion in multidirectional instability [27].
• Increased capsular volume and cross-sectional area are nonspecific findings common to many patients with capsular laxity and recurrent instability [27].
• Injury to the rotator interval is an important component of anterior capsular injury in general [27].
• Shallow glenoid morphology has been identified as a contributing factor in some cases of multidirectional instability [27].
• Voluntary dislocators with a component of natural laxity and untreated skeletal dyskinesia can become involuntary dislocators with labral tears or capsular pathology [27].
• Patients who are "born loose" may become patients who are "worn loose" or "torn loose" [27].
• In patients with loose shoulders, the collagen fibers in the capsule, muscles, and skin are relatively immature, more soluble, and less cross-linked than those in controls [154].
• Tissues such as the glenoid labrum contain immature collagen as well, making them more deformable under load but less likely to tear [154].
• A positive family history of shoulder instability was found in 24% of patients who required surgery for anterior glenohumeral instability [154].
• A positive family history was reported in approximately 15% of patients who were operated on for recurrent anterior shoulder instability [154].
• A positive family history was noted twice as often in patients whose postoperative course was complicated by recurrent instability [154].
• Traumatic posterior glenohumeral dislocation or recurrent instability can cause posterior labral tearing or disruption of the posterior inferior glenohumeral ligament [9].
• A compression fracture of the anterosuperior portion of the humeral head (a reverse Hill-Sachs) may be present in posterior instability [9].
• There are two commonly associated anatomic lesions in multidirectional instability: a patulous inferior capsule which contains both the anterior and posterior bands of the inferior glenohumeral ligament and functional deficiency of the rotator interval [14].
• Labral tearing may occur with repeated subluxations or a traumatic event in multidirectional instability [14].
• Basic science research findings have played an integral role in improving the understanding of the role of the capsuloligamentous complex in shoulder

Classification

Historical and General Systems

• Since the 1980s, 18 classifications have been developed to define sub-groups of shoulder instability, but none have demonstrated strong measurement properties [4].
• Rockwood distinguished shoulder instabilities based on the presence or absence of trauma in 1979 [4].
• The Thomas and Matsen classification introduced the AMBRI acronym for atraumatic multidirectional instability, which is often bilateral and requires rehabilitation and inferior capsular shift [4].
• The Thomas and Matsen classification introduced the TUBS acronym for traumatic unidirectional instability, which is associated with a Bankart lesion and often requires surgery [4].
• The Stanmore classification was introduced in 2004 to encompass Polar type I (true TUBS, traumatic, structural), Polar type II (true AMBRI, atraumatic, structural), and Polar type III (atraumatic with functional origin due to muscle patterning disorders or habitual non-structural) [4].
• The Stanmore classification also encompasses presentations of instability that combine multiple categories [4].
• A 2004 classification system challenges previous systems by being all-inclusive and recognizing that more than one pathology can occur in an individual shoulder [3].
• The FEDS classification categorizes instability based on frequency, aetiology, direction, and severity [63].
• 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 [24].
• Shoulder instability cannot reliably be classified using the ICD-9 coding system [71].
• The Western Ontario Shoulder Instability Index study classified patient demographics according to the Frequency, Etiology, Direction, and Severity classification system [145].

Gerber Classification

• The Gerber classification distinguishes multidirectional instability from multidirectional hyperlaxity because hyperlaxity is an individual constitution rather than a primary disease [29].
• The Gerber classification includes chronic locked dislocation as a category [29].
• The Gerber classification includes unidirectional instability without hyperlaxity as a category [29].
• The Gerber classification includes unidirectional instability with hyperlaxity as a category [29].
• The Gerber classification includes multidirectional instability without hyperlaxity as a category [29].
• The Gerber classification includes multidirectional instability with multidirectional hyperlaxity as a category [29].
• The Gerber classification includes uni- or multidirectional voluntary instability as a category [29].
• In the Gerber classification, 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 [29].
• Static instability in the Gerber classification is diagnosed radiologically, not clinically [29].
• Static instabilities in the Gerber classification may remain asymptomatic for a long period [29].
• Static instabilities in the Gerber classification can co-exist with dynamic instabilities [29].
• Class A1 static superior subluxation is defined by a decreased distance between the undersurface of the acromion and the most cranial aspect of the humeral head on an AP radiograph with the shoulder in neutral rotation [29].
• Seven millimetres is the value used to define static superior subluxation in Class A1 [29].
• The cause of cranial migration in Class A1 static superior subluxation seems to be insufficiency of the infraspinatus in the presence of a supraspinatus tear [29].
• Isolated supraspinatus, isolated infraspinatus, or combination tears of the supraspinatus and subscapularis tendons do not cause static superior instability [29].
• Loss of the acromiohumeral distance to less than 7 mm is associated with loss of strength of abduction and external rotation [29].
• Static superior subluxation carries a poor prognosis for repair of the rotator cuff tear and is considered a predictor of an irreparable tear [29].
• Superior static subluxation is essentially irreversible by conventional repair techniques [29].
• Class A2 static anterior subluxation is a fixed anterior position of the humeral head on the glenoid fossa [29].
• Class A2 static anterior subluxation is often manifest clinically as moderate to severe shoulder pain caused by impingement under the coracoid and coracoacromial arch and loss of anterior elevation [29].
• Class A2 static anterior subluxation is usually detected on CT scans or MRI scans taken with the arm in neutral rotation but occasionally may be evident on axillary lateral radiographs [29].
• Class A2 static anterior subluxation usually is not associated with recurrent anterior shoulder instability [29].
• To develop a static anterior subluxation without any previous operation, a combination of a subscapularis tear, a supraspinatus tear, and fatty degeneration of the infraspinatus muscle seems necessary [29].
• An isolated tear of the subscapularis tendon and posterosuperior tears usually do not lead to anterior static subluxation [29].
• Static anterior subluxation has been irreversible with soft tissue procedures [29].
• Class A3 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 [29].
• Class A3 static posterior subluxation is most frequently but not always associated with congenital dysplasia of the glenoid or with degenerative glenohumeral joint disease [29].
• Class A3 static posterior subluxation may be associated with glenoid deformations such as those classified by Walch and co-workers [29].
• Class A3 static posterior subluxation may be present without any rotator cuff deficiencies [29].
• Most authors have found static posterior subluxations to be irreversible [29].
• Class A4 inferior subluxation of the shoulder is characterized by straight inferior translation of the humerus relative to the glenoid fossa [29].
• Inferior subluxation may occur from trauma, neurologic injury, septic arthritis, or inadequate restoration of humeral length after arthroplasty [29].
• Inferior subluxation after trauma and surgery, if not associated with permanent nerve injury, usually resolves within 6 weeks but always resolves within 2 years [29].
• Inferior subluxation caused by infection tends to result in joint surface destruction and only successful treatment of infection results in resolution of the inferior subluxation [29].
• Inferior subluxation caused by neurologic injury or shortening of the humerus remains symptomatic unless the primary problem can be resolved [29].

