A radiological study of the intraprosthetic movements of the bipolar shoulder replacement in rheumatoid arthritis.

A radiological study of the intraprosthetic movements of a bipolar shoulder replacement was undertaken in 25 shoulders in 20 patients with rheumatoid arthritis and rotator cuff arthropathy. No significant difference was found between intraprosthetic movement and shell - glenoid movement. Some shoulders were found to exhibit paradoxical movement at the intraprosthetic interface. Repeating the measurements after an interval of three years in a subgroup of 12 shoulders showed a significant reduction in intraprosthetic movement over this time interval. In conclusion, movement of the bipolar shoulder prosthesis in shoulders affected by rheumatoid arthritis was preserved up to eight years from operation. Intraprosthetic movement was independent from shell - glenoid movement and paradoxical to glenohumeral movement.