The effect of contact stress on cartilage friction, deformation and wear

Following hip hemiarthroplasty, a metal femoral head articulates against natural
acetabular cartilage. Cartilage friction and wear may be influenced by variables including loading time, contact stress, contact area, sliding distance, and sliding speed. The aim of this study was to investigate the effect of these variables on cartilage friction, deformation and wear in a simulation using idealized geometry model. Bovine cartilage pins were reciprocated against metal plates to mimic a hemiarthroplasty articulation under static loading. The effective coefficient of friction (meff) under contact stresses (0.5 to 16 MPa), contact areas (12 and 64mm2), stroke lengths (4 and 8mm), sliding velocities (4 and 8 mm/s), and loading time (1 and 24 hours) were studied. The permanent deformation of artilage (after 24 hours of recovery) with and without motion was recorded to assess cartilage linear wear. The meff was found to remain ,0.35 with contact stresses (4 MPa. Severe damage to the cartilage occurred at contact stresses .8MPa and significantly increased meff after 12 hours of reciprocation. In long-term, contact area had no significant effect on meff, and sliding distance and velocity only affected meff under low contact stresses. The cartilage linear wear increased with contact stress, sliding distance and velocity.