A radiographic evaluation of birotational head motion in the bipolar shoulder hemiarthroplasty.

The concept of bipolar hemiarthroplasty has been described in the hip for more than 20 years, its role being to decrease acetabular wear. Shoulder bipolar hemiarthroplasty was described shortly afterward. The purpose of this study was to determine if the prosthesis acted as a bipolar device moving primarily at the inner metal on polyethylene bearing as intended, or as a unipolar hemiarthroplasty moving at the outer metal on glenoid surface articulation.