Polyethylene wear at the bearing surface of total hip prostheses can result in an inflammatory response that leads to periprosthetic osteolysis and aseptic loosening. Studies have demonstrated a reduction in wear in polyethylene with a more highly cross-linked molecular structure. The purpose of this study was to compare polyethylene wear on the basis of femoral head penetration in total hip prostheses with cross-linked polyethylene (XLPE) with those of standard polyethylene (non-XLPE). Femoral head penetration was evaluated in 74 patients. All hips were cemented stems with polished collarless prostheses and 28 mm CoCr femoral heads. Acetabular components were cementless hemispherical sockets with either XLPE or non-XLPE. The arthroplasties were performed because of degenerative joint disease in 54 hips, avascular necrosis in 8 hips, hip fracture in 4 hips, RA in 3 hips, psoriasis in 2 hips, AS in 1 hip, RA/AVN in 1 hip, and RA/fx in 1 hip. Linear polyethyelene wear was measured using the Livermore technique on standardized anteroposterior pelvic radiographs. The relationships between femoral head penetration (FHP) and implant material, gender, patient weight, and socket inclination were examined. Overall, the mean difference in FHP during the first year was not statistically significant when XLPE was compared with non-XLPE (p = .54). However, the comparison of FHP after the first year found that the FHP was lower for XLPE (p = .04). There were no significant differences in comparing FHP both during and after the first year by material and gender. The observed FHP for non-XLPE was greater than for XLPE both during and after the first year in males but only after the first year in females; however, the difference was not significant. Age has a significant negative relationship with FHP during the first year. The correlation between socket inclination and FHP was weak and not statistically significant (Rxy = .12, p = .307). These findings suggest that steady-state wear rates may be less in XLPE compared with non-XLPE after bedding-in has occurred in the first year. Bedding-in is a slow, plastic deformation in the direction of prevailing stress of the polyethylene and/or settling in of the liner. Radiographic methods for the assessment of polyethylene wear on the basis of femoral head penetration must be further developed to differentiate between plastic deformation of the polyethylene and actual polyethylene wear.
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