Posterior Shoulder Instability (ABC Classification)

• The ABC classification distinguishes three groups of posterior shoulder instability based on the nature of pathology: first-time, dynamic, or static [34].
• The ABC classification includes two different subtypes for each of the three groups based on pathomechanical causes [34].
• The ABC classification aims to facilitate diagnosis and assist the treatment decision-making process for posterior shoulder instability [34].
• 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 [95].
• An international expert Delphi consensus statement recommends that posterior shoulder instability be classified by the ABC classification [44].

Bone Defects and Pathology

• There are different patterns of subcritical bipolar bone lesions in anterior shoulder instability that can be divided into 4 groups with significantly different prevalence [150].
• Subcritical bipolar bone lesion patterns are significant predictors of failure after surgery for anterior shoulder instability [150].
• Surgeons should be aware that additional procedures may be considered depending on a specific pattern of subcritical bipolar bone lesion [150].
• 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].

Clinical Presentation

Definitions and Classification

• Shoulder instability is defined as a patient experiencing symptoms of a shoulder problem, whereas asymptomatic shoulders with increased joint translation are defined as lax [38].
• Non-traumatic shoulder instability (NTSI) is defined as abnormal movement or position of the shoulder leading to pain, subluxation, or dislocation without a significant history of injury [4].
• The AMBRI classification describes atraumatic multidirectional instability that is often bilateral and requires rehabilitation and inferior capsular shift [4].
• The TUBS classification describes traumatic unidirectional instability associated with a Bankart lesion that often requires surgery [4].
• The Stanmore classification encompasses Polar type I (true TUBS), Polar type II (true AMBRI), and Polar type III (atraumatic with functional origin due to muscle patterning disorders or habitual non-structural instability) [4].
• Multidirectional instability is defined as instability in all three directions: anterior, posterior, and inferior [27].
• True multidirectional instability, where translations are symptomatic in all directions, is uncommon [27].
• A proposed classification system challenges previous systems by being all-inclusive and recognizing that more than one pathology can occur in an individual shoulder [3].

History Taking

• The history should define the mechanism of injury, including the position of the arm, the amount of force applied, and the point of force application [89].
• Injury with the arm in extension, abduction, and external rotation favors anterior dislocation [89].
• Electoshock, seizures, or a fall on the flexed and adducted arm are commonly associated with posterior dislocation [89].
• For recurrent instability, the history should define the initial injury, the position or action resulting in instability, how long the shoulder stays out, and what means were necessary to reduce the shoulder [89].
• The history should note the age at first dislocation, increasing ease of dislocation, frequency of recurrence, duration of symptoms, and the patient's ability to reduce the dislocation themselves [87].
• A history of trauma with the arm locked in internal rotation is characteristic of posterior glenohumeral instability [9].
• Volitional dislocation of the shoulder must be ruled out in the history for posterior instability [9].
• Patients with a sense of slipping and looseness without macrotrauma often present with nondescript discomfort and diffuse pain around the shoulder girdle that is poorly localized and may be more scapular in location [38].
• The association of symptoms with paresthesia down the arm is nearly always related to shoulder instability [38].
• True symptomatic multidirectional instability is typically symptomatic in midrange positions before ligament tension reaches the end of its range [38].
• The classic patient with traumatic instability is a male athlete who sustained an identifiable traumatic event during violent activity [38].
• The classic patient with multidirectional shoulder instability is a young, asthenic female ballet dancer, swimmer, or volleyball player with nondescript shoulder pain involving the scapula and provoking paresthesia down the arm in the absence of a defined traumatic event [38].
• Posterior shoulder dislocation is a rare and challenging injury with varied mechanisms of trauma that complicate diagnosis [22].
• Recurrent posterior shoulder instability is an uncommon condition often unrecognized, leading to incorrect diagnoses and delays [15].
• Microinstability can be diagnosed in young patients with ambiguous shoulder pain during motion, without instability [72].
• Minor shoulder instability is an intra-articular pathology presenting with extra-articular subacromial impingement symptoms [69].

