Overestimation of the risk of revision with Kaplan-Meier presenting the long-term outcome of total hip replacement in older patients

Mortality as a competition risk factor in the survival analysis of the results of the type of fixation of the total hip prosthesis in octogenarian patients

INTRODUCTION

Total hip replacement (THR) is challenging in octogenarians due to associated comorbidities and controversy regarding fixation type. We ask whether cemented THR is superior to uncemented THR in patients above the age of 80 years.

MATERIAL AND METHODS

A total of 382 patients (441 hips) aged 80 years or older who underwent THR between 2004 and 2015 were analysed. A cemented THR was implanted in 196 hips (group 1), an uncemented THR with a grit-blasted stem in 121 (group 2), or with a porous-coated stem in 124 (group 3). Patients in group 1 had a higher mean age, more comorbidities and osteoporotic bone. Survival analysis was calculated using cumulative incidence function to account for the competing risk of death.

RESULTS

Medical complications rate was similar. There were 3post-operative fractures: one in group 2 and 2in group 3. Competing risk analysis showed that the cumulative incidence of revision for any cause was 2.3 in group 1, 6.0 in group 2 and 4.1 in group 3 at 10years, and the cumulative incidence of revision for aseptic loosening was 1.2 in group 1, 3.7 in group 2 and 0 in group 3 at the same period.

CONCLUSIONS

THR presents an acceptable number of adverse events for octogenarian patients. Despite uncemented fixation was satisfactory, the higher peri-prosthetic fracture rate worsens results in this group.

Are competing risks models appropriate to describe implant failure?

Background and purpose - The use of competing risks models is widely advocated in the arthroplasty literature due to a perceived bias in comparison of simple Kaplan-Meier estimates. Proponents of competing risk models in the arthroplasty literature appear to be unaware of the subtle but important differences in interpretation of net and crude failure estimated by competing risk and Kaplan-Meier methods respectively. Methods - Using a simple simulation we illustrate the differences between competing risks and Kaplan-Meier methods. Results - Competing risk and Kaplan-Meier methods estimate different survival quantities, i.e., crude and net failure respectively. Estimates of crude failure estimated using competing risk methods will be less than net failure as estimated using Kaplan-Meier methods. Interpretation - Kaplan-Meier methods are appropriate for describing implant failure, whereas crude survival estimated using competing risk methods estimates the risk of surgical revision as it depends on both implant failure and mortality. Both competing risk models and Kaplan-Meier methods are useful in arthroplasty, and both provide unbiased estimates of crude and net failure in the absence of any confounding or selection respectively. Surgeons and researchers should carefully consider whether the use of competing risks is always justified. Lower estimates of failure from competing risk models may be misleading to surgeons who are attempting to select the best implants with the lowest failure rates for their patients.