Stemmed Tibial Fixation for Primary Total Knee Arthroplasty in Obese Patients—A National Registry Study

Introduction We aimed to determine if the use of augmented tibial fixation with stems in primary total knee arthroplasty (TKA) in obese patients was associated with a difference in the reason for revision, type of revision, or the overall revision rate. Methods Data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) compared reason for revision, rate, and type of revision between primary TKA using stemmed tibial prostheses to non-stemmed prostheses, stratified by body mass index (BMI) and obesity. The cumulative percent revision (CPR) was obtained using the Kaplan-Meier method, and Cox proportional hazards models estimated hazard ratios (HRs) adjusted for age and sex, with 95% confidence intervals. All tests were two-tailed at 5% statistical significance (P<0.05). P values are capitalized and italicized throughout the manuscript and tables. There were 66,508 procedures were available for analyses. Results Obese Class 2 (BMI 35 to 39.99) had higher rates of revision in the stemmed group compared to the no stem group (Hazards Ratio (HR) 1.44, 95% Confidence Interval (CI) 1.00, 2.05, P=0.047). There was no significant difference in revision rates between stemmed and non-stemmed tibial prostheses in any other BMI group. Primary TKA in obese patients (BMI ≥30), with a stem extension had a significantly higher rate of minor revisions compared to no stem extension (HR 1.31 95% CI 1.03, 1.66, P=0.025). There was no significant difference between stemmed and no stem groups for major revision in obese patients, and for minor or major revision in non-obese patients. Conclusion Using a tibial stem during primary TKA in obese patients is not associated with a lower rate of revision.