Joint line obliquity disruption negatively affects mid‐term patient‐reported outcomes following total knee arthroplasty

PURPOSE: The influence of change in coronal alignment on clinical outcomes following total knee arthroplasty (TKA) remains unclear. The Coronal Plane Alignment of the Knee (CPAK) classification can be broken up into arithmetic hip-knee-ankle (aHKA) angle and joint line obliquity (JLO) components, potentially identifying distinct failure mechanisms. This study investigated the influence of change in the magnitude and surgical accuracy of CPAK on patient-reported mid-term outcomes and the risk of aseptic revision. METHODS: This retrospective cohort study included 216 patients (234 TKAs, median age 66 years, 65.3% women) undergoing patient-specific instrumentation in TKA with a minimum follow-up of 5 years. The change in CPAK was divided into aHKA and JLO components. Surgical accuracy was defined as deviation from the planned HKA angle. The primary outcome was the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). A secondary outcome was aseptic revision of TKA. Multi-stage method robust regression and logistic regression models were used, after adjustment for preoperative WOMAC scores and reintervention. RESULTS: The median WOMAC score improved from 50 (interquartile range [IQR] 24.3) preoperatively to 11 (IQR 19) postoperatively. Our analysis of change in CPAK components revealed JLO disruption as the primary predictor associated with inferior outcomes, with each step change associated with worse WOMAC scores (β = 3.98, p = 0.02) and increased revision risk (odds ratio = 3.15, p = 0.04). In contrast, change in aHKA was not associated with either outcome. CONCLUSION: Within the CPAK framework, JLO disruption emerged as the primary predictor of patient-reported inferior outcomes and risk of aseptic revision following TKA. Our current findings highlight the importance of preserving native JLO within personalized alignment strategies. Future prospective studies are needed to establish the acceptable degree of JLO change that maintains optimal joint kinematics and patient satisfaction. LEVEL OF EVIDENCE: Level III.