CORRInsights®: Prediction of Polyethylene Wear Rates from Gait Biomechanics and Implant Positioning in Total Hip Replacement

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Polyethylene wear is a key factor in osteolysis and a determinant for subsequent revisions [6]. To combat polyethylene wear, researchers developed new materials such as highly-crosslinked polyethylene (HXLPE), which in turn, allowed for the use of large femoral heads. It appears that use of this material in practice has lowered the average wear rate. However, it is of particular interest to understand why certain patients have higher than expected wear rates and require revision surgery.
From a mechanical standpoint, wear is a function of the forces on the polyethylene, as well as the distance of travel of the femoral head against the polyethylene, the path of the femoral head, the location of force on the polyethylene, the roughness of the femoral head, and the properties of the polyethylene. In clinical terms, wear is a multifactorial problem that involves patient weight, activity level, gait, implant design, and implant positioning. The clinical and mechanical factors combine to generate wear.
To date, there is no method to predict polyethylene wear in a specific patient. There is not even a method to predict the wear of a previously untested material without the use of a hip wear simulator.
Despite the inability to accurately predict clinical wear, HXLPE has been shown to have wear rates of less than 0.03 mm/year at 14 years [5]. One systematic review [3] found lower wear rates among HXLPE liners (0.042 mm/year) compared to non-HXLPE liners (0.137 mm/year). At this time, there is little doubt that HXLPE wear rates are lower compared to non-HXLPE wear rates. However, there have been reports of osteolysis in low-wear (<.1 mm/year) HXLPE bearings [3, 7].

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