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Will the Knee Outlive the Patient? Kaplan-Meier Systematically Overstates the Lifetime Risk of Revision After Total
Wayne Hoskins1,2,3, Charles A Gusho4, Kenrick Rosser1
1Department of Orthopaedics, Whangārei Hospital, Te Whatu Ora Te Tai Tokerau, Whangārei, Aotearoa New Zealand.
Background:
Lifetime revision risk after total knee arthroplasty (TKA) is usually estimated from Kaplan-Meier survivorship, which treats death as noninformative censoring and overstates revision incidence when competing mortality is substantial. The bias increases with age. We quantified the discrepancy between Kaplan-Meier and competing-risk estimates and derived the age- and sex-specific probability of dying with the original TKA.
Methods:
We analyzed 2,920 primary TKAs from a 15-year multisurgeon single-institution database linked to the New Zealand Joint Registry. Revision and death were modelled as competing events using Aalen-Johansen cumulative incidence functions and Fine-Gray subdistribution hazards, with patient-level clustering for bilateral cases. Kaplan-Meier estimates censoring death served as the benchmark. Cohort mortality was compared with the New Zealand population using standardized mortality ratios (SMRs) from 2017 to 2019 life tables.
Results:
There were 155 revisions and 525 deaths (median follow-up 7.4 years). The 15-year revision estimate was 8.3% by Kaplan-Meier versus 7.4% by competing-risk estimation overall, and 5.6% versus 3.0% in patients aged 85 years or older (relative overestimation >80%). At 10 years, cumulative incidence of revision was 5.7% (95% CI 4.8-6.7) versus 19.9% (18.2-21.8) for death, diverging with age (85 years or older: 3.0% versus 67.6%). 97% of patients aged 75 years or older died with the original TKA. Each 10-year age increment lowered the revision hazard (sHR 0.76, 0.61-0.94) and raised mortality (HR 2.33, 2.02-2.68). Cohort mortality was lower than the general population (SMR 0.73, 0.66-0.79). Among Māori, this relative advantage (SMR 0.66) was absent against the total population (SMR 1.11).
Conclusions:
Kaplan-Meier systematically overstates absolute lifetime revision incidence after TKA, most in older patients for whom competing mortality dominates. Age- and sex-specific competing-risk estimates provide more accurate preoperative figures and should be reported alongside Kaplan-Meier when presenting long-term revision risk.
Level Of Evidence:
Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.
