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Small change in the arithmetic hip-knee-ankle angle during unicompartmental knee arthroplasty improves early postoperative functional outcomes

  • Knee Arthroplasty
  • Published:
Archives of Orthopaedic and Trauma Surgery Aims and scope Submit manuscript

Abstract

Introduction

The optimal lower-limb alignment after unicompartmental knee arthroplasty (UKA) remains controversial. This study aimed to investigate the optimal lower-limb alignment for functional improvement in the early post-UKA period. We hypothesized that a small change (Δ) in the arithmetic hip-knee-ankle (aHKA) angle during surgery would result in better postoperative knee function.

Materials and methods

This single-centered, retrospective study analyzed 91 patients (91 knees) who underwent UKA from April 2021 and December 2022. Preoperative and postoperative standing whole-leg radiographs were used to evaluate the mechanical HKA angle and aHKA angle. The aHKA angle was calculated from the medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA). We defined restored aHKA angle as a postoperative aHKA angle within ± 3° of the preoperative aHKA angle. Functional improvement was evaluated using the preoperative and one-year postoperative Knee Society Scoring 2011 (KSS 2011). A multivariate regression analysis was performed to investigate the optimal lower-limb alignment for functional improvement.

Result

Postoperative restored aHKA angle (p = 0.020) was the only significant factor for improved KSS 2011 scores. Postoperative restored aHKA angle was obtained in 64 patients (70%). ΔMPTA (p < 0.001) and ΔLDFA (p = 0.037) were significant factors associated with a postoperative restored aHKA angle.

Conclusions

UKA restores the native knee, including resurfacing constitutional alignment and medial collateral ligament tension. Minimal change in the aHKA angle during UKA improves the functional outcomes of the knee during the early postoperative period, consistent with the minimally invasive surgical concept of UKA.

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Data availability

The data that support the findings of this study are available from the corresponding author, upon reasonable request.

Code Availability

Not applicable.

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Acknowledgements

We thank Hidetoshi Tsushima and Junki Adachi (Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan) for data collection and their invaluable advice for this study.

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No funds, grants, or other support was received..

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Authors and Affiliations

  1. Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan

    Yasuhiko Kokubu, Shinya Kawahara, Satoshi Hamai, Yukio Akasaki, Taishi Sato & Yasuharu Nakashima

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  1. Yasuhiko Kokubu
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  2. Shinya Kawahara
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  3. Satoshi Hamai
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  4. Yukio Akasaki
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Contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Yasuhiko Kokubu, Shinya Kawahara, Yukio Akasaki, Satoshi Hamai, and Taishi Sato. The first draft of the manuscript was written by Yasuhiko Kokubu and Shinya Kawahara. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Shinya Kawahara.

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Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study was approved by the local Institutional Review Board (No. 2020–204).

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Informed consent was obtained from all individual participants included in the study.

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Kokubu, Y., Kawahara, S., Hamai, S. et al. Small change in the arithmetic hip-knee-ankle angle during unicompartmental knee arthroplasty improves early postoperative functional outcomes. Arch Orthop Trauma Surg (2024). https://doi.org/10.1007/s00402-024-05309-2

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