Nakama Leena H, King Karen B, Abrahamsson Sven, Rempel David M
University of California, Berkeley, CA, USA.
J Orthop Res. 2007 Sep;25(9):1176-84. doi: 10.1002/jor.20408.
We reported previously the formation of microtears in an in vivo loaded Flexor Digitorum Profundus (FDP) rabbit tendon with a repetition rate of 60 repetitions per minute and a peak force of 15% of maximum peak tetanic force for 80 cumulative hours. Tear area as a percent of tendon area, tear density (tears/mm(2)), and mean tear size (microm(2)) were higher in tendons from the loaded limb compared to the unloaded control limb. The purpose of the present study was to compare those results to results obtained with a repetition rate of 10 while maintaining the same peak force and force-time integral (n = 8). Due to a strain gradient between the inner and outer sides of the FDP tendon, microtears were quantified in four regions, two regions each along the inner and outer sides of the tendon. The tear area as a percent of total tendon area and the mean tear size were significantly greater in the loaded limb compared to the unloaded limb (p < 0.03). However, the effects were less than those observed at 60 repetitions/min. The higher repetition loading pattern resulted in an increase in tear measures in all four regions, while the lower rate produced changes only in the outer regions of the tendon. This finding may establish where the initial sites of damage occur in tendons that insert into bone in a similar arrangement as the FDP. The results suggest that repetition rate or number of loading cycles is associated with increased tendon microtears or fragility in a dose-response pattern.
我们之前报道过，在体内加载的兔趾长屈肌（FDP）肌腱中形成了微撕裂，加载频率为每分钟60次重复，峰值力为最大强直收缩力的15%，持续累积80小时。与未加载的对照肢体相比，加载肢体的肌腱中，撕裂面积占肌腱面积的百分比、撕裂密度（撕裂数/mm²）和平均撕裂大小（μm²）更高。本研究的目的是将这些结果与在重复频率为10次时获得的结果进行比较，同时保持相同的峰值力和力-时间积分（n = 8）。由于FDP肌腱内外侧之间存在应变梯度，在四个区域对微撕裂进行了量化，肌腱内外侧各两个区域。与未加载肢体相比，加载肢体中撕裂面积占总肌腱面积的百分比和平均撕裂大小显著更大（p < 0.03）。然而，这些影响小于在每分钟60次重复时观察到的影响。较高的重复加载模式导致所有四个区域的撕裂指标增加，而较低的频率仅使肌腱外侧区域发生变化。这一发现可能确定了在与FDP以类似排列方式插入骨骼的肌腱中，初始损伤部位的位置。结果表明，重复频率或加载周期数与肌腱微撕裂增加或脆性增加呈剂量反应模式相关。
