Relationship between polyethylene wear and osteolysis in hips with a second-generation porous-coated cementless cup after seven years of follow-up.

BACKGROUND: The development of osteolysis, a commonly reported complication after total hip arthroplasty without cement, is perceived to be related to the amount of polyethylene particles generated from the bearing surfaces. Although the literature has suggested that the prevalence of osteolysis increases with increasing rates of polyethylene wear, this relationship has never been quantified. The goals of this study were to quantify the relationship between the prevalence of osteolysis and both linear and volumetric wear and to evaluate the risk of osteolysis as a function of wear in a currently used, porous-coated cup design.

METHODS: Polyethylene wear and osteolysis were examined in fifty-six hips with a Duraloc-100 acetabular cup articulating with a 28-mm femoral head. Penetration of the prosthetic head into the polyethylene liner was measured, with use of a validated computer-assisted technique, from anteroposterior pelvic radiographs of each patient. From these measurements, linear and volumetric wear rates were calculated. Each patient's series of radiographs was examined independently for the presence of osteolysis. A logistic regression analysis was performed to determine the risk of osteolysis associated with a given change in linear or volumetric wear rate.

RESULTS: Osteolysis was found in twenty-three of the fifty-six hips. The hips with osteolysis had significantly higher linear (p < 0.001) and volumetric (p = 0.003) wear rates than the hips without osteolysis. Logistic regression revealed that every 0.1-mm/yr increase in the linear wear rate increased the likelihood of the development of osteolysis by a factor of four. Each 40-mm (3) /yr increase in volumetric wear raised the risk of osteolysis by about three times.

CONCLUSIONS: To our knowledge, this study represents the first time that the relationship between polyethylene wear, as determined by both linear wear and volumetric wear, and the prevalence of osteolysis has been quantified. The use of the linear wear rate as a predictor of osteolysis can be a valuable tool in assessing the longevity of a particular implant. The results of our analysis provide quantitative support to the observation that a wear rate of 0.2 mm/yr seems to represent a "critical threshold" for the development of osteolysis. Close radiographic monitoring with the determination of linear wear rates to assess the risk of osteolysis is recommended for all patients after total hip arthroplasty.