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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.

Anatomy & Pathophysiology

Glenoid and Scapular Anatomy

• The glenoid is suspended from the body of the scapula by the neck and fixed to the clavicle by the acromioclavicular and coracoclavicular ligaments [3].
• As the face of the glenoid transitions into the neck, the glenoid vault narrows [3].
• The scapular spine is subcutaneous posteriorly and widens gradually as it transitions into the base of the acromion laterally [3].
• The acromion curves anteriorly and meets the clavicle at the acromioclavicular joint and the coracoid via the coracoacromial ligament, which originates under the anterior margin of the acromion [3].
• The suprascapular nerve arises from the C4–C5 nerve roots off of the supraclavicular brachial plexus at “Erb’s point” [3].
• The suprascapular nerve runs just medial to the base of the coracoid, under the transverse scapular ligament within the suprascapular notch, and gives off branches to the supraspinatus within 1 cm of the notch [3].
• The suprascapular nerve continues through the supraspinatus fossa heading laterally and distally on the under surface of the supraspinatus [3].
• The suprascapular nerve runs under the ill-defined spinoglenoid ligament around the lateral base of the scapula within spinoglenoid notch before terminating in posterior capsular sensory branches heading laterally and an infraspinatus motor branch heading medially within 1 cm of the lateral margin of the scapular spine [3].
• Cadaver studies show the suprascapular nerve is present 29 mm (23 to 35 mm) from the superior rim of the glenoid at the suprascapular notch [3].
• Cadaver studies show the suprascapular nerve is present 18 mm (14 to 24 mm) from the posterior rim at the spinoglenoid notch [3].
• Injury to the suprascapular nerve can cause pain and denervation of the supraspinatus and infraspinatus [3].

Biomechanics and Pathophysiology

• Anatomic total shoulder arthroplasties and hemiarthroplasties are dependent on the rotator cuff to center the head in the glenoid and to optimize larger periscapular muscle function [7].
• In the absence of a functional rotator cuff, the deltoid pulls the humerus proximally, shearing along the glenoid and resulting in eccentric glenoid wear, acetabularization of the acromion, and pseudoparalysis [7].
• The reverse shoulder arthroplasty does not require the rotator cuff for function but is dependent on an intact deltoid neuromuscular unit [7].
• The semiconstrained nature of the reverse prosthesis provides a stable fulcrum that allows the deltoid to elevate the shoulder even in the absence of a functional rotator cuff [4].
• In the Grammont reverse prosthesis, the center of rotation is medial to the glenoid component–bone interface to decrease shear stress and provide compressive stress, aiming to decrease the chances of glenoid loosening [4].
• The humeral component in the Grammont design is inset, resting almost completely inside the proximal humerus metaphysis [4].
• The opening angle of the polyethylene in the Grammont design is relatively horizontal at 155 degrees compared with conventional arthroplasty [4].
• Once articulated, the humerus is more medial and more distal than preoperatively, providing a mechanical advantage to the deltoid for active elevation in the absence of a rotator cuff [4].
• The traditional Grammont style decreases shear forces seen by the glenoid and lowers baseplate failure by medializing the center of rotation, but this is associated with the risk of inferior scapular notching in adduction [7].
• Distalization doubles the lever arm of the deltoid and optimizes the length–tension curve of its sarcomeres, increasing its efficiency by 30% at the cost of rotational strength [7].
• Lateralized glenosphere and lateralized humerus designs have gained popularity to improve the rotational profile, deltoid function, implant stability, and decrease impingement such as scapular notching [7].
• Early reverse designs had a high failure rate due to the profound lever arm on the glenoid and baseplate bone [7].
• Recent reverse designs have a better track record but increased forces are seen by the scapula and acromion [7].

Periprosthetic Scapular Fracture Pathophysiology

• Periprosthetic scapular fractures are universally associated with stable glenoid implants [2].
• Fracture is unlikely in the face of dislocation, glenosphere dissociation, or baseplate pullout at the bone–baseplate interface [2].
• Periprosthetic scapular fracture has been noted to result in new glenohumeral instability due to the change of the orientation of the glenosphere and loss of deltoid tension [2].
• Postoperative periprosthetic scapular fracture is a challenge unique to reverse shoulder arthroplasty and occurs more commonly than humeral fractures [7].
• Postoperative periprosthetic scapular fractures are an effect of nonphysiologic forces transferred from the implant to the scapula, often in a suboptimal host [7].
• Fatigue fracture has been found to occur through already weakened acromiums or those with preexisting lesions [7].
• Acromial thinning and eventual fragmentation occur at the final stages of rotator cuff-tear arthropathy as the humeral head acetabularizes [7].

