Fottner Andreas, Woiczinski Matthias, Kistler Manuel, Schröder Christian, Schmidutz Tobias F, Jansson Volkmar, Schmidutz Florian
Department of Orthopedic Surgery, Physical Medicine and Rehabilitation, University Hospital of Munich (LMU), Campus Grosshadern, Marchioninistraße 15, Munich 81377, Germany.
Laboratory for Biomechanics and Experimental Orthopedics, Grosshadern Medical Center, University of Munich (LMU), Germany.
Clin Biomech (Bristol). 2018 Oct;58:14-20. doi: 10.1016/j.clinbiomech.2018.07.006. Epub 2018 Jul 5.
Varus position of cementless stems is a common malalignment in total hip arthroplasty. Clinical studies have reported a low rate of aseptic loosening but an increased risk for thigh pain. This in vitro study aimed to evaluate these clinical observations from a biomechanical perspective.
A conventional cementless stem (CLS Spotorno) was implanted in a regular, straight (size 13.75) as well as in a varus position (size 11.25) in 6 composite femora (Sawbones), respectively. Primary stability was assessed by recording 3-dimensional micromotions under dynamic load bearing conditions and stress shielding was evaluated by registering the surface strain before and after stem insertion.
Primary stability for stems in varus malposition revealed significantly lower micromotions (p < 0.05) for most regions compared to stems in neutral position. The greatest difference was observed at the tip of the stem where the straight aligned implants exceeded the critical upper limit for osseous integration of 150 μm. The surface strains for the varus aligned stems revealed a higher load transmission to the femur, resulting in a clearly altered strain distribution.
This biomechanical study confirms the clinical findings of a good primary stability of cementless stems in a varus malposition, but impressively demonstrates the altered load transmission with the risk for postoperative thigh pain.
在全髋关节置换术中，非骨水泥型股骨柄内翻位是一种常见的对线不良情况。临床研究报告称其无菌性松动率较低，但大腿疼痛风险增加。本体外研究旨在从生物力学角度评估这些临床观察结果。
将一个传统的非骨水泥型股骨柄（CLS Spotorno）分别以正常、笔直（尺寸13.75）以及内翻位（尺寸11.25）植入6个复合股骨（Sawbones）中。通过记录动态承重条件下的三维微动来评估初始稳定性，并通过记录股骨柄植入前后的表面应变来评估应力遮挡。
与处于中立位的股骨柄相比，内翻错位的股骨柄在大多数区域的初始稳定性显示出明显更低的微动（p < 0.05）。在股骨柄尖端观察到最大差异，笔直对齐的植入物超过了骨整合的临界上限150μm。内翻对齐的股骨柄的表面应变显示出更高的载荷传递至股骨，导致应变分布明显改变。
这项生物力学研究证实了临床研究结果，即非骨水泥型股骨柄在内翻错位时具有良好的初始稳定性，但令人印象深刻地证明了载荷传递的改变以及术后大腿疼痛的风险。
