Bipolar implant shoulder arthroplasty: long-term results

The bipolar shoulder implant (BSI), designed by the senior author in 1975, has an unfixed metal glenoid cup with a polyethylene liner that articulates with a cemented titanium humeral component. The BSI was inserted in 35 shoulders of 33 patients with severe rheumatoid arthritis (20 cases), degenerative arthritis (ten cases), and posttraumatic lesions (five cases). The follow-up period ranged from 24 to 140 months (average, 63 months). Pain relief was good to excellent in 31 shoulders; four experienced some pain during daily activities. After BSI, motion was greatly improved with 71 degrees average range of abduction, 23 degrees range of adduction, 79 degrees range of flexion, 45 degrees range of extension, 76 degrees range of internal rotation, and 28 degrees range of external rotation. BSI was well-tolerated by the bone and soft tissues, with no erosive changes at the coracoacromial arch. There was no evidence of loosening at the cement-bone interface. One patient with a postoperative subcoracoid dislocation maintained a good functional result for more than 11 years. One BSI had draining sinus tract with negative culture, which spontaneously healed following removal of the implants. There were 3.3 mm (range, -7 mm to 11 mm) of superior subluxation of the humeral head on the preoperative roentgenogram. This increased to 8.7 mm (range, -5 mm to 20 mm) in the long-term follow-up roentgenogram. The bipolar implant is specially indicated in the severely arthritic shoulders in patients with vertical humeral subluxation and complicated histories of multiple failed operations.