The concept of bipolar hemiarthroplasty has been described in the hip for over twenty years, its role being to decrease acetabular wear. Shoulder bipolar hemiarthroplasty is a more recent concept. The purpose of this study was to determine if the prostheses 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 cartilage surface.

Eleven bipolar shoulder hemiarthroplasties with a minimum follow up of twenty two months were examined fluoroscopically. The proportion of arm abduction occurring in the scapulothoracic plane as well as that between the two components of the bipolar hemiarthroplasty was assessed and compared to that of normal patients and those with total shoulder replacements, previously reported in the literature.

The results of this study show that the majority of movement occurring in active arm abduction occurred in the scapulothoracic plane and that the bipolar hemiarthroplasty acted predominantly as a unipolar device.