Background: 

Torsion of the lower extremities has been suggested to be a predisposing factor for patellar instability. However, no clear torsional factors have been clarified. This study aimed to elucidate the rotational geometry of the lower limb through segmental analysis in patients with patellar instability.

Methods: 

Eighty-three patients with patellar instability were included. Computed tomography of the lower limb was acquired. Femoral and tibial torsion were measured in different segments. Femoral and tibial torsion in each segment was compared between the high- and normal-torsion groups to investigate which segment contributes the most.

Results: 

All segments of femoral and tibial torsion except proximal femoral torsion showed significant differences between the high- and normal-torsion groups. The average proximal femoral torsion was 1.9° ± 7.1°, indicating that there was only slight torsion in the segment of the femoral neck. The angle between the femoral neck and the foot orientation in the normal-torsion, high-torsion tibial, and combined high-torsion femoral and tibial groups was 89.1° ± 12.0°, 81.3° ± 9.4°, and 98.2° ± 11.7°, respectively (p < 0.001), which suggested that the femoral neck remained nearly perpendicular to the foot orientation in the normal-torsion group. Shaft and distal femoral torsion contributed the most to total femoral torsion. For tibial torsion, from distal to proximal, internal torsion of both the proximal and distal segments contributed to the high torsion. There was no significant difference between distal femoral torsion and proximal tibial torsion, which suggested that, rather than the distal femur rotating internally on its own, the distal femur and the proximal tibia simultaneously rotated internally.

Conclusions: 

In patients with patellar instability, torsional deformity occurs along the length of the tibia and in the shaft and distal segments of the femur. The comprehensive embodiment of lower-extremity malrotation is an internal rotation deformity of the knee.

Clinical Relevance: 

This study elucidated the rotational geometry of the lower limb through a detailed segmental analysis in patients with patellar instability. It could serve as a theoretical basis for choosing a derotational osteotomy site and may be a reference for additional clinical research.

中文翻译：

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膝关节内扭转：髌骨不稳患者下肢旋转不良的一种表现

背景： 

下肢扭转被认为是髌骨不稳定的诱发因素。然而，没有明确的扭转因素。本研究旨在通过对髌骨不稳定患者的节段分析来阐明下肢的旋转几何形状。

方法： 

包括 83 名髌骨不稳定患者。获得了下肢的计算机断层扫描。在不同节段测量股骨和胫骨扭转。在高扭转组和正常扭转组之间比较每个节段的股骨和胫骨扭转，以研究哪个节段贡献最大。

结果： 

除股骨近端扭转外，所有股骨和胫骨扭转节段在高扭转组和正常扭转组之间均显示出显着差异。股骨近端平均扭转为1.9°±7.1°，表明股骨颈段仅有轻微扭转。正常扭转组、高扭转胫骨组和高扭转股胫联合组股骨颈与足部方向的夹角分别为89.1°±12.0°、81.3°±9.4°和98.2°±11.7°，分别（p < 0.001），这表明在正常扭转组中股骨颈保持几乎垂直于足部方向。股骨干和股骨远端扭转对总股骨扭转的贡献最大。对于胫骨扭转，从远端到近端，近端和远端节段的内扭转都导致了高扭转。

结论： 

在髌骨不稳定的患者中，扭转畸形发生在胫骨的长度以及股骨的干和远端部分。下肢旋转不良的综合表现是膝关节内旋畸形。

临床相关性： 

本研究通过对髌骨不稳定患者的详细节段分析，阐明了下肢的旋转几何形状。它可以作为选择去旋截骨部位的理论依据，并可能为进一步的临床研究提供参考。