Ewers B J, Jayaraman V M, Banglmaier R F, Haut R C
Orthopaedic Biomechanics Laboratories, Michigan State University.
Stapp Car Crash J. 2000 Nov;44:299-313. doi: 10.4271/2000-01-SC20.
accidents are often overlooked, but can have a profound societal cost. Knee injuries, for example, account for approximately 10% of the total injuries. Fracture of the knee is not only an acute issue but may also have chronic, or long term, consequences. The criterion currently used for evaluation of knee injuries in new automobiles, however, is based on experimental impact data from the 70's using seated human cadavers. These studies involved various padded and rigid impact interfaces that slightly alter the duration of contact. Based on these data and a simple mathematical model of the femur, it appears fracture tolerance increases as contact duration shortens. In contrast, more recent studies have shown mitigation of gross fractures of the knee itself using padded interfaces. The use of padded interfaces, however, result in coincidental changes in contact duration and knee contact area. Therefore, it is difficult to extract the direct effect of loading rate on fracture tolerance of the knee. The object of the current study was to isolate the effect of loading rate alone on fracture tolerance of the human knee joint. Paired experiments were conducted on eight pairs of isolated cadaver knees impacted with a rigid interface to approximately 5 kN at a high (5 ms to peak) or low (50 ms to peak) rate of loading. Gross fracture and occult microfractures of the knee joint were documented. A second part of the study examined some chronic effects of loading rate on "subfracture" injuries in an animal. Thirty-four rabbits were subjected to a "subfracture" knee load at the same rates as used in the human studies. Alterations in the mechanical properties of retropatellar cartilage and thickening of subchondral bone were documented out to one year post "subfracture" trauma to the joint. The current study documented an opposite effect than that expected based on 70's experiments with seated cadavers. There was an increase in the number of gross fractures and occult microfractures in high versus low rate of loading experiments. A similar effect was also seen in the "subfracture" chronic animal experiments, which showed relatively more degradative change in the mechanical properties of cartilage following high versus low rate of loading experiments. There was also a significant increase in subchondral bone thickening underlying cartilage and increased fissuring of cartilage in high versus low rate of loading experiments. The current study suggests a relative decrease in tolerance of the knee at high versus low rates of loading in acute experiments with human cadavers and in the chronic setting with animals. Therefore, it would appear that rate of knee loading may be an important issue in establishing a future injury criterion for the knee itself.
事故常常被忽视，但可能会带来巨大的社会成本。例如，膝盖损伤约占总损伤的10%。膝盖骨折不仅是一个急性问题，还可能产生慢性或长期后果。然而，目前用于评估新型汽车中膝盖损伤的标准是基于20世纪70年代使用坐姿人体尸体的实验冲击数据。这些研究涉及各种有衬垫和刚性的冲击界面，它们会略微改变接触持续时间。基于这些数据和一个简单的股骨数学模型，似乎骨折耐受性会随着接触持续时间的缩短而增加。相比之下，最近的研究表明使用有衬垫界面可减轻膝盖本身的严重骨折。然而，使用有衬垫界面会导致接触持续时间和膝盖接触面积同时发生变化。因此，很难提取加载速率对膝盖骨折耐受性的直接影响。本研究的目的是单独分离加载速率对人体膝关节骨折耐受性的影响。对八对分离的尸体膝盖进行了配对实验，用刚性界面以高（5毫秒达到峰值）或低（50毫秒达到峰值）加载速率冲击至约5千牛。记录了膝关节的严重骨折和隐匿性微骨折情况。该研究的第二部分考察了加载速率对动物“亚骨折”损伤的一些慢性影响。34只兔子接受了与人体研究相同速率的“亚骨折”膝盖负荷。记录了关节“亚骨折”创伤后长达一年的髌后软骨力学性能变化和软骨下骨增厚情况。本研究记录的结果与基于20世纪70年代对坐姿尸体实验所预期的结果相反。在高加载速率与低加载速率实验中，严重骨折和隐匿性微骨折的数量有所增加。在“亚骨折”慢性动物实验中也观察到了类似的效果，该实验表明，与低加载速率实验相比，高加载速率实验后软骨力学性能出现相对更多的降解变化。在高加载速率与低加载速率实验中，软骨下骨增厚以及软骨裂隙增加也有显著增加。本研究表明，在人体尸体急性实验和动物慢性实验中，高加载速率与低加载速率相比，膝盖的耐受性相对降低。因此，在为膝盖本身建立未来的损伤标准时，膝盖加载速率可能是一个重要问题。
