Management of Glenohumeral Arthritis.

Last updated Wednesday, January 09, 2008

Figure 54

Figure 55

Figure 56

Special considerations in arthroplasty

Degenerative joint disease

Rheumatoid arthritis

The basic principles of shoulder arthroplasty in rheumatoid arthritis are similar to those in degenerative arthritis, but some important differences exist. Rheumatoid tissues are much more fragile. The bone is more prone to fracture, and the muscle and tendons are more prone to tear. Thus, from the outset, extreme care must be taken to preserve bone and soft tissue integrity. We refer to these requirements for extraordinary gentleness as "rheumatoid rules."

Because rheumatoid arthritis is an erosive and destructive disease, tissue deficiencies of the bone and rotator cuff are more likely than in degenerative joint disease. Thus, the soft tissues anteriorly may be insufficient to allow for a subscapularis lengthening. The glenoid bone may be so eroded that there is insufficient stock to support a glenoid component. The rotator cuff may be partially or totally deficient. Thus, in the preoperative evaluation and in discussion with the patient concerning the possible outcomes of surgery, all of these factors need to be considered.

The standard preoperative scapular anteroposterior and axillary radiographs are required to evaluate the humeral and glenoid bone stock. In rheumatoid arthritis the glenoid erosion is usually medial (rather than posterior as in degenerative joint disease). For this reason, only minimal glenoid reaming may be necessary to achieve an excellent quality fit to the back of the glenoid component. The potential fragility of the bone and soft tissues makes it particularly important that the joint not be overstuffed, and that adequate soft tissue laxity be present for immediate postoperative motion. This is particularly a challenge in diminutive patients with juvenile rheumatoid arthritis who may also have a tiny humeral medullary canal. In some cases there may be insufficient joint volume to permit the insertion of a glenoid component in spite of complete soft tissue releases.

Secondary degenerative joint disease

In posttraumatic arthritis, the challenges may be even greater. The anatomy is likely to be distorted by previous fracture and surgery. The nonarticular humeroscapular motion interface is likely to be scarred, obscuring important neurologic structures, such as the axillary nerve. The tuberosities, the humeral shaft, and the glenoid may be ununited or malunited.

As a first step, the motion interface must be carefully freed, and the axillary nerve identified both as it crosses the subscapularis and as it courses laterally on the deep surface of the deltoid. Case by case judgments must be made concerning the need for osteotomy to try to restore more normal anatomic relationships, recognizing that additional healing and postoperative protection may be required. Again, the goal is restoration of anatomic relationships, firm fixation of components, soft tissue balance, stability, and smooth gliding in the humeroscapular motion interface.

Capsulorrhaphy arthropathy

Cuff tear arthropathy

In this condition there are several unique challenges for regaining glenohumeral smoothness. The humeral head is subluxated in a superior position so that it is articulating with the coracoacromial arch. The rotator cuff is almost never amenable to a strong repair, and the glenoid is eroded superiorly, so that an acetabular-like structure is formed in continuity with the coracoacromial arch. Under these circumstances, normal glenohumeral relationships are very difficult to normalize and maintain by a durable cuff reconstruction. More often it is preferable to accept the altered joint relationship which uses the "acetabulum" for secondary stability in the absence of primary stability from the rotator cuff. In this "special hemiarthroplasty," the articular surface of the proximal humerus is resurfaced with a component matching the preoperative humeral joint surface size and position. The tuberosities are smoothed so that they are congruous with the humeral articular surface. This allows for the proximal humerus to match the "acetabulum," and to articulate smoothly within it. It is very important to avoid using "oversized" humeral components, because they overstuff the joint, do not match the concavity of the "acetabulum" and restrict joint motion. In a special hemiarthroplasty, the patient is spared the necessity of protecting a rotator cuff repair, so that immediate passive and active exercises can be instituted after surgery. The patient is also spared the risk of glenoid loosening from the rocking horse mechanism (see figure 56).

The ideal patient for this procedure has a normal deltoid muscle, a concentric coracoacromial "acetabulum" stabilizing the proximal humerus, which is superiorly displaced with respect to the glenoid, concentric erosion of the upper glenoid fossa, a "femoralized" upper humerus with rounding off of the greater tuberosity, an irreparable rotator cuff defect, no previous surgical compromise of the acromion or coracoacromial ligament, good patient motivation, and realistic expectations.

In a series of ten patients having special hemiarthroplasty for rotator cuff tear arthropathy, the range of active motion and function were substantially improved by this procedure (Table 16-20). These results are not be as good as those for total glenohumeral arthroplasty because the patient lacks the benefit of both prosthetic glenoid smoothness as well as the function of the rotator cuff.

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