Physical Examination: General and Anterior

• The apprehension-relocation test (Fowler test) is the most sensitive test for anterior instability, where the arm is placed into abduction and external rotation to elicit a sense of instability that is relieved by a posterior force [87].
• The load-and-shift test classifies degrees of instability based on the distance of humeral head translation: 1+ is 0 to 1 cm of translation to before the glenoid rim, 2+ is 1 to 2 cm of translation to the glenoid rim, and 3+ is greater than 2 cm translation or over the glenoid rim [87].
• An evaluation of generalized laxity should be performed during physical examination [87].
• An acutely dislocated shoulder is usually very painful with muscles in spasm, and the humeral head may be palpable anteriorly [89].
• The posterior and lateral aspect of an anteriorly dislocated shoulder shows a hollow beneath the acromion, and the arm is held in slight abduction [89].
• Assessment of the neurovascular status of the upper extremity is an essential part of the physical examination of an anteriorly dislocated shoulder before reduction [89].
• Patients with multidirectional instability may exhibit positive anterior and posterior apprehension, a pathologic sulcus sign with no history of trauma, and no history of dislocation requiring reduction [27].
• Multidirectional instability is characterized by generalized ligamentous laxity as well as abnormal shoulder and scapular kinematics [27].
• The contralateral shoulder in patients with multidirectional instability may exhibit many of the same characteristics but may or may not be symptomatic [27].
• A thorough clinical examination must include passive and active range of motion, usually after 6 weeks, and both shoulders should be evaluated and compared [65].
• Risk factors associated with treatment failure include age, gender, presence of osseous Bankart, large Hill-Sachs lesions, participation in competitive collision or forced overhead sports, hypermobility, time lapse between dislocation and reduction, and the number of instability episodes prior to operation [85].
• An examination under anesthesia is critical for determining the degree and direction of instability without being affected by patient apprehension or guarding [85].
• The axial load test or load-and-shift test is conducted during examination under anesthesia to note translation in the anterior, inferior, and posterior directions [85].
• Grade 1+ instability corresponds to translation of the humeral head to the edge of the glenoid, 2+ if the humeral head can be subluxated over the glenoid rim but reduces spontaneously, and 3+ if a frank dislocation does not reduce spontaneously [85].

Physical Examination: Posterior

• An acute posterior dislocation presents with a prominent posterior shoulder and anterior coracoid and a limited ability to externally rotate the shoulder [9].
• The jerk test involves applying a posterior force along the axis of the humerus with the arm in forward flexion and internal rotation, causing posterior subluxation, followed by a clunk as the arm is brought into extension and the humerus reduces [9].
• Classic features of a posterior dislocation include limited external rotation (often to <0 degrees), limited elevation (often to <90 degrees), posterior prominence and rounding of the shoulder, flattening of the anterior aspect of the shoulder, and prominence of the coracoid process [89].
• Asymmetry of shoulder contours in posterior dislocation can often best be visualized by viewing the shoulders from above while standing behind the patient [89].
• Motion is limited in posterior dislocation because the humeral head is fixed on the posterior glenoid rim by muscle forces or impaled on the glenoid rim [89].
• Patients with old, unreduced posterior dislocations can have 30 to 40 degrees of glenohumeral abduction and some humeral rotation as a result of enlargement of the groove [89].
• Long-standing disuse of muscles about the shoulder in posterior dislocation leads to atrophy that accentuates the flattening of the anterior portion, prominence of the coracoid, and fullness of the posterior portion [89].
• Posterior dislocation may be misdiagnosed as a frozen shoulder during the interval before diagnosis is made [89].

Imaging and Diagnostic Work-up

• Many different diagnostic examinations for assessing shoulder instability are used, with a high variety seen in the use of diagnostic tools [11].
• MRI has proven useful in identifying capsulolabral avulsions (HAGL and reverse HAGL lesions) and rotator cuff pathology, which is common in patients over 40 years old with glenohumeral dislocation [85].
• Plain radiography is able to capture substantial bone loss on the glenoid and humerus, while computed tomography (CT) allows for more precise quantification of bone loss [85].
• The best CT views to evaluate the glenoid are sagittal cuts and three-dimensional (3D) reconstructed en face glenoid views with the humerus subtracted [85].
• A 1.5-mm osseous lesion corresponds to 5% glenoid bone loss [85].
• Glenoid bone loss greater than 18% to 25% of the glenoid surface area increases the risk of failure of nonoperative and operative management that does not address the bone loss [85].
• Recent analysis suggests 18% bone loss as the threshold for concern in combined glenoid and humeral head bone loss (bipolar lesions) [85].
• Identification of critical radiographic variables on magnetic resonance arthrography assists in the accurate diagnosis and management of clinically significant posterior shoulder instability [18].
• 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].
• Arthroscopic inspection of the intra-articular and bursal surfaces of the rotator cuff should be performed, particularly in older patients who tend to have a high prevalence of concomitant rotator cuff pathology [85].
• Approximately 20% to 25% of patients with instability undergoing arthroscopy have associated loose bodies, rotator cuff tears, biceps tendon pathology, or SLAP lesions [85].
• Diagnostic arthroscopy is critical for finalizing the surgical plan and includes evaluation of the glenoid labrum, capsular redundancy, tissue quality, size of the humeral Hill-Sachs defect, anterior-inferior bony defects of the glenoid, osteochondral loose bodies, and glenohumeral ligament detachment [85].
• Detachment or tearing of the glenoid labrum can confirm the presence and indicate the direction of the dominant instability vector [85].
• Traumatic shoulder instability in patients older than 35 years may result in a wide array of pathologic findings as well as a diversity of clinical presentations [58].
• 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 [60].

Investigations

Plain Radiography and CT

• Standardized plain films are almost always sufficient to garner the information needed for shoulder evaluation [16].
• The anteroposterior (AP) view in the plane of the scapula shows the superoinferior position of the humeral head relative to the glenoid, presence of osteophytes, joint space narrowing, and degree of medial displacement of the humerus [16].
• The axillary view taken with the arm in the functional position of elevation is referred to as the "truth view" because it demonstrates glenohumeral relationships in the functional position [16].
• The standardized axillary view enables the measurement of posterior subluxation or "functional decentering" that is not evident in images taken with the arm at the side [16].
• CT scans may offer increased precision in the measurement of glenoid version, but this precision does not necessarily improve the quality of surgery or clinical outcome [16].
• 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 [83].
• CT imaging proved to be more important than MRI for glenoid defects in recurrent anterior shoulder instability [131].
• Radiography can be used for screening patients for significant glenoid bone loss [152].
• Advanced imaging modalities are essential for identifying associated lesions in shoulder instability [125].