Clinical Presentation

Periprosthetic Scapular Fractures

• The weak point in periprosthetic scapular fracture injuries is the scapular bone [2].
• Periprosthetic scapular fractures are unlikely in the presence of dislocation, glenosphere dissociation, or baseplate pullout at the bone–baseplate interface [2].
• Periprosthetic scapular fractures have been noted to rarely result in new glenohumeral instability [2].
• New glenohumeral instability following periprosthetic scapular fracture is due to a change in the orientation of the glenosphere and loss of deltoid tension [2].
• Diagnosis of periprosthetic fractures is often subtle and requires a high index of suspicion [2].
• Workup for periprosthetic fractures should begin with a complete history and examination [2].
• Past medical history should elucidate the underlying diagnosis for the index surgery and subsequent surgeries [2].
• Complications including infection should be accounted for in the past medical history [2].
• The examiner should understand the patient's shoulder function and level of disability before surgery, after surgery, and at present [2].
• The examiner should understand the time course of changes in shoulder function and disability [2].
• In the case of a stress reaction, new pain at the base of the acromion may be the only finding [2].
• New pain at the base of the acromion in a stress reaction should raise suspicion and spark further imaging or a period of rest [2].
• Stress fractures can be more painful than after they propagate into a displaced fracture [2].
• Patients typically present around their 8th decade of life after a sudden increase in pain or loss of function [2].
• Patients typically present after a sudden increase in pain or loss of function in an otherwise smooth postoperative course [2].
• Presentation for periprosthetic scapular fracture is generally within 1 year but up to 2 years from surgery [2].
• Patients who go on to have periprosthetic scapular fractures initially outperform those who do not [2].
• Past medical history must identify risk factors including a history of steroid use, osteoporosis, subacromial decompression, or rotator cuff tear arthropathy [2].
• Previous operative reports, clinic notes, and imaging can help provide a thorough understanding of any previous surgeries on the shoulder or history of radiation [2].
• Physical examination starts with inspection [2].
• Deformity is concerning for dislocation, hematoma, or displaced fracture [2].
• Erythema or incisional dehiscence is concerning for infection [2].
• Tenderness along the acromion or scapular spine raises suspicion for fracture which should be confirmed with imaging [2].
• A complete neurovascular examination is performed as part of the physical examination [2].
• Assessment of active and passive motion is performed as part of the physical examination [2].
• Fracture can result in motion limited by pain, new weakness, or loss of function [2].
• Infection should be investigated with laboratory tests [2].
• A sudden loss of function or increase in pain is consistent with both scapular fracture and infection [2].
• A sudden loss of function or increase in pain should trigger further workup [2].

Investigations

Periprosthetic Scapular Fracture Diagnosis and Workup

• Diagnosis of periprosthetic scapular fractures is often subtle and requires a high index of suspicion [2].
• The workup for periprosthetic scapular fractures should begin with a complete history and examination [2].
• The examiner should understand the patient's shoulder function and level of disability before surgery, after surgery, and at present, as well as the time course of these changes [2].
• New pain at the base of the acromion may be the only finding in a stress reaction and should raise suspicion for further imaging or a period of rest [2].
• Patients with periprosthetic scapular fractures typically present around their 8th decade of life after a sudden increase in pain or loss of function in an otherwise smooth postoperative course [2].
• Periprosthetic scapular fractures generally occur within 1 year but up to 2 years from surgery [2].
• Inspection for deformity is concerning for dislocation, hematoma, or displaced fracture [2].
• A complete neurovascular examination is performed as well as assessment of active and passive motion [2].
• A sudden loss of function or increase in pain is consistent with both scapular fracture and infection and should trigger further workup [2].

Preoperative Imaging and Planning

• Careful assessment of the preoperative radiographs and CT with three-dimensional reconstruction is extremely useful in preparation for surgery [5].
• The main goals of preoperative imaging include understanding the fracture pattern and anticipating the ideal height of stem implantation [5].
• Radiographs of both humeri (affected and unaffected) with magnifier markers may be used to understand where the stem should be positioned in reference to the fracture line on the humeral shaft [5].
• The glenoid should be assessed in radiographs and CT to plan for component positioning, version, inclination, and rotation, as well as anticipated screw length [5].
• Associated fractures of the rim of the glenoid in anterior or posterior fracture-dislocations are rare [5].
• Most of the times, the size of the fractured glenoid rim is small enough not to interfere with secure baseplate placement [5].
• If the size of the fractured glenoid rim is large enough to interfere with the stability of the glenoid baseplate, fixation with small fragment screws may be performed [5].
• The glenoid should be assessed on CT for glenoid component implantation [5].
• Most surgeons do not use fluoroscopy for this procedure [5].

Treatment

Indications and Rationale

• Reverse shoulder arthroplasty is the replacement procedure of choice when arthroplasty is considered for proximal humeral fractures [4].
• Tuberosity and rotator cuff-related complications are the main reason for poor functional outcome when a humeral head replacement is implanted for management of a proximal humeral fracture [4].
• Shoulder arthroplasty is considered for proximal humeral nonunion in the presence of severe cavitation and bone loss at the humeral head and metaphysis or collapse and degenerative change of the humeral articular surface [6].
• Severe tuberosity malunion in the setting of a proximal humeral nonunion is more reliably compensated for with reverse arthroplasty than with osteotomy and internal fixation [6].
• Reverse shoulder arthroplasty may improve shoulder function in patients with nonunions associated with severe tuberosity malunions [6].

