Preoperative Arithmetic Hip-Knee-Ankle Angle as a Predictor of Postoperative Leg Alignment in Medial Oxford Unicompartmental Knee Arthroplasty

TL;DR

This study shows that a preoperative angle measurement can predict postoperative leg alignment after a specific type of knee surgery.

Contribution

The study demonstrates that the preoperative arithmetic hip-knee-ankle angle is a reliable predictor of postoperative leg alignment in Oxford unicompartmental knee arthroplasty.

Findings

Preoperative aHKA was similar to postoperative mHKA with a small difference of −0.38° ± 2.96°.

The joint line obliquity showed a significant medial incline after surgery.

MPTA tended to be varus and LDFA tended to be valgus postoperatively.

Abstract

Introduction

This study aimed to evaluate whether the arithmetic hip-knee-ankle angle (aHKA) can be used to predict the postoperative HKA.

Methods

This study included 248 knees in 166 patients who underwent Oxford unicompartmental knee arthroplasty (UKA) between February 2021 and November 2022. Through preoperative and postoperative long-leg radiography, the medial proximal tibial angle (MPTA) and the lateral distal femoral angle (LDFA) were expressed as the deviation from the perpendicular line to the mechanical axes, and the mechanical HKA (mHKA) was defined as the angle between the femoral and tibial mechanical axes. Using the MPTA and LDFA, the arithmetic HKA (aHKA; MPTA + LDFA) and the joint line obliquity (JLO; MPTA − LDFA) were calculated, and the preoperative and postoperative values were compared.

Results

The preoperative aHKA and the postoperative mHKA values were similar (−0.38° ± 2.96°) and significantly smaller than the difference between the preoperative and postoperative mHKAs (4.58° ± 3.60°, P < 0.05). Meanwhile, the MPTA tended to be varus, and the LDFA tended to be valgus. Eventually, the JLO inclined more medially from −6.33° ± 3.42° preoperatively to −8.97° ± 3.92° postoperatively, representing a significant difference (P < 0.05).

Conclusion

The preoperative aHKA was similar to the postoperative mHKA. Therefore, it can be regarded as a predictor of postoperative leg alignment after Oxford UKA. Meanwhile, there was a medial incline of the joint line. Further investigation is required to evaluate the effect of such a joint line alteration.

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