Magnetic Resonance Imaging (MRI) and Arthrography

• MRI is the modality of choice for evaluating the rotator cuff, biceps, and subacromial/subdeltoid bursa [83].
• 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 [83].
• T2-weighted MRI provides better visualization of full thickness rotator cuff tears [83].
• MR arthrography is considered the benchmark for evaluation of labral tears [83].
• MR arthrography is identified as the main tool in diagnosing shoulder instability injuries [139].
• Magnetic resonance arthrography is regarded as the gold-standard imaging modality for shoulder instability [123].
• Superior-capsular elongation and its diagnostic criteria of measurements by MR arthrography can serve as references for diagnosing atraumatic posteroinferior shoulder instability [153].
• Zero echo time (ZTE) MRI demonstrated high reproducibility for the evaluation of glenoid bone defect in shoulders with anterior instability [156].
• MRI is a valid imaging tool to diagnose and measure osseous lesions of the shoulder in adolescents [157].
• Regardless of the radiologist interpretation of MRA, patients with symptomatic posterior shoulder instability do benefit from arthroscopic stabilization surgery [41].
• In the future, CT is expected to be superseded by MRI in anterior shoulder instability [146].

Ultrasonography and Other Modalities

• Ultrasonography is a low-cost alternative to MRI and arthrography for evaluating both skeletal and soft-tissue structures of the shoulder [83].
• Ultrasonography can provide immediate, real-time visualization of the rotator cuff, biceps tendon, and calcific deposits [83].
• Ultrasonography can be used to measure the subacromial space and detect atrophy of rotator cuff muscles [83].
• 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 [83].
• Arthrotomography of the glenoid labrum is a helpful adjunct in substantiating the diagnosis of shoulder instability and in planning the choice of surgical reconstruction [158].

Diagnostic Variability and Clinical Context

• Substantial variability was observed in the scoring of important elements in the radiological report for the evaluation of anterior shoulder instability, regardless of modality [136].
• The MOON Shoulder Instability group focuses on patients undergoing surgical treatment for shoulder instability and has described baseline demographics, modifying factors, and limited early outcomes [2].

Treatment

Non-Operative Management

• All patients with multidirectional instability (MDI) should undergo extensive physical therapy for 6 to 9 months prior to consideration of surgical treatment [14].
• Physical therapy for MDI should focus on rotator cuff strengthening, scapular kinematics, and proprioceptive training [14].
• Approximately 20% of patients with MDI fail nonsurgical management [14].
• Surgery for MDI is contraindicated for voluntary dislocators and patients who have not attempted physical therapy [14].
• For atraumatic shoulder instability, physiotherapy should always be the primary management strategy whether there is structural pathology or not [129].
• Eighty per cent of patients with atraumatic shoulder instability should respond to non-operative measures [129].
• Primary non-operative management is a prominent risk factor for recurrence of shoulder instability in young and adolescent athletes [66].
• Most patients younger than 40 years with shoulder instability who were initially treated nonoperatively for 6 months were definitively treated without surgery [46].
• Nonoperative treatment of shoulder instability has substantial societal costs [109].
• NHL team physicians strongly favor nonoperative management in-season for initial posterior instability events of the shoulder [119].
• Recent studies continue to demonstrate a role for nonoperative treatment in the successful long-term management of anterior glenohumeral instability [117].
• The cornerstone of treatment for instability remains immobilization followed by rehabilitation [26].
• For patients with atraumatic multidirectional instability (AMBRI), most cases can be managed nonoperatively by patient education and rehabilitation [13].

Operative Management: Indications and Contraindications

• Surgical intervention for posterior shoulder instability is indicated for patients who have symptoms that interfere with activities or athletics and for failure of nonsurgical management [9].
• Surgery for MDI is appropriate for patients with pain and instability that interferes with normal or sport-related activity that have failed extensive nonsurgical treatment [14].
• Surgical stabilization of posterior glenohumeral instability may be considered when recurrent involuntary posterior subluxation or dislocation occurs in spite of a concerted effort at a well-structured rehabilitation program [28].
• Operative interventions for atraumatic shoulder instability should be approached with caution, and only those with demonstrable pathology or intractable symptoms despite appropriate rehabilitation should be considered for surgical intervention [129].
• Surgical treatment of primary, traumatic, anterior shoulder instability results in reduced rates of recurrence compared with nonsurgical treatment at 10-year follow-up [82].
• First-time dislocators who underwent surgical stabilization had better outcomes than recurrent dislocators with regard to requiring additional surgery for recurrent dislocation (7% versus 32%) [86].
• 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 [26].
• 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 [26].
• Participation in a contact sport is not a contraindication to arthroscopic stabilization [26].
• 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 [26].
• 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%) [30].

