50.1 Goals of Procedure

The goals of reverse shoulder arthroplasty (RSA) are to restore function and minimize pain related to arthritic change of the glenohumeral joint. While originally found to be most advantageous for shoulders with deficient rotator cuffs, the procedure’s indications and use have expanded dramatically in the past decade. An additional goal of the procedure is to provide a stable joint that can restore function with a reasonable degree of longevity.

50.2 Advantages

There are several advantages to using reverse shoulder prosthesis. The most widely accepted advantage is restoration of the ability to raise the arm in those with a massive, irreparable rotator cuff tear and chronic loss of elevation. This procedure has demonstrated promising results in those with rotator cuff-tear arthropathy (CTA), as well as in those with irreparable rotator cuffs and little or no glenohumeral arthritis. Another advantage is that because the glenoid component relies on secure screw fixation to the scapula, this prosthesis can be used in the setting of altered glenoid anatomy, such as in patients with glenoid version abnormalities or bone loss. As such, it is also ideal for revision shoulder arthroplasty, such as in cases of failed anatomic shoulder implants in which the glenoid bone stock has been eroded. A third advantage of the RSA is its versatility as an excellent option for proximal humerus fractures. Recent data have demonstrated promising outcomes when a reverse implant is used to treat unfixable acute proximal humerus fractures as well as proximal humeral nonunions. Anatomic shoulder implants and hemiarthroplasties function poorly when the tuberosities fail to heal, and as the reverse implant is not reliant on healed tuberosities or a functional rotator cuff, the reverse has demonstrated superior results in these clinical scenarios. With similar consideration, the reverse implant can be used in patients with intact but degenerated rotator cuffs, in whom an anatomic replacement may function well temporarily but will eventually fail as the rotator cuff quality deteriorates.

50.3 Indications

The original and most commonly applied indication for RSA remains for CTA with glenohumeral arthritis. The indications are expanding, and though there are many favorable studies that incorporate heterogeneous indications, the outcomes for this indication have demonstrated reliable results. ^{1 – 4} As discussed earlier, the reverse prosthesis has also been reported to be used successfully in patients with an intact rotator cuff, particularly those with glenoid version abnormalities or bone loss, those with proximal humeral malunions, or those with at-risk rotator cuffs including those with degenerated or thin cuffs and those with inflammatory arthropathy (i.e., rheumatoid arthritis). An additional indication for this implant is for complex or comminuted proximal humerus fractures that are unfixable or in which the tuberosities would be at risk for non-healing if a hemiarthroplasty were to be used, as the outcomes of hemiarthroplasties are dependent on tuberosity healing. The reverse prosthesis can also be used to treat patients with preoperative deltoid impairment, and while there is some improvement in pain and function, the results remain inferior to those with unimpaired deltoid muscles. The RSA has also been used successfully in managing patients with significant proximal humeral bone loss, and in those cases of failed hemiarthroplasty.

50.4 Contraindications

One of the primary contraindications to the RSA is the absence of a functional deltoid muscle, secondary to any cause (i.e., permanent axillary nerve dysfunction, failure to heal following prior surgery). Another contraindication would be any limitation of mental capacity, such as severe dementia, that would preclude appropriate adherence to postoperative restrictions. Patients who are unable to comply with the critical portions of the postoperative protocol are at high risk of complications. An additional general contraindication to any sort of arthroplasty would be the presence of medical comorbidities that might place the patient’s life at risk should he or she undergo anesthesia.

The presence of a local or systemic infection precludes the implantation of an RSA, and the infection should be confirmed to be eradicated prior to placement of any prosthesis. Finally, inadequate glenoid bone stock precludes placement of the glenosphere portion of the RSA, and in these cases, we would typically utilize a hemiarthroplasty.

50.5 Preoperative Preparation/Positioning

Preoperative preparation begins with a thorough history and physical examination of the patient. Particular attention is given toward portions of the history that might elucidate whether one of the above-mentioned contraindications is present, as well as if the patient is taking any medications that may affect surgery such as anticoagulants or disease-modifying antirheumatic drugs (DMARDs) in rheumatoid patients. Standard radiographs of the shoulder are obtained, with the two most useful views being the anteroposterior (AP) view in external rotation and the axillary view. Though CT scan is obtained as well, we find that the axillary radiograph provides a more general picture of humeral head subluxation relative to the glenoid. The gravity-assisted (i.e., standing) AP radiograph is useful to appreciate the superior migration that is typical of patients with CTA, as well as to obtain a general sense of medialization of the center of rotation (COR).

The CT scan is critical for preoperative planning, and we routinely obtain this on almost every patient, unless the patient is unable to undergo this imaging study. We utilize the Walch classification ⁵ to evaluate the glenoid morphology. On an axial view that is representative of the center of the glenoid, Friedman’s line ⁶ is used to evaluate the glenoid version. The coronal views are used to assess glenoid inclination.

The patient is secured comfortably in the beach-chair position, with the backrest inclined to roughly 60 degrees. The torso is angled roughly 20 to 30 degrees off the backrest to ensure that the entire scapula is free. This modified lateralized position allows for adduction and extension of the humerus. Great care is taken during this portion to ensure that the head and neck are safely positioned without tension on the brachial plexus. The knees are bent slightly, and all bony prominences are well padded. We do not use a pneumatic arm holder, but rather a well-padded Mayo stand. The entire upper extremity is draped freely and prepared in a sterile manner.