Thornton Gail M, Schwab Timothy D, Oxland Thomas R
McCaig Centre for Joint Injury and Arthritis Research, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada.
Clin Biomech (Bristol). 2007 Oct;22(8):932-40. doi: 10.1016/j.clinbiomech.2007.05.004. Epub 2007 Jun 28.
Ligaments may be subjected to higher than normal loads when one of the complementary ligament restraints of a joint or the ligament itself is injured. Damage can accumulate in a ligament due to cyclic and static loading under these increased loads, but it remains unknown whether one type of loading will cause rupture faster than the other in medial collateral ligament.
The objective of this study was to compare the time and strain behaviour of normal rabbit medial collateral ligaments under static and cyclic loading over a wide range of applied stresses, with particular emphasis on time-to-rupture. Stresses were normalized to ultimate tensile strength and selected from three regions of the stress-strain curve: two linear-region stresses (60% and 30% of the ultimate tensile strength) and one stress at the transition from the toe-region to the linear-region (15% of the ultimate tensile strength).
Cyclic loading caused faster rupture than static loading at all stresses. Strain-time profiles were different in that the increase in strain (strain relative to initial strain) was greater under static than cyclic loading prior to rupture. However, steady-state strain rate (when increase in strain reaches a plateau in the secondary strain stage) was greater under cyclic than static loading.
These results suggest that cyclic loading is more detrimental than static loading in ligaments that are subjected to higher than normal stresses following injury of a complementary restraint or the ligament itself.
当关节的互补韧带约束之一或韧带本身受损时，韧带可能会承受高于正常的负荷。在这些增加的负荷下，由于循环和静态负荷，韧带中的损伤会累积，但内侧副韧带中一种负荷类型是否会比另一种负荷类型更快地导致破裂仍不清楚。
本研究的目的是比较正常兔内侧副韧带在广泛的施加应力下，在静态和循环负荷下的时间和应变行为，特别强调破裂时间。应力被归一化为极限拉伸强度，并从应力-应变曲线的三个区域中选择：两个线性区域应力（极限拉伸强度的60%和30%）和一个从趾部区域到线性区域过渡处的应力（极限拉伸强度的15%）。
在所有应力下，循环负荷比静态负荷导致更快的破裂。应变-时间曲线不同，因为在破裂前，静态负荷下的应变增加（相对于初始应变的应变）大于循环负荷下的应变增加。然而，循环负荷下的稳态应变率（当应变增加在二次应变阶段达到平台期时）大于静态负荷下的稳态应变率。
这些结果表明，在互补约束或韧带本身受损后承受高于正常应力的韧带中，循环负荷比静态负荷更具危害性。
