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Introduction <p>The amount of change in coronal alignment by unicompartmental knee arthroplasty (UKA) is important when considering its long-term results. This study investigated whether the amount of change in mechanical hip-knee-ankle (mHKA) angle by medial fixed-bearing UKA can be predicted based on the arithmetic hip-knee-ankle (aHKA) angle, an indicator of bony nature that is independent of soft tissue balance.</p> Materials and methods <p>The research involved 101 patients (125 knees) who underwent medial fixed-bearing UKA with the spacer-block technique. Pre- and postoperative mHKA angles, aHKA angle (180°– lateral distal femoral angle + medial proximal tibial angle), insert thickness, and the amount of bone cuts were measured. The component gap in extension was measured using a UKA tensor, and the pre-osteotomy gap was calculated. The correlation between aHKA angle minus preoperative mHKA angle and changes in mHKA angle, as well as the pre-osteotomy gap, were analysed. Additionally, changes in mHKA angle and total osteotomy volume were compared based on insert thickness.</p> Results <p>A positive correlation was found between aHKA angle minus preoperative mHKA angle and the change in mHKA angle. The pre-osteotomy gap was also positively correlated with aHKA angle minus preoperative HKA angle. Greater changes in mHKA angle occurred in cases with inserts ≥ 9&#xa0;mm compared to 8&#xa0;mm inserts, though osteotomy volume did not significantly differ between the groups.</p> Conclusions <p>In fixed-bearing UKA, postoperative changes in mHKA angle are likely to be more pronounced when there is a significant difference between aHKA angle and preoperative mHKA angle. Surgical planning should account for this factor to optimise outcomes.</p>

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Amount of mechanical hip-knee-ankle (mHKA) angle correction by fixed-bearing medial UKA can be predicted using a new morphological assessment method: the arithmetic hip-knee-ankle (aHKA) angle

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  • 发表日期：

    2025年4月26日

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  • Naoki Nakano,
  • Masanori Tsubosaka,
  • Tomoyuki Kamenaga,
  • Yuichi Kuroda,
  • Kazunari Ishida,
  • Shinya Hayashi,
  • Ryosuke Kuroda,
  • Tomoyuki Matsumoto

摘要

Introduction

The amount of change in coronal alignment by unicompartmental knee arthroplasty (UKA) is important when considering its long-term results. This study investigated whether the amount of change in mechanical hip-knee-ankle (mHKA) angle by medial fixed-bearing UKA can be predicted based on the arithmetic hip-knee-ankle (aHKA) angle, an indicator of bony nature that is independent of soft tissue balance.

Materials and methods

The research involved 101 patients (125 knees) who underwent medial fixed-bearing UKA with the spacer-block technique. Pre- and postoperative mHKA angles, aHKA angle (180°– lateral distal femoral angle + medial proximal tibial angle), insert thickness, and the amount of bone cuts were measured. The component gap in extension was measured using a UKA tensor, and the pre-osteotomy gap was calculated. The correlation between aHKA angle minus preoperative mHKA angle and changes in mHKA angle, as well as the pre-osteotomy gap, were analysed. Additionally, changes in mHKA angle and total osteotomy volume were compared based on insert thickness.

Results

A positive correlation was found between aHKA angle minus preoperative mHKA angle and the change in mHKA angle. The pre-osteotomy gap was also positively correlated with aHKA angle minus preoperative HKA angle. Greater changes in mHKA angle occurred in cases with inserts ≥ 9 mm compared to 8 mm inserts, though osteotomy volume did not significantly differ between the groups.

Conclusions

In fixed-bearing UKA, postoperative changes in mHKA angle are likely to be more pronounced when there is a significant difference between aHKA angle and preoperative mHKA angle. Surgical planning should account for this factor to optimise outcomes.