Abstract
PURPOSE: The purpose of this study was to compare preservation of posterior condylar offset (PCO) and posterior condylar offset ratio (PCOR) after medial pivot (MP) total knee arthroplasty (TKA) performed with kinematic (KA) or mechanical alignment (MA), and to assess whether changes in these parameters associate with 2-year clinical outcomes. METHODS: This post hoc radiographic analysis of a prospective randomised trial included 200 patients (100 KA, 100 MA). PCO and PCOR were measured on standardised pre and postoperative lateral radiographs. Postoperative values were compared between groups using analysis of covariance, adjusting for preoperative measurements. Associations between changes in PCO/PCOR and 2-year patient-reported outcome measures (PROMs) and range of motion (ROM) were assessed in a subset of 100 patients using multivariable models. RESULTS: Two hundred patients were included radiographically (MA 100, KA 100; mean age 68.9 ± 9.2 years). Adjusted between-group differences were 1.23 mm for postoperative PCO (90% confidence interval [CI]: -0.10 to 2.56; p = 0.13) and 0.023 for postoperative PCOR (90% CI 0.003 to 0.043; p = 0.06). Equivalence within ± 2.0 mm (PCO) and ± 0.02 (PCOR) was not demonstrated. Change-score analyses were concordant (ΔPCO difference 1.02 mm; 90% CI: -0.50 to 2.54; p = 0.27; ΔPCOR difference 0.026; 90% CI: -0.012 to 0.064; p = 0.26). In 100 patients with complete paired radiographic and 2-year clinical data, ΔPCO/ΔPCOR showed no significant associations with PROMs or ROM after adjustment. Interobserver reliability was excellent (intraclass correlation coefficient [ICC] 0.93 for PCO; 0.89 for PCOR). CONCLUSION: In MP TKA, KA and MA did not differ significantly in preserving PCO or PCOR; however, statistical equivalence within prespecified margins was not established. Changes in PCO/PCOR were not associated with 2‑year outcomes, suggesting that precise surgical execution, including specific rotational strategies, rather than alignment philosophy alone, is key to maintaining posterior femoral geometry in this implant design. LEVEL OF EVIDENCE: Level III, post hoc analysis of data from a randomised controlled trial.