Effects of ball head diameter and stem neck shape in range of motion after total hip arthroplasty: A simulation study.

Simulations using three-dimensional computer-aided design were performed with the various conditions to research the movement distance of the ball head and total range of motion until impingement and dislocation (ROM(t)) which involved in joint stability. Although a large ball head increases the entire ROM(t) and oscillation angle, it decreases stability transitioning from impingement to dislocation. Conversely, though large neck diameter increases the simulated stability from impingement to dislocation, it reduces the ROM(t) and oscillation angle. ROM(t) decreases with change in neck shape and is greatly affected by the presence of osteophytes, even if the head-neck ratio remains the same.