Predictors of flexion contracture progression following total knee arthroplasty: role of global sagittal alignment and patient age.

Background: Knee flexion contracture (KFC) progression after total knee arthroplasty (TKA) can significantly affect functional outcomes through disruption of the biomechanical knee-hip-spine kinetic chain. This study was conducted to investigate whether preoperative global sagittal alignment parameters, particularly the center of the acoustic meatus-sagittal vertical axis (CAM-SVA), could predict short-term KFC progression after TKA.

Methods: A retrospective case-control study was performed on 760 consecutive TKA cases, with 347 knees meeting inclusion criteria. KFC progression was defined as > 5° increase in knee flexion angle between immediate postoperative and final follow-up radiographs. Demographic factors and radiographic parameters were analyzed using univariate and multivariate logistic regressions. Patient-reported outcomes were assessed using the American Knee Society Score (AKSS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Potential sources of bias were addressed through standardized measurement protocols and inter-observer reliability testing.

Results: KFC progression was observed in 39 knees (11.2%), with mean progression of 8.0 ± 3.8° over 23.5 ± 13.1 months. Multivariate analysis revealed that CAM-SVA and age were independently associated with KFC progression (odds ratio: 1.02 [95% CI 1.01-1.04], p < 0.05; and 1.09 [95% CI 1.02-1.17], p < 0.01, respectively). At 12 months, the KFC progression group demonstrated significantly lower AKSS scores and higher WOMAC scores (p < 0.05) as compared to the nonprogression group.

Conclusions: CAM-SVA and advanced age were identified as independent predictors of KFC progression following TKA, supporting the hypothesis that global sagittal malalignment contributes to compensatory knee flexion through biomechanical interdependence of the knee-hip-spine kinetic chain. Assessment of preoperative global sagittal alignment may help identify patients at risk for KFC progression and inform individualized treatment strategies.