The younger patient with advanced arthritis of the glenohumeral joint presents a difficult treatment problem, particularly when there are structural changes involving the glenoid. Severe pain and restriction of motion can occur, which is often refractory to nonoperative measures. In the early stages of the arthritic process, treatment alternatives such as arthroscopic debridement (1, 2, 3), synovectomy (4,5), capsular release (1,3,6), and glenoidplasty (7) may delay the onset of more severe symptoms and degenerative changes, but their role as definitive procedures is limited.

When severe damage to the glenoid exists, treatment options traditionally have been limited to glenohumeral arthrodesis or prosthetic replacement of the joint. Total shoulder joint arthroplasty results in predictable pain relief and probably the best functional outcome, but concerns about wear and loosening of the glenoid component raise the question of whether its implantation is appropriate in young patients (8). Arthrodesis can be a good alternative in high-demand patients requiring strength and stability; however, it continues to remain a salvage procedure when other surgical treatments have failed because of marked limitation of motion and potential pain from the scapulothoracic musculature (9, 10, 11).

Humeral head replacement alone has been the most common reconstructive procedure performed for this patient group. Pain usually is improved, but the results have been less favorable in terms of range of motion and strength, particularly when there is asymmetric wear or damage to the glenoid (8,12, 13, 14). Longer-term follow-up studies of patients treated with hemiarthroplasty have also shown that progressive glenoid bone erosion may occur, which can result in increasing pain (15,16).

In an attempt to improve the functional results and pain relief in younger patients with severe glenohumeral arthritis and glenoid involvement, hemiarthroplasty with soft-tissue interposition recently has generated interest. The aim is to provide a new biologic articulating surface for the humeral head prosthesis in the form of an interposition arthroplasty.

In this chapter the indications and contraindications for interposition arthroplasty of the shoulder are reviewed. Patient selection and preoperative evaluation are discussed, and the surgical technique is described for the
more commonly used interposition materials. A summary of the published results for interposition arthroplasty of the shoulder then follows.

The concept of interposition arthroplasty is not new. The earliest description in the United States was from Murphy in 1904, reporting on the use of fascia lata in the knee (17). The elbow has been a common site for interposition arthroplasty, with numerous reports in the literature showing good pain relief and improvements in range of motion (18, 19, 20, 21, 22). Several different interposition materials have been used, including Gelfoam, silicone, nylon, acrylic, skin, and animal membranes. Outside of the shoulder the most commonly used material has been autogenous fascia lata. It is easy to harvest and conforms readily to bony surfaces, but the donor site morbidity is a drawback.

Jones in 1942 was the first to report a technique of resurfacing the shoulder with fascia lata for complex proximal humerus fractures (23). Interposition arthroplasty also has been used in the severely damaged rheumatoid shoulder, using either lyophilized dura mater (24, 25, 26, 27) or a silastic (silicone) cup (28,29). Here we avoid the use of an implant initially, aiming to preserve bone stock for possible future prosthetic replacement (26).

In 1995 Burkhead and Hutton reported on biologic resurfacing of the glenoid combined with hemiarthro-plasty in young patients with end-stage glenohumeral arthritis (30). Biologic resurfacing of the glenoid was undertaken using either autogenous fascia lata or anterior shoulder capsule. The same authors later reported on this technique in revision shoulder joint replacement, when placement of another glenoid component was contraindicated (31).

In 2001 we described a new technique that involves hemiarthroplasty combined with resurfacing of the glenoid using a meniscal allograft (32). We hypothesized that a meniscal allograft would have several advantages compared with previously described interposition materials used in the shoulder. These include an established history for synovial based healing in the knee, improved structural characteristics for durability, and a wedge shape to compensate for preexisting glenoid wear.

Biologic resurfacing of the glenoid in conjunction with humeral head replacement is considered in select younger patients with incapacitating pain from end-stage glenohumeral arthritis in whom nonsurgical measures have failed. The best indication is a young, active patient in whom longevity of the glenoid component is a concern or a patient with asymmetric wear or structural damage to the glenoid where implantation of a glenoid component is not possible.

Interposition arthroplasty without humeral head replacement has been used in treating the rheumatoid shoulder with advanced stages of destruction (24, 25, 26). This avoids the use of an implant initially and may preserve bone stock for later prosthetic replacement, but despite initially acceptable results, the long-term outcome deteriorates with time (27). In younger patients with primary or posttraumatic arthritis, the results are also less favorable than when combined with hemiarthro-plasty.

Candidates for interposition arthroplasty must have failed an extensive trial of nonoperative therapy. They also must have failed or have been unsuitable for arthroscopic treatment of the shoulder joint. This includes debridement and capsular release, synovectomy, abrasion arthroplasty, or microfracture of the articular surfaces. Patients should be deemed less suitable for glenoid replacement because of young age and subsequent long-term wear and loosening concerns or inadequate glenoid bone stock, which precludes component implantation.

Interposition arthroplasty also can be used as a salvage procedure in revision shoulder joint replacement when loss of glenoid bone stock makes placement of another glenoid component impossible (31). Packing the defect with bone graft and covering the glenoid with fascia lata or reflected capsule helps to cushion the glenoid and also holds the graft in place (33). Interposition arthroplasty also has been used in cases of rotator cuff arthropathy (33,34). In these patients, pain relief may be improved initially, but with time the humeral head continues to migrate superiorly, resulting in eccentric loading and probable failure of the graft.