Background

Lower limb malrotations can be observed in long leg radiographs, affecting the measurement of the angle between the mechanical and anatomical axes. The purposes were to analyze the effect of limb rotation and to evaluate the accuracy of the corrected angle between the mechanical and anatomical axes based on the patellar ML position.

Hypothesis

The hypothesis was that the correction of the angle between the mechanical and anatomical axes according to the patellar ML position can reduce the error from the angle in the true AP view in most of the knees.

Patients and methods

A total of 100 consecutive knees with varus deformity undergoing primary total knee arthroplasty were included. Computed tomography images were digitally reconstructed in the neutral position, and internally and externally rotated at 10° and 20°, respectively. The patellar ML position relative to the medial (0%) and lateral (100%) epicondyles and the angle between the mechanical and anatomical axes of the femur were measured. The corrected angle between the mechanical and anatomical axes was calculated using the averaged translational ratio.

Results

In the neutral position, the patellar center position was 56.1% (standard deviation [SD] = 4.7%), which was 31.4% (SD = 7.2%) and 80.2% (SD = 5.4%) in the 20° internal and external rotation, respectively. The angle between the mechanical and anatomical axes was 2.6° (SD = 2.0°) and 8.1° (SD = 2.1°) in the 20° internal and external rotation, respectively. On average, if the patellar center shifted 10%, the change of the angle between the mechanical and anatomical axes of the femur was 1.13°. Applying the corrected angle, a discrepancy from the neutral position decreased.

Conclusion

The method to correct the angle between the mechanical and anatomical axes according to the patellar ML position can be used to reduce the measurement error for preoperative planning using a long leg radiograph.

Level of evidence

III.

中文翻译：

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髌骨内外位可用于纠正膝内翻全膝关节置换术中腿部旋转对术前计划的影响

背景

在长腿X光片中可以观察到下肢旋转不良，影响机械轴和解剖轴之间角度的测量。目的是分析肢体旋转的效果并评估基于髌骨 ML 位置的机械轴和解剖轴之间校正角度的准确性。

假设

假设根据髌骨 ML 位置校正机械轴和解剖轴之间的角度可以减少大多数膝盖与真实 AP 视图中的角度的误差。

患者和方法

总共包括 100 个连续膝关节内翻畸形且接受初次全膝关节置换术的患者。计算机断层扫描图像在中立位置进行数字重建，并分别内部和外部旋转 10° 和 20°。测量髌骨 ML 相对于内上髁 (0%) 和外上髁 (100%) 的位置以及股骨机械轴和解剖轴之间的角度。使用平均平移比计算机械轴和解剖轴之间的校正角度。

结果

中立位时，髌骨中心位置为56.1%（标准差[SD]  =  4.7%），20°内、外旋时为31.4%（SD  =  7.2%）、80.2%（SD  = 5.4%）  ， 分别。20° 内旋和外旋时，机械轴和解剖轴之间的角度分别为 2.6° (SD  =  2.0°) 和 8.1° (SD  = 2.1°)。 平均而言，如果髌骨中心移动10%，股骨机械轴和解剖轴之间的角度变化为1.13°。应用校正后的角度，与中性位置的差异减小。

结论

根据髌骨ML位置校正机械轴和解剖轴之间的角度的方法可用于减少使用长腿X光片进行术前计划的测量误差。

证据级别

三．