Rodriguez Marcel Leonardo, Li LePing
Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Drive, N.W, Calgary, AB, T2N 1N4, Canada.
BMC Musculoskelet Disord. 2017 Nov 14;18(1):447. doi: 10.1186/s12891-017-1805-9.
The knee joint performs mechanical functions with various loading and unloading processes. Past studies have focused on the kinematics and elastic response of the joint with less understanding of the rate-dependent load response associated with viscoelastic and poromechanical behaviors.
Forty-five fresh porcine knee joints were used in the present study to determine the loading-rate-dependent force-compression relationship, creep and relaxation of normal, dehydrated and meniscectomized joints.
The mechanical tests of all normal intact joints showed similar strong compression-rate-dependent behavior: for a given compression-magnitude up to 1.2 mm, the reaction force varied 6 times over compression rates. While the static response was essentially linear, the nonlinear behavior was boosted with the increased compression rate to approach the asymptote or limit at approximately 2 mm/s. On the other hand, the joint stiffness varied approximately 3 times over different joints, when accounting for the maturity and breed of the animals. Both a loss of joint hydration and a total meniscectomy greatly compromised the load support in the joint, resulting in a reduction of load support as much as 60% from the corresponding intact joint. However, the former only weakened the transient load support, but the latter also greatly weakened the equilibrium load support. A total meniscectomy did not diminish the compression-rate-dependence of the joint though.
These findings are consistent with the fluid-pressurization loading mechanism, which may have a significant implication in the joint mechanical function and cartilage mechanobiology.
膝关节在各种加载和卸载过程中执行机械功能。过去的研究主要集中在关节的运动学和弹性反应，而对与粘弹性和孔隙力学行为相关的速率依赖性负荷反应了解较少。
本研究使用45个新鲜猪膝关节来确定正常、脱水和半月板切除关节的负荷率依赖性力-压缩关系、蠕变和松弛情况。
所有正常完整关节的力学测试均显示出类似的强烈压缩率依赖性行为：对于高达1.2毫米的给定压缩幅度，反作用力在压缩率范围内变化6倍。虽然静态反应基本呈线性，但随着压缩率增加，非线性行为增强，在约2毫米/秒时接近渐近线或极限。另一方面，考虑到动物的成熟度和品种，不同关节的关节刚度变化约3倍。关节脱水和完全半月板切除均极大地损害了关节的负荷支撑能力，导致负荷支撑能力比相应的完整关节减少多达60%。然而，前者仅削弱了瞬态负荷支撑，而后者也极大地削弱了平衡负荷支撑。不过，完全半月板切除并未减弱关节的压缩率依赖性。
这些发现与流体加压加载机制一致，这可能对关节机械功能和软骨力学生物学具有重要意义。
