人工膝関節全置換術後の下肢アライメント変化が脚長に及ぼす影響

抄録

Objective: The purpose of this study was to investigate the change of whole leg length after total knee arthroplasty (TKA) and its correlated factors.

Methods: A total of 37 knees (8 men and 29 women) with a mean age of 78±5.8 years (range: 66-86 years) who underwent primary TKA, were enrolled in the present study. We obtained radiographs of the lower limbs in their entirety in a standing position before and three weeks after their TKA. We measured the mechanical axis (MA) length, mechanical axis deviation (MAD) at the knee joint, hip-knee-ankle (HKA) angle, and knee flexion (KF) angle.

A paired t-test was used to evaluate changes of each parameter after TKA. We also performed univariate and multivariate analyses to evaluate factors which correlated with the change in MA length. The threshold for significance was a P value of<0.05.

Results: Every measured parameter except for MA length changed after TKA. Preoperatively, MAD 43.7±21.1%, HKA angle−8.2±8.0°, KF angle 14.7±7.3°; Post operatively, MAD 9.1±7.4%, HKA angle−0.7±2.8°, KF angle 11.6±7.3°; P<0.05. In univariate analyses, the postoperative change in MA length significantly correlated with the change in MAD (R=−0.58, P<0.001) and KF angle (R=−0.39, P=0.02). In the multivariate analysis, the change in MAD was the only factor which correlated with the change in MA length (R²=0.40, P<0.001).

Conclusion: MAD which is an indicator of the coronal lower limb alignment, influences the MA length. Therefore, we may consider the leg length change when performing TKA and bring the lower limb into neutral alignment in patients with severe varus or valgus deformity.