Ankle alignment before and after total knee arthroplasty in patients with valgus knee deformity.

Background: The impact of Total Knee Arthroplasty (TKA) on the biomechanics of bilateral ankle joints with valgus knees remains unclear. This study aimed to evaluate how unilateral TKA affects bilateral ankle tilt, limb alignment, and biomechanics in knee valgus.

Methods: Among 105 patients with end-stage knee osteoarthritis and mild-to-moderate valgus deformity who underwent TKA between January 2021 and June 2023, 86 were included in the study retrospectively. The hip-knee-ankle angle (HKA), weight-bearing line ratio (WBLR), knee joint line convergence angle (KJLCA), knee joint line obliquity (KJLO), tibial anterior surface angle (TAS), tibial plafond inclination (TPI), talar inclination (TI), and tibiotalar tilt (TT) were measured on standing full-length lower limb radiographs preoperatively and postoperatively, with postoperative follow-up averaging 10.4 months. Patients were divided into Group A (0°~5°, 25 knees), Group B (5°~10°, 40 knees), and Group C (10°~15°, 21 knees) based on the degree of lower limb alignment correction. Additionally, patients were classified into contralateral knee varus (30 knees) and valgus (56 knees) groups based on the preoperative HKA angle of the contralateral knee.

Results: With changes in HKA, both TAS and TT showed concurrent change. Postoperative TAS [93.2 (86.9, 116.8)] and TT [-0.4 ( -5.9, 8.1)] showed a significant increase in absolute value compared to preoperative TAS [90.3 (83.1, 100.5)] and TT [0.2 ( -5.2, 6.4)] (P < 0.05). This suggests that TKA may alter the inclination angle of the talar articular surface by correcting the lower limb mechanical axis. Postoperative comparisons of ΔTPI and ΔTI across correction groups revealed statistically significant differences (P < 0.05). These findings indicate that greater knee deformity is associated with a larger preoperative angle between the distal tibial articular surface and the horizontal plane. Correction of severe deformities increases the postoperative TI angle, leading to a more inclined talar articular surface. No correlation was observed between preoperative and postoperative HKA and alignment of the contralateral ankle joint.

Conclusions: Before and after TKA, concurrent changes were observed in the ipsilateral ankle's inclination angle. For severe knee valgus deformities, maintaining a residual valgus deformity postoperatively should be considered to avoid postoperative ankle complications.