Reflex Contributions to Joint Stability

描述（由申请人提供）：为了探索关节神经支配对关节稳定性的潜在贡献，我们建议研究关节传入神经在促进人体膝关节中外侧稳定性中的作用，并试图在良好控制的环境中表征关节传入神经反射的输入-输出特性。选择膝内翻/外翻（v/v）作为模型是有利的，因为肌肉本体感受器在这些方向上促进反射激活的可能性较小，允许更直接地检查韧带/包膜机械感受器作用的输入/输出特性。根据我们的初步研究，拉伸关节韧带的机械扰动在穿过膝关节的肌肉中产生反射反应，并且这些反射是有组织的，以便选择性地补偿外翻负荷。因此，我们假设关节传入介导的肌肉激活可以通过对人体膝盖施加机械v/v载荷而引起，并且反射强度将是角扰动大小的增加函数。我们还提出内侧肌肉对外侧扰动会表现出更大的反射反应，而外侧肌肉对内侧扰动会表现出更大的反应。这种反射反应将显著增加膝关节在v/v方向上的僵硬度。最后，我们假设这些基于反射的激活模式的空间分布最大化了膝关节外翻（或内翻）负荷的阻力。定量测量膝关节肌肉的关节周围介导反射激活将确定72名受试者。一个斜外翻位置扰动将通过一个伺服马达应用于受试者的膝盖。[负荷条件将通过使用线性伺服电机系统在位置扰动期间向脚底施加轴向力来模拟。轴向力将用于增加关节压力，并将以受试者体重的百分比表示。将记录并分析膝关节主要肌肉的扭矩和肌电活动。为了定量地检查反射作用的机制，将基于10名受试者的完整膝关节mri构建三维受试者特异性髌骨-股骨和胫骨-股骨关节模型。在模型中，每个肌肉激活将被表示为一个分布函数，其均值和标准差以Aim 1中从同一受试者获得的反射激活模式为界。我们将使用蒙特卡罗模拟该模型来获得随机四头肌激活模式的可能分布的估计，这些模式可以响应于施加的外翻载荷而产生内翻力矩。然后将这些基于模型的内翻力矩与使用实验肌肉激活时模型计算的内翻力矩进行比较（数据来自Aim 1）。准静态和动态反射刚度将分别使用斜坡和伪随机二进制v/v位置扰动应用于9名受试者的膝盖进行量化。使用延迟线性模型估计关节刚度和阻尼系数。在静态神经和机械状态下获得的基于机械感受器的膝关节反射的输入/输出特性的识别将为未来的研究奠定坚实的基础，这些研究将研究功能性任务中关节传入事件的贡献。我们认为，膝关节关节周围组织中的拉伸受体在促进关节内外侧稳定性方面起着重要作用，这将潜在地对训练如何提高整体关节稳定性产生重大影响。

DESCRIPTION (provided by applicant): To explore the potential contributions of joint innervation towards joint stability, we propose to study the role of joint afferents in promoting medio-lateral stability of the human knee joint and seek to characterize the input-output properties of joint afferents-based reflexes in a well-controlled environment. The choice of knee varus/valgus (v/v) as a model is advantageous because there is less likelihood that muscle proprioceptors will contribute to reflex activation in these directions, allowing more straight-forward examination of input/output properties of ligament/capsular mechanoreceptor effects. Based on our preliminary studies, mechanical perturbations that stretch joint ligaments produced reflex response in muscles traversing the knee joint, and that these reflexes were organized so as to compensate selectively for varus-valgus loading. Accordingly, we hypothesize that joint afferents mediated muscle activation can be elicited by the application of mechanical v/v loading to the human knee, and that the reflex intensity will be an increasing function of the angular perturbation size. We also propose that medial muscles will show a larger reflex response to lateral perturbation, and lateral muscles will show a larger response to medial perturbations. This reflex response will significantly increase knee joint stiffness in the v/v direction. Finally, we hypothesize that spatial distribution of these reflex-based activation patterns maximize resistance to the valgus (or varus) loading at the knee. Quantitative measures of periarticular mediated reflex activation of knee muscles will be determined in 72 subjects. A ramp valgus positional perturbation will be applied at the subject knee via a servomotor. [Load bearing conditions will be simulated by the application of an axial force to the sole of the foot during positional perturbation using a linear servomotor system. The axial force will be used to increase joint compression, and will be represented as a percent of the subject s body weight.] Torque and EMG activity will be recorded and analyzed in major knee muscles. To examine the mechanics of reflex action quantitatively, a three-dimensional subject-specific patello-femoral and tibio-femoral joint model will be constructed based on complete knee MRIs of a subset of 10 subjects. In the model, each muscle activation will be represented as a distribution function with a mean and standard deviation bounded by the reflex activation patterns obtained from the same subject in Aim 1. We will use Monte Carlo simulations with this model to obtain estimates of the likely distribution of random quadriceps activation patterns that can generate varus moment in response to an applied valgus load. These model-based varus moments are then compared to the varus moment computed by the model when experimental muscle activations are used (data from Aim 1). A quasistatic and dynamic reflex stiffness will be quantified using ramp and pseudo-random binary v/v positional perturbation applied to the knee in 9 subjects, respectively. Joint stiffness and damping coefficients will be estimated using delayed linear models. Identification of the input/output properties of the mechanoreceptor-based knee joint reflexes obtained under static neurological and mechanical states will serve as solid basis for future studies, which will investigate joint afferents contributions during a functional task. We believe that stretch receptors in periarticular tissues of the knee joint play a major role in promoting joint medial-lateral stability, which will potentially have a major impact on how training may improve overall joint stability.