Twelve-year risk of revision after primary total hip replacement in the U.S. Medicare population

Abstract

Background: There is limited population-based literature on rates and risk factors for revision following primary total hip replacement.

Methods: We performed a retrospective cohort study of Medicare beneficiaries who had elective total hip replacement for osteoarthritis between July 1, 1995, and June 30, 1996. Patients were followed with use of Medicare claims through 2008. The primary end point was revision total hip replacement as indicated by hospital discharge codes according to the International Classification of Diseases, Ninth Revision. We used the Kaplan-Meier method to plot the risks of revision and of death over a twelve-year follow-up period. We used Cox proportional hazard regression models to identify preoperative risk factors for revision of primary total hip replacement. We conducted sensitivity analyses to account for competing risks of major comorbid conditions.

Results: The risk of revision total hip replacement for patients remaining alive was approximately 2% per year for the first eighteen months and then 1% per year for the remainder of the follow-up period. The absolute risk of death over the twelve-year follow-up period exceeded the risk of revision total hip replacement by a factor of ten (59% vs. 5.7%) in patients older than seventy-five years at the time of primary total hip replacement and by a factor of three (29% vs. 9.4%) in patients sixty-five to seventy-five years old at the time of surgery. In multivariate Cox proportional hazard models, the relative risk of revision was higher in men than in women (hazard ratio [HR], 1.23; 95% confidence interval [95% CI], 1.15, 1.31) and in patients sixty-five to seventy-five years of age at the time of primary total hip replacement than in those over seventy-five years (HR, 1.47; 95% CI, 1.37, 1.58). Patients of surgeons who performed fewer than six total hip replacements annually in the Medicare population had a higher risk of revision than those whose surgeons performed more than twelve per year (HR, 1.21; 95% CI, 1.12, 1.32).

Conclusions: Efforts to reduce the number of revision hip arthroplasties should be targeted at revisions occurring in the first eighteen months following the index arthroplasty, when revision risk is higher, and at younger patients, who are more likely to survive long enough to require revision. .

Fig. 1-A. Kaplan-Meier curves showing the risk of revision total hip replacement among surviving patients.

The revision-free survival curve is stratified by age at the time of primary total hip replacement (sixty-five to seventy-five years of age compared with more than seventy-five years) and sex.

Fig. 1-B. Kaplan-Meier curves showing the risk of revision total hip replacement among surviving patients.

The revision-free survival curve is stratified by the annual volume of total hip replacements done by the surgeon who performed the primary total hip replacement (fewer than six, six to twelve, and more than twelve primary total hip replacements per year in the Medicare population).

Fig. 2-A. The proportion of patients who died over the course of follow-up (dotted area), those who had a revision (black), and those who were alive and at risk for revision (gray). The revision group includes those who remained alive and those who had a revision and then died.

Among patients who were sixty-five to seventy-five years old at the time of primary total hip replacement, the revised group comprised 9.4% of the original cohort; 29% had died.

Fig. 2-B. The proportion of patients who died over the course of follow-up (dotted area), those who had a revision (black), and those who were alive and at risk for revision (gray). The revision group includes those who remained alive and those who had a revision and then died.

Among patients who were more than seventy-five years old at the time of primary total hip replacement, the revised group (black) comprised 5.7% of the original cohort; 59% had died.