Abstract
The aim of this study was to determine whether there is evidence to support the [often quoted] concept of a threshold effect of implant wear rate on osteolysis risk after total hip arthroplasty (THA). The study design was a case control study of 115 subjects with osteolysis after Charnley THA for idiopathic osteoarthritis (mean age at primary surgery 61.1 years; M:F =49:66; osteolysis-free survival 10.9 years) compared with 115 individually case-matched subjects following Charnley THA for idiopathic osteoarthritis with no current radiographic evidence of osteolysis (mean age 61.3 years; M:F = 49:66; osteolysis-free survival 11.0 years).
Calculated median (interquartile range) annual linear wear rate (measured using the EBRA method) was 0.12mm (0.08 to 0.18) and 0.07mm (0.05 to 0.10) in the osteolysis and control groups, respectively (Wilcoxon, P< 0.001). Subjects were divided into wear quintiles based on wear rate (n=46 subjects per quintile). The proportions of osteolysis subjects in each successive wear quintile groups were 0.22, 0.39, 0.48, 0.61, and 0.80 (χ2 P< 0.001). The proportion of subjects with osteolysis thus increased in a uniform manner with no evidence of a disproportionate increase between groups. The odds-ratio for osteolysis for each incremental increase in annual linear wear above the median wear rate in the control subjects was 2.4 (logistic regression analysis, 95% CI 1.7 to 3.3, P< 0.001).
In summary, the proportion of subjects with osteolysis increases steadily by wear quintile. Our data suggest a continuous gradient of risk for osteolysis associated with increasing annual wear rate in the Charnley prosthesis. We found no evidence to support the concept of a defined threshold above which the risk of osteolysis is disproportionately increased. The implication of this finding is that the goal of advances in bearing surface technologies should be aimed at the elimination of wear, rather than simply it’s reduction to below an arbitrarily-defined level
The abstracts were prepared by Mr Peter Kay, Editorial Secretary. Correspondence should be addressed to British Hip Society, The Hip Centre, Wrightington Hospital, Appley Bridge, Wigan, Lancashire WN6 9EP.
