Functional alignment alters axial rotation and flexion compared with mechanical alignment during intraoperative navigation-based assessment in total knee arthroplasty.

Abstract

This study compared intraoperative kinematics, radiographic characteristics, and patient-reported outcomes between functional alignment (FA) and mechanical alignment (MA) total knee arthroplasty (TKA) performed with computer-assisted surgery (CAS). This retrospective study included patients who underwent primary TKA using the same implant and navigation system. After 1:1 propensity score matching for age, sex, preoperative range of motion (ROM), and WOMAC pain score, 42 patients (21 FA, 21 MA) were analyzed. Intraoperative ROM, tibial rotation, femoral translation, and coronal limb alignment were recorded using the navigation system. Radiographic assessments included the hip-knee-ankle (HKA) angle, component orientation, and patellar tilt angle (PTA). Patient-reported outcomes were evaluated using WOMAC and pain visual analog scale (VAS) scores. Baseline characteristics were comparable after matching. Two-way mixed ANOVA demonstrated a significant main effect of group for tibial internal rotation (p < 0.001). Post hoc analysis revealed a significant between-group difference at maximum flexion (MA - FA = -3.4° ± 1.6°, p = 0.037). FA also demonstrated more varus coronal alignment (p = 0.002). Maximum knee flexion was greater in FA than MA (median 142° [135-145] vs 132° [125-141], p = 0.011). Radiographs showed a more medially inclined tibial component and greater PTA in FA, while HKA did not differ. WOMAC and VAS pain scores were similar between groups. Functional alignment was associated with greater intraoperative flexion and internal tibial rotation compared with mechanical alignment; however, short-term clinical outcomes were similar between groups.