Operative Management: Anterior Instability

• Arthroscopic Bankart repair has become common because it allows excellent visualization of the entire joint and is minimally invasive; it is now the treatment of choice among new surgeons in the United States [86].
• In a double-blind, randomized clinical trial evaluating arthroscopic Bankart repair versus sham surgery, patients with a first-time dislocation had decreased recurrence of instability and improved outcome scores after repair [86].
• A systematic review of level I and II studies demonstrated decreased recurrence of instability following arthroscopic Bankart repair when compared with physical therapy and sham surgery [86].
• Patients in the repair group for anterior instability were noted to have one-fifth the rate of recurrent instability and improved Western Ontario Shoulder Instability Index (WOSI) scores compared to controls [86].
• First-time dislocators had an average glenoid bone loss of 6.8% at the time of initial injury, supporting the role of early surgical intervention in high-risk populations [86].
• Radiographic evidence of dislocation arthropathy was reported in 41% of patients 8 years after arthroscopic Bankart repair [86].
• The presence of radiographic arthritis after arthroscopic Bankart repair did not correlate with outcome scores [86].
• Open Bankart repair requires transection or splitting of the subscapularis tendon, and mild losses in forward elevation and external rotation can occur, typically between 8° and 10° [86].
• In a series of 49 patients including 31 elite rugby players, 16% had recurrence of instability during the 26-year follow-up period after open Bankart repair [86].
• Of patients undergoing open Bankart repair, 65% had radiographic evidence of arthritis at final follow-up, most of which was considered mild, and 80% reported being pain free [86].
• Ninety-four percent of patients after open Bankart repair resumed athletic activity, with 75% of those at their original level of competition [86].
• In a randomized clinical trial comparing open versus arthroscopic Bankart repair, an increased rate of recurrence was noted after arthroscopic repair (23% versus 11% in open repair) [86].
• 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 [86].
• In a trial of isolated Bankart lesions randomized to arthroscopic versus open repair, improved Disability of the Arm, Shoulder and Hand scores were noted in the arthroscopic group, with no substantial difference in recurrence noted [86].
• A systematic review of more recent meta-analyses demonstrated no difference in recurrence between open and arthroscopic Bankart repair techniques [86].
• Most shoulder specialists consider arthroscopic anterior stabilization as the first-line treatment for recurrent glenohumeral instability [78].
• Patients with more than two or three instability episodes and/or significant capsular attenuation require capsular shifting in conjunction with Bankart repair to regain and maintain stability [78].
• Suture anchor techniques are biomechanically the strongest of eight repair techniques in a canine Bankart model [78].
• Early clinical outcomes of suture anchor repair realized similar results to open stabilization, even in high demand athletes, with redislocation rates of 6% and an 85% return to previous level of sporting activity [78].
• In a consecutive series of 85 patients with Bankart lesions treated arthroscopically with suture anchors, the overall recurrence rate was 10% over a mean follow-up period of 46 months [78].
• In the same series of 85 patients, 90% of cases had subjective outcome measures graded as good to excellent [78].
• Variables associated with successful outcomes in arthroscopic Bankart repair include use of a low anterior portal (5 o'clock position), repair of tear extension into the superior labrum, and placement of the suture anchors 2 mm in on the glenoid face articular cartilage [78].
• Advanced arthroscopic techniques include double-row labral repair, postero-inferior capsulolabral repair, and remplissage [78].
• Double-row fixation may better restore normal anatomy compared to single-row techniques [78].
• Advanced arthroscopic techniques may be indicated in the setting of small (<20%) bony Bankart lesions [78].
• Successful results were obtained in patients younger than 40 years with both primary and recurrent anterior shoulder instability after arthroscopic treatment [93].
• The success of treating anterior glenohumeral instability relies on multiple factors, including glenoid bone loss [84].
• Successful treatment of anterior instability of the shoulder requires a balance between restoring joint stability and minimizing loss of glenohumeral motion [98].
• 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 [74].

Operative Management: Posterior Instability

• Soft-tissue procedures for posterior instability include open or arthroscopic labral repair and posterior capsular shift [9].
• Some authors recommend plication of the rotator interval for posterior instability, though this is controversial [9].
• Options for posterior glenoid bone loss include distal tibial allograft or autograft reconstruction using posterior acromion, iliac crest, or distal clavicle [9].
• Recurrence is the most common complication of posterior instability surgery and is reported to be 8.5% in the general population [9].
• Recurrence rates for posterior instability are highest in overhead athletes [9].
• Recurrence rates increase with posterior glenoid bone loss >20%, which should be considered a contraindication to arthroscopic soft-tissue stabilization alone [9].
• Shoulder stiffness or adhesive capsulitis is a concern with rotator interval plication for posterior instability [9].
• In arthroscopic labral repair for posterior instability, a high lateral portal provides better access than a standard posterior portal [9].
• Primary arthroscopic treatment of posterior shoulder instability is associated with favorable outcomes and high return to sport and work rates [92].
• The early and midterm results of arthroscopic stabilization of the shoulder for posterior instability are promising [94].
• Treatment of posterior shoulder instability by capsulolabral reconstruction leads to good clinical outcomes; however the recurrence rate is high [81].
• 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 [25].
• Arthroscopic techniques for posterior instability repair have shown promising results, and results are generally more favorable than those after anterior instability repair [28].
• In a prospective cohort 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 and a majority at the same level of play [28].
• Several surgical approaches have been described for treating recurrent posterior glenohumeral instability, including the posterior deltoid-splitting approach [28].
• Shaffer et al. described a surgical approach to the posterior glenohumeral joint through an infraspinatus-splitting incision that offers safe and excellent exposure of the posterior capsule, labrum, and glenoid without requiring tendon detachment or causing neurologic compromise [28].
• Most surgeons prefer to split the deltoid at the posterior corner of the acromion and incise the infraspinatus tendon near its attachment to the greater tuberosity for open posterior repair [28].

