Han Seong-Won, Sawatsky Andrew, Jinha Azim, Herzog Walter
University of Calgary.
Federal University of Santa Catarina.
J Appl Biomech. 2020 Aug 25;36(6):390-396. doi: 10.1123/jab.2020-0056. Print 2020 Dec 1.
Vastus medialis (VM) weakness is thought to alter patellar tracking, thereby changing the loading of the patellofemoral joint (PFJ), resulting in patellofemoral pain. However, it is challenging to measure VM force and weakness in human studies, nor is it possible to measure the associated mechanical changes in the PFJ. To obtain fundamental insight into VM weakness and its effects on PFJ mechanics, the authors determined PFJ loading in the presence of experimentally simulated VM weakness. Skeletally mature New Zealand White rabbits were used (n = 6), and the vastus lateralis, VM, and rectus femoris were stimulated individually through 3 custom-built nerve cuff electrodes. Muscle torque and PFJ pressure distribution were measured while activating all muscles simultaneously, or when the vastus lateralis and rectus femoris were activated, while VM was not, to simulate a quadriceps muscle strength imbalance. For a given muscular joint torque, peak pressures were greater and joint contact areas were smaller when simulating VM weakness compared with the condition where all muscles were activated simultaneously. The results in the rabbit model support that VM weakness results in altered PFJ loading, which may cause patellofemoral pain, often associated with a strength imbalance of the knee extensor muscle group.
股内侧肌（VM）无力被认为会改变髌骨轨迹，从而改变髌股关节（PFJ）的负荷，导致髌股疼痛。然而，在人体研究中测量VM力量和无力具有挑战性，而且也无法测量PFJ相关的力学变化。为了深入了解VM无力及其对PFJ力学的影响，作者在实验模拟VM无力的情况下测定了PFJ负荷。使用了骨骼成熟的新西兰白兔（n = 6），通过3个定制的神经袖套电极分别刺激股外侧肌、VM和股直肌。在同时激活所有肌肉时，或在激活股外侧肌和股直肌而不激活VM以模拟股四头肌力量失衡时，测量肌肉扭矩和PFJ压力分布。对于给定的肌肉关节扭矩，与同时激活所有肌肉的情况相比，模拟VM无力时峰值压力更大，关节接触面积更小。兔模型的结果支持VM无力会导致PFJ负荷改变，这可能会引起髌股疼痛，而髌股疼痛通常与膝伸肌群的力量失衡有关。
