Department of Biomedical Engineering, University of Minnesota, Twin Cities, Minneapolis, MN 55455.
Divisions of Physical Therapy and Rehabilitation Science, Department of Rehabilitation Medicine, University of Minnesota, Twin Cities, Minneapolis, MN 55455.
J Biomech Eng. 2022 Jun 1;144(6). doi: 10.1115/1.4053993.
The lumbar facet capsular ligament, which surrounds and limits the motion of each facet joint in the lumbar spine, has been recognized as being mechanically significant and has been the subject of multiple mechanical characterization studies in the past. Those studies, however, were performed on isolated tissue samples and thus could not assess the mechanical state of the ligament in vivo, where the constraints of attachment to rigid bone and the force of the joint pressure lead to nonzero strain even when the spine is not loaded. In this work, we quantified these two effects using cadaveric lumbar spines (five spines, 20 total facet joints harvested from L2 to L5). The effect of joint pressure was measured by injecting saline into the joint space and tracking the 3D capsule surface motion via digital image correlation, and the prestrain due to attachment was measured by dissecting a large section of the tissue from the bone and by tracking the motion between the on-bone and free states. We measured joint pressures of roughly 15-40 kPa and local first principal strains of up to 25-50% when 0.3 mL of saline was injected into the joint space; the subsequent increase in pressure and strain were more modest for further increases in injection volume, possibly due to leakage of fluid from the joint. The largest stretches were in the bone-to-bone direction in the portions of the ligament spanning the joint space. When the ligament was released from the vertebrae, it shrank by an average of 4-5%, with local maximum (negative) principal strain values of up to 30%, on average. Based on these measurements and previous tests on isolated lumbar facet capsular ligaments, we conclude that the normal in vivo state of the facet capsular ligament is in tension, and that the collagen in the ligament is likely uncrimped even when the spine is not loaded.
腰椎小关节囊韧带环绕并限制腰椎小关节的运动，其力学作用显著，过去有多项针对其力学特性的研究。然而，这些研究都是在离体组织样本上进行的，因此无法评估韧带在体内的力学状态，在体内，韧带与刚性骨骼的连接约束和关节压力的力会导致即使在脊柱未受力时也会产生非零应变。在这项工作中，我们使用尸体腰椎（5 个脊柱，从 L2 到 L5 共采集 20 个小关节）来量化这两种效应。关节压力的影响通过向关节间隙注入生理盐水并通过数字图像相关来跟踪 3D 囊表面运动来测量，而由于附着产生的预应变通过从骨骼上解剖出一大块组织并跟踪在骨上和自由状态之间的运动来测量。当向关节间隙注入 0.3 毫升生理盐水时，我们测量到关节压力约为 15-40 kPa，局部第一主应变高达 25-50%；进一步增加注射量会导致压力和应变的增加更为适度，这可能是由于关节内的液体泄漏。在跨越关节间隙的韧带的骨-骨部分，伸展量最大。当韧带从椎骨上释放时，它平均收缩 4-5%，局部最大（负）主应变值高达 30%，平均而言。基于这些测量值和以前对离体腰椎小关节囊韧带的测试，我们得出结论，小关节囊韧带的正常体内状态是张紧的，即使在脊柱未受力时，韧带中的胶原也可能未卷曲。
