Kinematic alignment, but not mechanical alignment, preserves the knee-ankle relationship after total knee arthroplasty: A retrospective radiographic analysis from the FP-UCBM Knee Study Group.

Abstract

Several alignment strategies have been proposed in total knee arthroplasty (TKA), with the two extremes being mechanical alignment (MA) and unrestricted kinematic alignment (KA). While MA standardises coronal knee parameters to achieve a neutral alignment, KA reproduces each patient's native joint lines. The impact of these strategies on the ankle joint remains poorly understood. The aim of this study was to compare the effects of MA and KA on coronal ankle alignment, hypothesising that MA induces greater alterations than KA. In this retrospective cohort study, 208 consecutive TKA cases, performed with either MA (n = 104) or unrestricted KA (n = 104) were included. Preoperative and 1-year postoperative full-length standing radiographs were analysed for lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), hip-knee-ankle angle (HKA), Coronal-Plane-Alignment-of-the-Knee (CPAK) categories and ankle-specific parameters: talar inclination (TI), tibial plafond inclination (TPI), and talar tilt (TT). Changes in radiographic parameters (Δ) were calculated as the difference between 1-year postoperative and preoperative values. Within-group and between-group changes were assessed with paired and independent t-tests, respectively, and correlations between knee and ankle changes were calculated. Statistical significance was set at p < 0.05. MA resulted in significant postoperative changes in TI (-3.21 ± 3.28°; p < 0.001) and TPI (-2.62 ± 3.16°; p < 0.001), whereas KA produced no significant changes (TI: -0.60 ± 3.54°, TPI: -0.18 ± 3.23°; p > 0.05). No significant changes were observed for TT in either group. In the MA group, ΔTPI correlated moderately with ΔHKA, ΔLDFA, and ΔMPTA. Pre/postoperative changes in CPAK category did not show any impact on coronal ankle parameters following TKA (p > 0.05) CONCLUSIONS: Coronal ankle alignment is preserved by unrestricted KA but altered by MA. These findings suggest that KA minimises unintended ankle alterations, maintaining the patient-specific knee-ankle relationship and potentially reducing the risk of secondary ankle malalignment or degeneration following TKA. Level IV, retrospective analysis.