Pre- and Postoperative Alignment of the Knee Impacts Ankle Alignment: Analysis of 4,698 Total Knee Arthroplasties

Limited data exist on the effects of total knee arthroplasty (TKA) on ankle alignment. This large-scale study aimed to assess preoperative and postoperative ankle alignment in patients undergoing TKA using long-leg radiographs.

This retrospective single-center study analyzed 4,698 radiographs from patients undergoing mechanical alignment TKA. Included patients had a median age of 71 years (range, 31.8 to 95.0) and a mean body mass index of 29.9. Patients were grouped by preoperative and postoperative hip-knee-ankle (HKA) angles. Outcomes were ground-to-tibial plafond (GP), ground-to-talar dome (GT), and talar tilt (TT) angles. Propensity score matching, followed by weighted linear regressions, was used to assess the influence of HKA on ankle angles.

Preoperative angles showed a similar pattern, from 10.8 ± 3.8, 10.1 ± 4.3, and 10.5 ± 5.3 degrees in the severe valgus group to -12.5 ± 2.3, -5.2 ± 3.5, and -5.6 ± 4.3 in the severe varus group for HKA, GP, and GT, respectively. A strong correlation was observed between preoperative HKA and GP and GT across all groups (P < 0.001). Preoperative HKA significantly predicted postoperative GP and GT in most groups (P < 0.001). Among patients who had normal postoperative HKA, those who had preoperative valgus HKA showed higher postoperative GP and GT angles than those who had preoperative varus HKA. Postoperative HKA was also a strong predictor of postoperative GP and GT (P < 0.001). Talar tilt was largely unaffected by HKA, and neither body mass index nor age significantly influenced the angles.

Ankle alignment, defined by GP and GT, is strongly influenced by both preoperative and postoperative knee alignment, with preoperative HKA affecting postoperative ankle alignment even when normal postoperative HKA is achieved. The unaffected TT may indicate that alterations in GP and GT represent coordinated shifts of the entire distal ankle.