下肢の冠状アライメントの測定精度に及ぼす矢状面と軸方向の膝関節の回転の影響

The effect of knee joint rotation in the sagittal and axial plane on the measurement accuracy of coronal alignment of the lower limb.

• Hyun-Soo Moon
• Chong-Hyuk Choi
• Min Jung
• Dae-Young Lee
• Jung-Hwan Kim
• Sung-Hwan Kim

抄録

背景:

従来の全長体重載荷前後（FLWAP）X線写真における下肢の冠状アライメントの測定には膝関節の回転の影響があることが報告されていたが，実際の体重載荷状況を考慮しつつ，3次元画像を用いて矢状面と軸方向面での膝関節回転の影響を同時に考慮した比較解析は行われていなかった．本研究の目的は、FLWAPラジオグラフにおける下肢の冠状アライメントの測定精度に及ぼす膝関節回転の影響を検討することであった。

BACKGROUND: Although the measurement of coronal alignment of the lower limb on conventional full-length weight-bearing anteroposterior (FLWAP) radiographs was reported to be influenced by the knee joint rotation, no comparative analysis was performed considering the effects of knee joint rotation on the sagittal and axial planes simultaneously using the three-dimensional images while taking into account the actual weight-bearing conditions. The aim of this study was to investigate the effect of knee joint rotation on the measurement accuracy of coronal alignment of the lower limb on the FLWAP radiograph.

方法:

FLWAPとEOS画像の両方を撮影した連続した90人の患者（180人の下肢）のX線画像をレトロスペクティブにレビューした。FLWAP画像とEOS画像の機械的脛骨大腿角（mTFA）のデルタ値（ΔmTFA）、EOS画像の膝屈伸角（矢状面回転）、FLWAP画像の膝蓋骨回転（軸面回転）の関係を解析した。さらに、膝関節の回転方向ごとにサブグループ解析を行った。

METHODS: Radiographic images of 90 consecutive patients (180 lower limbs) who took both the FLWAP radiograph and the EOS image were retrospectively reviewed. The relationship among delta values of mechanical tibiofemoral angle (mTFA) between the FLWAP radiographs and the EOS images (ΔmTFA), knee flexion/extension angle (sagittal plane rotation) on the EOS images, and patellar rotation (axial plane rotation) on the FLWAP radiographs were analyzed. Further, subgroup analysis according to each direction of knee joint rotation was performed.

結果:

ΔmTFAと矢状面回転との間には有意な相関が認められた(r=0.368, P<0.001)が、軸方向の面回転は相関しなかった。方向別の解析では、膝屈曲群のみに統計的に有意な相関が認められた(r=0.399, P<0.001)。回帰分析では、ΔmTFAと矢状面回転との間に有意な線形関係が認められた（r=0.136、P<0.001）。膝蓋骨回転数が3%以上の患者を対象とした追加のサブグループ分析では、ΔmTFAと矢状面回転数との間に線形関係があるという同様の結果が得られた(r=0.257, P<0.001)が、膝蓋骨回転数が3%未満の患者では統計的に有意な関係は認められなかった。

RESULTS: There was a significant correlation between ΔmTFA and sagittal plane rotation (r = 0.368, P <  0.001), whereas axial plane rotation was not correlated. In the analysis according to the direction, statistically significant correlation was observed only in the knee flexion group (r = 0.399, P <  0.001). The regression analysis showed a significant linear relationship between ΔmTFA and sagittal plane rotation (r = 0.136, P <  0.001). Additional subgroup analysis in patients with the patellar rotation greater than 3% showed a similar result of a linear relationship between ΔmTFA and sagittal plane rotation (r = 0.257, P <  0.001), whereas no statistically significant relationship was found in patients with the patellar rotation less than 3%.

結論:

FLWAPラジオグラフ上での下肢のコロナアライメントの測定精度は、膝の屈曲、特に軸方向平面内での膝関節の微妙な回転がある場合に影響を受けると考えられます。膝の軸面回転を伴わない厳密な膝蓋骨前方位置であれば、膝の屈曲拘縮が固定されていても正確な測定結果が得られる可能性がある。

CONCLUSION: The measurement accuracy of coronal alignment of the lower limb on the FLWAP radiographs would be influenced by knee flexion, specifically when there is any subtle rotation of the knee joint in the axial plane. A strict patellar forward position without axial plane rotation of the knee could provide accurate results of the measurement even if there is a fixed flexion contracture of the knee.