Impingement after total hip arthroplasty related to prosthetic component selection and range of motion.

This study was designed to define the relationship between different combinations of prosthetic head diameters, neck lengths, and acetabular containment angles, and range of motion before component impingement. Three cadaveric pelves with attached lower limbs were mounted in their correct anatomic position. Acetabular and modular femoral stems were inserted into each of the six hips. For each combination of femoral head diameter, neck length, and acetabular liner overhang, the range of motion to impingement was measured in flexion, extension, abduction, adduction, external rotation, internal rotation, and internal rotation with 90 degrees hip flexion. These experiments suggest that the maximum range of motion before impingement can be attained by increasing the prosthetic head diameter and avoiding longer neck lengths with skirts. Acetabular liners with greater overhang decrease motion in all planes except flexion when the overhang is positioned posteriorly.