Operative Management: Multidirectional Instability

• Arthroscopic pancapsular plication ± rotator interval closure is a surgical technique for MDI [14].
• If labral pathology is encountered during MDI surgery, anterior or posterior labral repair is indicated [14].
• To avoid asymmetric tightening in MDI surgery, capsulorrhaphy should address the inferior redundancy in a balanced fashion [14].
• Open anterior-inferior capsular shift is a surgical technique for MDI [14].
• Recurrence of MDI is 7% for both open and arthroscopic techniques [14].
• Axillary nerve injury is a complication of MDI surgery [14].
• Stiffness is a rare complication of MDI surgery [14].
• Subscapularis insufficiency is a complication after open MDI procedures [14].
• Arthroscopic and open capsular shifts have been successful in restoring stability and decreasing pain in MDI [26].
• Thermal capsulorrhaphy has recently shown a high complication rate for MDI [26].
• 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 [26].
• In patients with MDI where arthroscopic results are less predictable, an open capsular shift may provide a more predictable outcome [26].
• 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 [100].
• In managing shoulders with the AMBRI type of instability, the surgeon has the opportunity to use the redundant capsule to augment the labrum, creating a deeper stabilizing concavity [13].
• In managing shoulders with the AMBRI type of instability, rotator interval closure may be another useful adjunct [13].

Rehabilitation and Post-Operative Care

• Postoperatively for posterior instability, the shoulder should be placed in a rigid immobilizer with the arm abducted to 30° in neutral rotation [9].
• After a short period of immobilization for posterior instability, ROM exercises may begin [9].
• Strengthening for posterior instability should begin at 12 weeks [9].
• Patients may return to heavy labor or contact sports 6 months after posterior instability surgery [9].
• The pooled published rate of return to any sport after posterior instability surgery is 91% [9].
• The pooled published rate of return to preinjury level of sport after posterior instability surgery is 67% [9].
• For anterior instability, postoperatively the shoulder was placed in a sling for 3 weeks, while allowing nonresisted activities of daily living without elevation of the shoulder [128].
• Patients immediately began physiotherapy after anterior instability surgery, which continuously increased in intensity over the next 9 weeks [128].
• Return to contact in training after anterior instability surgery was allowed after 12 weeks [128].
• Return to full contact and competition after anterior instability surgery usually follows within the next 3 months, depending on progress of physiotherapy [128].
• For anterior instability in patients older than 40 years, postoperatively the shoulder was placed in a sling for 3 weeks, while allowing nonresisted activities of daily living without elevation of the shoulder [135].
• Patients immediately began physiotherapy after anterior instability surgery in patients older than 40 years, which continuously increased in intensity over the next 9 weeks [135].
• Return to training after anterior instability surgery in patients older than 40 years was generally allowed after 12 weeks [135].
• Return to full contact training and competition after anterior instability surgery in patients older than 40 years followed within the next 3 months, depending on the progress of physiotherapy [135].
• For radiofrequency capsular shrinkage for voluntary shoulder instability, the arm was placed in a sling for comfort for a few days [130].
• Motion was allowed after radiofrequency capsular shrinkage, avoiding extremes in all directions for the first 6 weeks [130].
• Proprioceptive physiotherapy was initiated within the first week after radiofrequency capsular shrinkage [130].
• Athletes may return to play after a shoulder dislocation or after stabilization surgery when strength and mobility have normalized [26].

Surgical Techniques and Complications

• Recent randomized trials and systematic reviews have not shown the superiority of modern arthroscopic techniques compared with open repairs for shoulder instability [13].
• Open repair resulted in a significantly lower risk of recurrence compared to arthroscopic repair in younger male patients with a Hill-Sachs lesion [13].
• Arthroscopic and open repair techniques for the treatment of recurrent traumatic shoulder instability yield comparable results if the procedure is selected on the basis of the pathologic findings at the time of surgery [13].
• The available evidence indicates that arthroscopic approaches are not as effective as open approaches in preventing recurrent instability or enabling patients to return to work [13].
• It is not uncommon to see shoulders in which suture anchors were

Complications

Recurrence and Failure of Stabilization

• With a follow-up of 97%, about one third of the stabilized shoulders experienced at least one redislocation after 8 to 10 years [31].
• 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 [133].
• 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 [42].
• The 1-year outcomes in this prospective study suggest superiority of operative over non-operative treatment for posterior shoulder instability [8].

Arthropathy and Cartilage Damage

• The natural history of the first time shoulder dislocations is bound up with arthropathy [37].
• Osteochondral lesions of the humeral head were noted in 34 patients and chondral lesions were noted in an additional 23 out of 63 patients with first-time traumatic dislocations evaluated arthroscopically within 10 days [43].
• In a series of 24 patients with first-time anterior shoulder dislocation assessed arthroscopically 1 to 3 days after injury, osteochondral lesions were found in six shoulders and chondral lesions were noted in the remaining 18 [43].
• Of 88 patients with acute instability (within 90 days of index injury to surgery), 24% had grade I or higher chondral lesions and 12% had Grade III or IV chondral damage [43].
• The incidence of shoulder arthropathy in patients with shoulder instability is difficult to measure due to the long time period between dislocation and arthritis and the high rate of recurrence ranging from 10% to 90% after an initial dislocation [43].

Surgical Complications: Arthroscopic and Open

• Misplaced suture anchors can give rise to secondary degenerative joint disease or "anchor arthropathy" [13].
• Use of intra-articular infusion of local antibiotics via a pain pump after arthroscopic instability repairs results in a risk of glenohumeral chondrolysis [13].
• The open Latarjet procedure is a safe and reliable technique for recurrent anterior shoulder instability, as demonstrated by long-term follow-up studies [39, 40].
• 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 [110].
• Routine use of bone transfers for glenohumeral instability in the absence of major glenoid bone loss is not advisable because of the increased risk of arthritis, screw-related problems, damage to the subscapularis, and difficulty in revision [13].
• Arthroscopic approaches are not as effective as open approaches in preventing recurrent instability or enabling patients to return to work [13].
• Open repair resulted in a significantly lower risk of recurrence compared to arthroscopic repair, particularly in younger male patients with a Hill-Sachs lesion [13].
• Nerve injuries from interscalene blocks can be permanent [13].

