Does the coronal plane alignment of the ankle and subtalar joints normalize after total knee arthroplasty?

Abstract

Background: Total knee arthroplasty (TKA) alters the lower extremity alignment, potentially affecting adjacent joints such as the ankle and subtalar joints. However, the relationship between changes in hindfoot alignment and ankle osteoarthritis (OA) after TKA remains incompletely understood. The purpose of this study was to clarify whether ankle and subtalar alignment normalizes after TKA and to identify factors associated with persistent malalignment.

Methods: We retrospectively analyzed 331 patients who underwent unilateral mechanical alignment (MA) TKA for knee osteoarthritis. A control group of 40 healthy subjects was used to define normal alignment ranges. Whole-leg anteroposterior weight-bearing radiographs were obtained preoperatively and 2 months postoperatively. Alignment parameters included the hip-knee-ankle angle (HKA), tibiotalar tilt angle (TTA), tibial plafond inclination angle (TPIA), talar inclination angle (TIA), and hindfoot alignment angle (HAA). Pre- and postoperative values were compared using the Wilcoxon signed-rank test, and changes in the proportion of patients within the normal range were determined. Wilcoxon rank-sum tests and chi-squared tests were used for group comparisons, and multivariate logistic regression identified independent predictors of persistent malalignment.

Results: HKA improved after TKA (-12° to -2.0°), with corresponding improvements in TPIA (99° to 94°) and TIA (99° to 95°) (all p < 0.001), indicating a significant correction toward neutral alignment. The proportion of patients within normal range increased postoperatively from 16% to 85% for HKA, 26% to 67% for TPIA, 24% to 64% for TIA, and 65% to 73% for HAA. Multivariate analysis identified ankle OA (odds ratio [OR] = 6.62 for TTA), female sex (OR = 2.32 for TPIA; OR = 3.19 for TIA), and varus knee alignment (OR = 2.81 for TIA) as independent predictors of persistent malalignment.

Conclusions: MA-TKA facilitates partial normalization of coronal hindfoot alignment, particularly at the tibial plafond and talus. However, female sex, varus knee deformity, and pre-existing ankle OA independently limit full correction. These findings highlight the biomechanical interdependence between the knee and hindfoot and may guide surgical decision-making and patient-specific alignment strategies.

Keywords: Ankle osteoarthritis; Coronal alignment; Hindfoot alignment; Subtalar joint; Total knee arthroplasty.

Fig. 1

Flow diagram illustrating the patient selection process for this study

Fig. 2

Whole-leg anteroposterior weight-bearing radiographs obtained (A) preoperatively and (B) 2 months after total knee arthroplasty using a mechanical alignment technique. Global alignment of the lower extremity was assessed using the hip–knee–ankle (HKA) angle, defined as the angle between the mechanical axis of the femur (line a) and that of the tibia (line b)

Fig. 3

Radiographic measurements of morphometric parameters on whole-leg anteroposterior weight-bearing radiographs. Line (a) represents the mechanical axis of the tibia, (b) the subchondral plate of the distal tibial articular surface, (c) the subchondral plate of the medial malleolus articular surface, and (d) the line connecting the tips of both malleoli. The tibial anterior surface angle (TAS) is defined as the angle between lines (a) and (b), the tibial medial malleolus angle (TMM) is the angle between lines (a) and (c), and the tibial bimalleolus angle (TBM) is the angle between lines (a) and (d)

Fig. 4

Radiographic measurements of ankle and subtalar joint alignment parameters on whole-leg anteroposterior weight-bearing radiographs. Line (a) represents the mechanical axis of the tibia, (b) the subchondral plate of the distal tibial articular surface, (c) a tangent to the talar dome, (d) a horizontal reference line parallel to the ground, (e) a line perpendicular to the ground, and (f) a line extending from the lowest point of the calcaneus to the center of the talar dome. The tibiotalar tilt angle (TTA) is defined as the angle between lines (b) and (c), the tibial plafond inclination angle (TPIA) is the angle between lines (b) and (e), the talar inclination angle (TIA) is the angle between lines (c) and (e), and the hindfoot alignment angle (HAA) is the angle between lines (a) and (f)

Fig. 5

Postoperative changes in the proportion of patients falling within the normal range for each alignment parameter