Prosthesis Design and Biomechanics

• The Grammont reverse prosthesis features an articulating glenoid component shaped as a third of a sphere [4].
• In the Grammont design, the center of rotation is medial to the glenoid component–bone interface to decrease shear stress and provide compressive stress, aiming to decrease the chances of glenoid loosening [4].
• The opening angle of the polyethylene in the Grammont design is 155 degrees [4].
• Articulation of the Grammont implants results in the humerus being more medial and more distal than preoperatively, providing a mechanical advantage to the deltoid for active elevation [4].
• The 155-degree opening angle in the Grammont design was selected to decrease the chances of dislocation [4].
• The humeral component in the Grammont design was recommended to be implanted in more anteversion (0 to 10 degrees of retroversion) than conventional arthroplasty [4].
• Subsequent reverse designs with a larger portion of a sphere place the center of rotation more lateral than the Grammont prosthesis [4].
• Subsequent reverse designs with a larger portion of a sphere utilize an opening angle of 135 degrees for the humeral component [4].
• Later reverse designs introduced onlay humeral bearings that lateralize the position of the humerus without changing the center of rotation [4].
• Later reverse designs with onlay humeral bearings utilize a 145-degree opening angle for the bearing [4].
• There is very little published on reverse arthroplasty biomechanics in the setting of a proximal humeral fracture [4].

Surgical Technique and Tuberosity Management

• Some surgeons initially elected to implant a reverse arthroplasty in proximal humeral fractures without repair, or sometimes with excision, of the greater tuberosity and/or lesser tuberosity [4].
• Healing of at least the greater tuberosity in good position provides a higher chance of restoration of active external rotation [4].
• Not performing a tuberosity repair at the time of reverse arthroplasty for proximal humeral nonunion has been correlated with a higher rate of dislocation [4].
• Technical principles for reverse arthroplasty in fracture may need to be modified to enhance tuberosity healing by avoiding translating the humeral shaft too lateral or too distal, allowing the tuberosities to overlap a few millimeters with the shaft [4].
• Use of a stem with fracture-dedicated features, such as a proximal ingrowth surface, small cross section, and holes for suture fixation, may be beneficial [4].

Comparison with Hemiarthroplasty

• Hemiarthroplasty is less commonly considered than reverse arthroplasty for proximal humeral nonunion [6].
• The functional outcome of hemiarthroplasty for nonunion is particularly concerning when tuberosity osteotomies need to be added [6].
• Studies reporting on hemiarthroplasty for nonunion suggest the procedure may be effective in reducing or eliminating pain but is associated with a high rate of complications that often require further surgery and disappointing functional recovery [6].

Complications

• Scapular notching is a complication of reverse shoulder arthroplasty [1].
• The clinical impact of scapular notching on outcomes after reverse total shoulder arthroplasty has been analyzed in a study of 476 shoulders [1].
• Humeral version in reverse shoulder arthroplasty affects impingement during activities of daily living [1].
• Subscapularis tendon integrity impacts shoulder function after reverse shoulder arthroplasty [1].
• Component positioning affects the intrinsic stability of the reverse shoulder arthroplasty [1].
• Humeral component lateralization in reverse shoulder arthroplasty affects rotator cuff torque [1].

References

[1] Campbell S Operative Orthopaedics 4 Volume Set. RECONSTRUCTIVE PROCEDURES OF THE SHOULDER AND ELBOW IN ADULTS > REVERSE SHOULDER ARTHROPLASTY.

[2] Rockwood And Green S Fractures In Adults. 29: Principles of Nonunion and Bone Defect Treatment > Injuries Associated with Periprosthetic Scapular Fractures About Reverse Shoulder Arthroplasty.

[3] Rockwood And Green S Fractures In Adults. 29: Principles of Nonunion and Bone Defect Treatment > Pathoanatomy and Applied Anatomy Related to Periprosthetic Scapular Fractures About Reverse Shoulder Arthroplasty.

[4] Rockwood And Green S Fractures In Adults. 29: Principles of Nonunion and Bone Defect Treatment > Reverse Shoulder Arthroplasty.

[5] Rockwood And Green S Fractures In Adults. 29: Principles of Nonunion and Bone Defect Treatment > Preoperative Planning > Reverse Shoulder Arthroplasty for Fracture: Preoperative Planning Checklist.

[6] Rockwood And Green S Fractures In Adults. 29: Principles of Nonunion and Bone Defect Treatment > Reverse Shoulder Arthroplasty and Hemiarthroplasty.

[7] Rockwood And Green S Fractures In Adults. 29: Principles of Nonunion and Bone Defect Treatment > Periprosthetic Scapular Fractures About Reverse Shoulder Arthroplasty.