In-vivo postoperative motion analysis of metal and ceramic bipolar hip hemiarthroplasty.

Background: We hypothesized that ceramic bipolar shows less impingement between stem neck and outer head compared to metal bipolar, because of its low coefficient of friction with the acetabulum cartilage. In this paper, a three dimensional (3D) postoperative motion analysis has been used to assess the different motion characteristics of metal and ceramic bipolar hip hemiarthroplasty systems.

Methods: This study was conducted on 40 patients divided in two matched cohorts: 20 patients with metal bipolar and 20 patients with the ceramic bipolar. We obtained motion pictures from standing position to maximum abduction in flexion by fluoroscopy then analyzed by 2D-3D image matching method. The motion range of the "Outer head angle", "Stem neck angle" and the "Stem neck and outer head angle" was compared between the metal bipolar group and the ceramic bipolar group.

Results: The metal bipolar group's inner head's range of movement was greater than the ceramic bipolar group. Impingement between stem neck and outer head occurred in 30% of metal group patients. There were no impingement cases for the ceramic bipolar group.

Conclusions: The ceramic bipolar shows less impingement between stem neck and outer head compared to the metal bipolar. Ceramic bipolar may reduce the typical bipolar related complication and exert less effect on the acetabular cartilage due to less surface coefficient of friction.