Correlation of Wear and Mechanics for Subjects having a Metal-on-Polyethylene Total Hip Arthroplasty Measured in vivo

Femoral head separation from the acetabular shell has been recorded, but clinical significance of this phenomenon has not yet been established. The objective of the study was to determine if there is a correlation between femoral head separation (sliding of the femoral head away from the acetabular cup), hip joint forces, and acetabular liner wear. Twenty subjects were strategically selected to participate in this study. All subjects were asked to perform gait on a treadmill while under fluoroscopic surveillance. The number of incidences involving femoral head separation was tallied and acetabular bearing surface forces were determined for each subject. A statistical correlation was done to
determine if femoral head sliding is related to the kinetics of the hip joint. Forty percent of the subjects were determined to have greater than 0.25 mm of wear. Twelve subjects demonstrated femoral head sliding leading to separation. Ten percent of the subjects tested demonstrated both wear and separation. The forces determined at the hip joint ranged from 1.75 to 1.85 times body weight. Although it was expected that subjects having more wear would have greater magnitudes of femoral head separation, the opposite was true. Kinematic data resulted in increased force magnitudes for a subject with separation then a subject with separation.