Complications in Arthroplasty Patients with Instability History

• 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 [141].
• 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 [141].
• Approximately 80% of instability complications after total shoulder arthroplasty involve anterior or superior instability, and most are the result of soft-tissue deficiency [141].
• Anterior instability after total shoulder arthroplasty is most commonly associated with subscapularis failure, glenoid component malposition, or anterior deltoid dysfunction [141].
• Posterior instability after total shoulder arthroplasty has been attributed most often to malposition of the components, including excessive component retroversion and soft-tissue imbalance [141].
• Inferior instability after shoulder arthroplasty is related to the loss of normal humeral height and is most common after hemiarthroplasty for proximal humeral fractures [141].
• 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 [36].
• Component loosening occurred in 6.31% of all shoulders and instability in 4.9% of all shoulders in a report of complications after unconstrained total shoulder arthroplasties [127].
• Periprosthetic fracture occurred in 1.8% of all shoulders and rotator cuff tear in 1.3% of all shoulders in a report of complications after unconstrained total shoulder arthroplasties [127].

Graft and Reconstruction Complications

• Short-term outcomes for pre-shaped allograft for glenoid reconstruction are reassuring, but more research is needed to study long-term graft union, graft resorption, glenohumeral arthritis, and patient outcomes including recurrent shoulder instability [32].

Recovery

Non-Operative Management

• The optimal nonoperative treatment of a shoulder dislocation is still unknown and deserves further study [26].
• Nonsurgical management is considered in preadolescents, older patients (older than 30 years), and/or in those with low activity demands, as well as in-season athletes [45].
• Adequate nonsurgical treatment typically involves a brief period of sling immobilization (3 to 7 days), followed by a course of structured rehabilitation focusing on cryotherapy, restoration of full range of motion, periscapular and rotator cuff strengthening to improve dynamic stabilizers, and finally stabilization and sport-specific drills [45].
• Multiple episodes of instability have been linked to increased attritional glenoid bone loss [45].
• Multiple episodes of instability have been linked to increased procedural complexity such as remplissage or coracoid transfer [45].
• Multiple episodes of instability have been linked to increased severity of glenoid chondral defects [45].
• Multiple episodes of instability have been linked to compromised outcomes at the time of surgical shoulder stabilization [45].
• Multiple episodes of instability have been linked to higher rates of glenohumeral osteoarthritis [45].

Operative Management

• With a follow-up of 97%, about one third of the stabilized shoulders experienced at least one redislocation after 8 to 10 years following arthroscopic shoulder stabilization using suture anchors [31].
• The open Latarjet procedure is a safe and reliable technique for recurrent anterior shoulder instability [39].
• The outcomes at 3 years' follow-up for revision of failed Latarjet with the Eden-Hybinette surgical technique were satisfactory in 80% of patients [108].
• 86% of patients had stable shoulders at 3 years' follow-up for revision of failed Latarjet with the Eden-Hybinette surgical technique [108].
• The number of episodes of dislocation before surgery and the delayed surgical intervention did not increase the recurrent anterior shoulder instability rates postoperatively following an open Latarjet-Bristow procedure [160].

Return to Sport

• 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 [161].

