Arthroplasty of the GH joint falls into several categories, the most common of which are total shoulder replacement arthroplasty, in which the glenoid and humeral surfaces are replaced and hemireplacement arthroplasty (hemiarthroplasty), in which one surface, the humeral head, is replaced. Other categories of shoulder arthroplasty include interpositional and resurfacing arthroplasties, which involve less extensive removal of bone.

Indications for Surgery
The following impairments associated with these pathologies are widely accepted indications for GH arthroplasty.
• The primary indication is persistent and incapacitating pain (at rest or with activity) secondary to GH joint destruction.

• Secondary indications include loss of shoulder mobility or stability and upper extremity strength leading to inability to perform functional tasks with the involved upper extremity.

Procedures
Background
Implant design, materials, and fixation. Since the pioneering work of Neer during the 1960s and 1970s and many other investigators, prosthetic designs and surgical techniques for replacing the shoulder joint have continued to evolve. The designs of current-day total shoulder replacement (TSR), composed of a high-density polyethylene glenoid component (usually all plastic) and a modular humeral component made of an inert metal, closely approximate the biomechanical characteristics of the human shoulder.
Fixation of the prosthetic components is achieved with a press fit, bio-ingrowth, or cement. The type of fixation selected by the surgeon depends on the component (glenoid or humeral), the underlying pathology, and the quality of the bone stock. Cement fixation is most often necessary in patients with osteoporosis.

Selection of procedure. Controversy exists over the specific criteria for selection of TSR versus hemiarthroplasty, but in general it depends on the etiology and severity of the joint deterioration and the condition of the periarticular soft tissues, particularly the rotator cuff mechanism. Several examples that follow underscore the complexity of the clinical decision-making process involved in the choice of operative procedure and prosthetic design.

In patients with late-stage primary OA, the most common pathology associated with shoulder arthroplasty, the GH joint typically exhibits loss or thinning or the articular cartilage of the head of the humerus and the posterior portion of the glenoid fossa. In addition, the rotator cuff is intact in approximately 90% to 95% of these patients, making them good candidates for either TSR or hemiarthroplasty. However, opinions vary on whether selection of an unconstrained TSR yields results that are better than or equal to hemiarthroplasty for shoulders with these characteristics.

Chronic synovitis, associated with RA and other types of synovium-based arthritis, tends to erode periarticular soft tissues in addition to the articular surfaces of a joint. As a consequence, a rupture or full-thickness tear of a rotator cuff tendon (typically the supraspinatus) develops in 25% to 40% of these patients and a rupture of the biceps tendon in an even greater percentage. If the soft tissues can be repaired and their functions improved, a semiconstrained TSR (standard or possibly a reverse ball-and-socket design) that may include bone grafting at the glenoid to improve prosthetic fixation may be indicated. If an effective cuff repair cannot be achieved or if there is insufficient bone stock owing to osteoporosis for fixation of a glenoid implant, hemiarthroplasty is usually the procedure of choice.

Hemiarthroplasty is often used when the articular surface and underlying bone of the humeral head have deteriorated but the glenoid fossa is reasonably intact, as seen with osteonecrosis of the head of the humerus. A patient with severe, chronic pain and loss of function as the result of a massive, irreparable cuff tear and subsequent development of a cuff tear arthropathy is typically a candidate for hemiarthroplasty. (The term “cuff tear arthropathy,” first used by Neer, refers to deterioration and eventual collapse of the head of the humerus, an infrequent but debilitating long-term result of a primary, massive and irreparable tear of the rotator cuff.) Chronic deficiency of the rotator cuff mechanism leads to superior migration of the head of the humerus in the glenoid fossa. If a glenoid component is inserted under these conditions, the superior migration creates an incongruous articulation that accentuates the risk of loosening and premature wear of the glenoid implant.

Operative Procedures
Total shoulder replacement and hemiarthroplasty are open surgical procedures performed with the patient in a semi-reclining position. The operative procedure involves the following components: anterior approach using a deltopectoral incision that extends from the AC joint to the deltoid insertion for adequate surgical exposure; release (tenotomy) of the subscapularis tendon from its proximal attachment on the lesser tuberosity; anterior capsulotomy; exposure of the humeral head for a humeral osteotomy; and preparation of the humeral canal for insertion of the prosthetic implant. The glenoid fossa is debrided and for a TSR is precisely contoured so the glenoid implant can be placed flush within the fossa.
Reconstruction and balancing of soft tissues is critical for optimal function after TSR and hemiarthroplasty. “Balancing” refers to the intraoperative lengthening or tightening of soft tissues to restore as near-normal resting tension in the tissues as possible, particularly in the rotator cuff, biceps, and deltoid muscle-tendon units.
Concomitant procedures that may be necessary during shoulder arthroplasty include:
• Repair of a deficient rotator cuff if the quality of the cuff tissue is sufficient

• Repair (reattachment) of the subscapularis and lengthening (medial advancement or Z-plasty) if a contracture significantly limits external rotation.

• Capsular plication and tightening for chronic subluxation or dislocation (usually posterior) of the GH joint.

• Anterior acromioplasty for a history of impingement syndrome.

• Bone graft of the glenoid if bone stock is insufficient for fixation of the glenoid implant.

After implantation of the prosthetic component(s) and repair of soft tissues but before closure of the skin incision, the shoulder is passively moved through all planes of motion to visually evaluate the stability of the prosthetic joint and the integrity of the repaired soft tissues. This determines the anatomical ROM possible after surgery and how aggressive the postoperative program can be.

Complications

Complications can occur after a wide variety of orthopedic surgeries. Although the incidence of intraoperative and postoperative complications after current-day arthroplasty is low, even a single complication can adversely affect the functional outcome. The incidence of complications tends to be higher in patients with a deficient rotator cuff mechanism, osteoporosis, and a preoperative history of chronic GH joint instability.

Postoperative Management

NOTE: Effective patient education and close communication among the therapist, surgeon, and patient are the basis of an effective and safe rehabilitation program individualized to address the specific surgical procedures used to meet the unique needs of each patient.

Special Considerations
Integrity of the rotator cuff. Regardless of the underlying cause of late-stage glenohumeral arthritis, the goals, components, and rate of progression of a rehabilitation program after TSR or hemiarthroplasty are influenced by the pre- and postoperative integrity of the rotator cuff mechanism. A deficient rotator cuff compromises the dynamic stability and kinematics of the GH joint, as demonstrated by upward riding of the humeral head leading to increased shear forces at the joint during active elevation of the arm.The rehabilitation program for a patient with an intact rotator cuff prior to shoulder arthroplasty can be progressed more rapidly than the program for a patient with coexisting rotator cuff deficiency requiring a concomitant cuff-tendon repair at the time of shoulder arthroplasty. The postoperative program for a patient with an irreparable rotator cuff or a tenuous repair due to poor tendon quality must be progressed even more cautiously.

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