Metal-on-Metal Hip Resurfacing : The Effect of Cup Position and Component Size on Range of Motion to Impingement

The aim of this dry bone study was to determine the range of hip motion to impingement for different hip resurfacing cup positions and component sizes.The maximum angles of hip flexion, extension, abduction, and adduction were calculated from 3-dimensional coordinates for:1. Cup inclination of 30°, 40°, 50°, 60°, and 70° with fixed anteversion;2. Cup anteversion of 0°, 10°, 25°, 35°, and 45° with fixed inclination; and3. 3 different component sizes on the same size dry bones.An acetabular component inclination of 50° and an anteversion of 25° allowed the most physiologic range of hip motion. A larger-diameter femoral component relative to the native femoral neck diameter resulted in a greater range of hip motion to impingement.