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Abstract: Knee wear is commonly measured with the most recent radiograph based on the assumption that wear progresses at a constant rate. Changing patient activity or in vivo polyethylene deterioration are examples of factors that could cause wear rates to change over time. Using six or more radiographs on each of 251 knees over a mean 10-year follow-up, we determined the pattern of polyethylene wear. 92% of knees had linear wear with a mean wear rate of 0.09±0.12 mm/yr. Ten knees (4%) had late accelerated wear. Knees with accelerated wear and those with a wear rate of 0.15 mm/yr or greater had lower survivorship rates. We conclude that wear is linear with rare exceptions and that higher wear is correlated with failure. [Copyright &y& Elsevier]

Abstract: Tibial articular cartilage wear was assessed intraoperatively in 100 consecutive patients with varus osteoarthritis undergoing total knee arthroplasty. Severity of deformity on radiographs, integrity of the anterior cruciate ligament (ACL) at surgery, and body mass index were recorded. Posterior half of the medial tibial plateau was more commonly involved in knees with ACL deficiency; there was predominantly anteromedial involvement with an intact ACL. Varus deformity was significantly greater in knees with a deficient ACL than with an intact ACL. Severity of deformity did not alter the wear pattern, irrespective of the ACL integrity. The functional status of ACL in an osteoarthritic knee can be corroborated with the wear pattern on the tibial plateau articular cartilage. [Copyright &y& Elsevier]

This paper presents an analytical model of the cobalt-based alloy-ultra-high molecular weight polyethylene (UHMWPE) wear coupling. Based on a previous model in which the cup wear volume over a gait cycle (WG) was calculated under the simplifying assumption of an ideal rigid coupling, the current version proposes a more realistic wear simulation. All three components of the hip loading force were considered for the contact pressure calculation and all three components of the hip motion were taken into account for the sliding distance calculation. The contact pressure distribution was calculated on the basis of the Hertzian theory for the elastic contact of two bodies with non-conforming geometrical shapes. The wear factor was taken from hip simulator wear tests. The calculated WG is 67 x 10(-6) mm3 for a standard reference patient. The parametric model simulations show that WG increases linearly with the patient weight, femoral head diameter and surface roughness. It increases non-linearly to a maximum and decreases to an asymptotic value with increasing cup/head clearance and with cup isotropic elastic modulus. The cup orientation in the pelvis affects only slightly the total amount of WG whereas it is the dominant factor affecting the shape of the wear distribution. The iso-wear maps show paracentral patterns at low cup inclination angles and marginal patterns at higher inclination angles. The maximum wear depth is supero-posterior when the cup is in neutral alignment and supero-anterior at increasing anteversion angles. Complex patterns with a combination of paracentral and marginal wear were obtained at specific clearance values and cup orientations. The results of the simulations are discussed in relation to the wear distribution measured on the articular surface of 12 UHMWPE components retrieved from failed hip joint prostheses, after a period of in situ functioning. [ABSTRACT FROM AUTHOR]