Rheumatoid Arthritis Of The Glenohumeral Joint
Rheumatoid arthritis (RA) is an inflammatory disease based within the joint lining (synovium). This inflam- matory disease can be very destructive to the articular cartilage and bone but also affects the surrounding soft tissues. Shoulder RA specifically can cause severe thinning and then tearing of the rotator cuff and biceps tendon as well as progressive destruction of the articular cartilage on both sides of the joint.
Unlike osteoarthritis, RA is a nonproliferative arthritic condition and there is minimal new bone formation, resulting in minimal osteophyte formation. This feature is important in distinguishing between the two most common causes of shoulder arthritis. There can be progressive bone loss with osteopenia and demineralization of the humeral head. This is similar to patients with rotator cuff arthritis. Patients with osteoarthritis have hard bone that becomes whiter on radiography related to new bone formation. Glenoid bone loss is often centered within the glenoid fossa, resulting in medial migration of the humeral head. Osteoarthritis shows more eccentric glenoid wear primarily on the posterior glenoid. In many cases of rheumatoid arthritis, there is superior migration of the humeral head seen on radiographic views that is associated with destructive changes of the rotator cuff. Rheumatoid arthritis, rotator cuff tear arthritis, and crystal-induced arthritis (hydroxyapatite deposition disease, “Milwaukee shoulder”) produce large rotator cuff tears and superior migration of the humeral head, which, in turn, can result in asymmetric superior glenoid bone loss. All of these findings are best seen on routine radiographs. CT is also helpful in demonstrating these bone changes. The synovitis and joint effusion and the rotator cuff damage are best seen with MRI.
The humeral head can show lack of proliferative osteophyte formation but severe erosive changes of the articular surface. A treatment option for younger patients is a conservative humeral replacement maintaining most of the humeral bone stock using a surfaceonly arthroplasty (no stem). Avoidance of a glenoid prosthetic plastic component may be achieved by use of a meniscal allograft on the glenoid surface. This remains a controversial method of treatment because the results are not as consistent or predictable as those for traditional complete prosthetic joint replacement (total shoulder arthroplasty). These patients can be very young, and a traditional complete joint replacement can have its own difficulties with long-term survivorship, and a more conservative joint replacement avoiding the humeral stem and plastic glenoid prosthetic component can result in good clinical outcome and therefore remains a surgical treatment option for the young active patient.
More traditional treatment of rheumatoid arthritis when the rotator cuff is intact is anatomic total shoulder arthroplasty. The rotator cuff is intact, and this is treated with a cemented stemmed total shoulder arthroplasty. When the rotator cuff is damaged and there is associated superior migration of the humeral head, hemiarthroplasty is preferred over total shoulder replacement. With superior migration of the humeral head and anatomic total shoulder replacement, the prosthetic humeral head will remain superiorly displaced and will therefore contact only the superior part of the glenoid component, resulting in a continuous eccentric loading of the glenoid component. This will result in early loosening of the glenoid component. In some cases with severe rotator cuff deficiency a reverse total shoulder replacement is the best option to relieve pain and improve function related to rotator cuff deficiency, while avoiding the eccentric loading conditions of an anatomic-type shoulder replacement.
Many of the newer disease-modifying biologic drugs block the factors that result in the inflammatory mechanism that lead to joint destruction. For this reason the need for shoulder replacement in patients with rheumatoid arthritis has markedly decreased in the past 10 to 15 years.