[Principles of shoulder prosthesis implantation]

Patients with an intact rotator cuff and a humeral head that is centered in the glenoid fossa will benefit from both: a hemiarthroplasty and a total shoulder arthroplasty. However, the functional outcome following total shoulder arthroplasty is superior to that of hemiarthroplasty. Superior migration or mal-positioning of the humeral head in the anterior or posterior direction are generally associated with a maximum active flexion of 90 degrees and a high rate of loosening of the glenoid component. Total shoulder arthroplasty leads to superior results in patients with osteoarthritis and mal-positioning of the humeral head in the posterior direction. However, if the head can not be centralized in the glenoid fossa a significant risk of glenoid loosening remains. A superior functional outcome of total shoulder arthroplasty in patients with rheumatoid arthritis can be observed. On the other hand inferior bone quality and a rotator cuff might lead to loosening of the glenoid component. Radiographic signs of glenoid loosening are frequently observed. However, these hardly require operative revisions. If a glenoid component can not be inserted, a bipolar or inverse prosthesis might be considered an alternative.