Key Evidence

• [L4] The MOON Shoulder Instability Study has enrolled the largest cohort of patients undergoing shoulder stabilization to date. [1] (10.1177/0363546518755752)
• [L5] The authors propose a classification system, which challenges previous systems by being all inclusive and recognises that more than one pathology can occur in an individual shoulder. [3] (10.1016/j.cuor.2004.04.002)
• [L5] [4] (10.1177/17585732251320070)
• [L3] Long-term follow-up demonstrates that nearly 40% of patients treated non-operatively for posterior shoulder instability eventually require surgery. [5] (10.1177/2325967118s00098)
• [L4] At long-term follow-up of 17 years, a high rate of poor outcomes was observed following nonoperative management of anterior shoulder instability. [6] (10.1016/j.jse.2021.07.016)
• [L5] Proper evaluation of bone loss best determines shoulder instability surgical indications and outcomes. [7] (10.1016/j.arthro.2021.01.004)
• [L3] The 1-year outcomes in this prospective study suggest superiority of operative over non-operative treatment for posterior shoulder instability. [8] (10.1016/j.otsr.2017.08.004)
• [L4] Many different diagnostic examinations for assessing shoulder instability are used and a high variety is seen in the use of diagnostic tools. [11] (10.1007/s00402-016-2443-7)
• [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)
• [L5] Recurrent posterior shoulder instability is an uncommon condition often unrecognized, leading to incorrect diagnoses and delays. [15] (10.5435/00124635-200608000-00004)
• [L3] Identification of these critical radiographic variables on magnetic resonance arthrography assists in the accurate diagnosis and management of clinically significant posterior shoulder instability. [18] (10.1177/0363546516660076)
• [L4] They are considered safe and clinically effective for the management of anterior shoulder instability with glenoid bone loss. [21] (10.5435/jaaos-d-22-00837)
• [L4] Posterior shoulder dislocation is a rare and challenging injury with varied mechanisms of trauma that complicate diagnosis. [22] (10.5435/jaaos-22-03-145)
• [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. [24] (10.1177/2325967115607434)
• [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. [25] (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%). [30] (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. [31] (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. [32] (10.1016/j.eats.2017.10.007)
• [L2] We recommend using it in following up patients with shoulder instability. [33] (10.1016/j.otsr.2016.10.024)
• [L5] [34] (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. [36] (10.1016/j.jse.2023.07.005)
• [Abstract] The natural history of the first time shoulder dislocations is bound up with arthropathy. [37] (10.1016/j.jse.2007.02.100)
• [L3] This long-term follow-up study demonstrated that the open Latarjet procedure is a safe and reliable technique for recurrent anterior shoulder instability. [39] (10.1016/j.jse.2021.03.097)
• [L3] This long-term follow-up study demonstrated that the open Latarjet procedure is a safe and reliable technique for recurrent anterior shoulder instability. [40] (10.1007/s00402-020-03426-2)
• [L3] Regardless of the radiologist interpretation of MRA, patients with symptomatic posterior shoulder instability do benefit from arthroscopic stabilization surgery. [41] (10.1016/j.xrrt.2026.100675)
• [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. [42] (10.1016/j.asmr.2023.03.014)
• [L4] [43] (10.1016/j.csm.2004.08.010)
• [L5] [44] (10.1016/j.arthro.2024.04.035)
• [L3] Most patients younger than 40 years with shoulder instability who were initially treated nonoperatively for 6 months were definitively treated without surgery. [46] (10.1016/j.arthro.2021.03.047)
• [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. [58] (10.1177/2325967115584318)
• [L3] [60] (10.1016/j.jse.2024.01.043)
• [L5] The system categorizes instability based on frequency, aetiology, direction, and severity. [63] (10.1136/bjsm.2009.071183)
• [L2] [65] (10.1002/ksa.70336)
• [L2] Primary non-operative management is a prominent risk factor for recurrence of shoulder instability. [66] (10.1136/bjsports-2016-096895)
• [L3] Minor shoulder instability is an intra-articular pathology presenting with extra-articular subacromial impingement symptoms. [69] (10.1007/s00167-011-1552-7)
• [L1] Shoulder instability cannot reliably be classified using the ICD-9 coding system. [71] (10.1016/j.jse.2008.10.005)
• [L3] Microinstability is diagnostically challenging and can be diagnosed in young patients with ambiguous shoulder pain during motion, without instability. [72] (10.1007/s00167-022-06941-4)
• [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. [74] (10.1016/j.jse.2017.10.032)
• [Paper] Treatment of posterior shoulder instability by capsulolabral reconstruction leads to good clinical outcomes; however the recurrence rate is high. [81] (10.1016/j.otsr.2017.08.002)
• [L1] Surgical treatment of primary, traumatic, anterior shoulder instability results in reduced rates of recurrence compared with nonsurgical treatment at 10-year follow-up. [82] (10.1016/j.arthro.2006.11.026)
• [L5] The success of treating anterior glenohumeral instability relies on multiple factors, including glenoid bone loss. [84] (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. [92] (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. [93] (10.1016/j.jse.2023.05.029)
• [L1] The early and midterm results of arthroscopic stabilization of the shoulder for posterior instability are promising. [94] (10.1016/j.arthro.2014.11.009)
• [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. [95] (10.1007/s11678-017-0404-6)
• [L5] Successful treatment of anterior instability of the shoulder requires a balance between restoring joint stability and minimizing loss of glenohumeral motion. [98] (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. [100] (10.1177/2325967121s00021)
• [L5] The shoulder depends on dynamic and static stabilizers because it has little inherent stability, making it prone to instability. [103] (10.1016/j.ocl.2019.11.008)
• [L4] The outcomes at 3 years' follow-up were satisfactory in 80% of patients and 86% had stable shoulders. [108] (10.1016/j.otsr.2019.12.009)
• [L3] Nonoperative treatment of shoulder instability has substantial societal costs. [109] (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. [110] (10.1177/03635465211042314)
• [L4] Recent studies continue to demonstrate a role for nonoperative treatment in the successful long-term management of anterior glenohumeral instability. [117] (10.1007/s12178-017-9432-5)
• [L4] NHL team physicians strongly favor nonoperative management in-season for initial posterior instability events of the shoulder. [119] (10.1177/23259671261440208)
• [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. [120] (10.1016/j.arthro.2024.07.039)
• [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. [121] (10.1177/03635465231162271)
• [L5] Magnetic resonance arthrography is regarded as the gold-standard imaging modality for shoulder instability. [123] (10.1016/j.mric.2019.12.005)
• [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. [125] (10.1016/j.csm.2014.06.006)
• [L4] [128] (10.1016/j.jse.2019.12.012)
• [L5] [129] (10.1177/1758573218815002)
• [L4] [130] (10.1016/j.jse.2005.11.011)
• [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. [131] (10.1007/s00402-012-1656-7)
• [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. [133] (10.1177/0363546519886861)
• [L4] [135] (10.1016/j.jse.2024.09.022)
• [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. [136] (10.1016/j.jseint.2024.03.012)
• [L5] MR-arthrography is identified as the main tool in diagnosing shoulder instability injuries. [139] (10.21037/qims.2017.08.05)
• [L3] [145] (10.1097/corr.0000000000002320)
• [L4] In the future, we expect CT to be superseded by MRI in anterior shoulder instability. [146] (10.1016/j.jseint.2025.101440)
• [L4] [150] (10.1016/j.jisako.2025.100765)
• [L4] Radiography can be used for screening patients for significant glenoid bone loss. [152] (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. [153] (10.3109/02841850903524421)
• [L3] ZTE MRI demonstrated high reproducibility for the evaluation of glenoid bone defect in shoulders with anterior instability. [156] (10.1016/j.jseint.2024.03.003)
• [L4] Additionally, MRI is a valid imaging tool to diagnose and measure osseous lesions of the shoulder. [157] (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. [158] (10.2106/00004623-198264040-00005)
• [L4] The number of episodes of dislocation before surgery and the delayed surgical intervention did not increase the recurrent anterior shoulder instability rates postoperatively. [160] (10.1016/j.jseint.2022.12.003)
• [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. [161] (10.1177/2325967121s00549)

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[146] MRI augmented with novel artificial intelligence system is superior to CT in shoulder instability. JSES International. 2026. DOI: 10.1016/j.jseint.2025.101440

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[152] Imaging methods for quantifying glenoid and Hill-Sachs bone loss in traumatic instability of the shoulder: a scoping review. BMC Musculoskeletal Disorders. 2015. DOI: 10.1186/s12891-015-0607-1

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