Outcome and risk of revision following shoulder replacement in patients with glenohumeral osteoarthritis

Glenohumeral osteoarthritis is a gradual, progressive wear and breakdown of articular cartilages and underlying bone with flatting of the humeral head and formation of marginal osteophytes. It may involve degeneration of soft tissue structures including the synovium, joint capsule, ligaments and adjacent rotator cuff tendons¹.

The incidence of glenohumeral osteoarthritis is unknown but it is, after the hip and knee, the third most common joint to require joint replacement². The incidence increases with age and glenohumeral osteoarthritis has an older average age of onset than hip and knee osteoarthritis³. For unknown reasons glenohumeral osteoarthritis is more often seen in women than in men³.

Glenohumeral osteoarthritis is divided into primary and secondary forms. The exact etiology of primary glenohumeral osteoarthritis is poorly understood but there are several risk factors including age, overweight, genetics, and occupations with heavy and/or overhead work⁴. Secondary glenohumeral osteoarthritis has a known etiology such as malunion of a proximal humeral fracture, instability (acute or recurrent dislocation) or a history of inflammation (rheumatoid arthritis or previous septic arthritis)⁴. Primary glenohumeral osteoarthritis is most prevalent, especially in patients over the age of 60. Younger patients are more often diagnosed with secondary glenohumeral osteoarthritis^4,5.

The pathological changes are initiated by a destruction of the articular cartilage changing the load distribution across the joint. This can lead to changes in the subchondral bone with flattening of the humeral head and/or glenoid wear. Loss of sphericity and concentricity can then result in a chronic posterior subluxation with an impaired range of motion. The range of motion can also be mechanically impaired by the formation of osteophytes around the glenoid and the humeral head (Figure 1). Soft tissue structures are often involved in glenohumeral osteoarthritis. Initially, the synovium is affected but in the later stages the joint capsule and the ligaments thickenings, and joint stiffness may lead to capsular contracture resulting in a further impaired range of motion. Adjacent rotator cuff tendons, especially the subscapularis tendon, can be affected with contracture secondary to a long-term disuse of the shoulder^{1, 3}.