Abstract
Mismatch of bearing component centres and tension of soft tissues surrounding the hip joint can lead to component separation during gait cycle and cause the femoral head to contact the rim of an acetabular liner, which could increase wear and shorten lifespan of an implant. This study aims to investigate the contact and wear mechanics of a metal-on-polyethylene hip joint under dynamic separation by using Finite Element Analysis (FEA).
A Pinnacle® cup with a Marathon neutral liner 36×56mm with a 45° inclination was constrained by a spring element in the medial-lateral axis. The spring was pre-compressed by 4mm to represent the corresponding translational mismatch of a simulator testing. Archard's law was used to predict wear over one ISO 14242-1 gait cycle.
Contact pressure is proportional to the load input during the stance phase, associated with concentric contact condition; it increases threefold just before the swing phase (time C), reaching 46.2MPa, where edge loading occurs. Consequently, separation climbs to 3.54mm, which is comparable to the mathematical prediction (3.34mm) and dynamic FEA (3.2mm). The predicted volumetric wear after this gait cycle is 1.22 × 10–5 mm3.
Dynamic separation between femoral head and acetabular liner can result in edge loading, consequently high contact pressure on the edge of a liner. In combination with cyclic loading, fatigue damage could take place and may be worth investigating in the future.
