Gefen Amit
Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv, 69978, Israel.
Med Biol Eng Comput. 2007 Jun;45(6):563-73. doi: 10.1007/s11517-007-0187-9. Epub 2007 May 8.
Pressure-related deep tissue injury is the term recommended by the United States National Pressure Ulcer Advisory Panel to describe a potentially life-threatening form of pressure ulcers, characterized by the presence of necrotic tissue under intact skin, and associated with prolonged compression of muscle tissue under bony prominences. In this study, a theoretical model was used to determine the relative contributions of the backrest inclination angle during prolonged wheelchair sitting, the muscle tissue stiffness and curvature of the ischial tuberosities (ITs) to the risk for injury in the gluteus muscles that pad the IT bones during sitting. The model is based on Hertz's theory for analysis of contact pressures between a rigid half-sphere (bone) and an elastic half-space (muscle). Hertz's theory is coupled with an injury threshold and damage law for muscle-both obtained in previous studies in rats. The simulation outputs the time-dependent bone-muscle contact pressures and the injured area in the gluteus. We calculated the full-size (asymptotic) injured area in the gluteus and the time for injury onset for different sitting angles alpha (90-150 degrees), muscle tissue long-term shear moduli G (250-1,200 Pa) and bone diameters D (8-18 mm). We then evaluated the sensitivity of model results to variations in these parameters, in order to determine how injury predictions are affected. In reclined sitting (alpha=150 degrees) the full-size injured area was approximately 2.1-fold smaller and the time for injury onset was approximately 1.3-fold longer compared with erect sitting (alpha=90 degrees). For greater G the full-size injured area was smaller but the time for injury onset was shorter, e.g., increasing G from 250 to 1200 Pa decreased the full-size injured area approximately 2.5-fold, but shortened the time for injury onset 6.2-fold. For smaller D the time for injury onset dropped, e.g., decreased approximately 1.5-fold when D decreased from 18 to 8 mm. Interestingly, the full-size injured area maximized at D of about 12 mm but decreased for smaller or larger D. The susceptibility to sitting-acquired deep tissue injury strongly depends on the geometrical and biomechanical characteristics of the bone-muscle interface, and, particularly, on the radius of curvature of the IT which mostly influenced the size of the wound, and on the muscle stiffness which dominantly affected the time for injury onset.
压力相关深部组织损伤是美国国家压疮咨询小组推荐的术语，用于描述一种可能危及生命的压疮形式，其特征是完整皮肤下存在坏死组织，并与骨隆突下肌肉组织的长时间受压有关。在本研究中，使用了一个理论模型来确定长时间坐轮椅时靠背倾斜角度、坐骨结节（ITs）的肌肉组织刚度和曲率对坐立时垫在IT骨上的臀肌损伤风险的相对贡献。该模型基于赫兹理论，用于分析刚性半球（骨头）和弹性半空间（肌肉）之间的接触压力。赫兹理论与肌肉的损伤阈值和损伤定律相结合——这两者均来自先前对大鼠的研究。该模拟输出随时间变化的骨 - 肌肉接触压力以及臀肌中的损伤面积。我们计算了不同坐姿角度α（90 - 150度）、肌肉组织长期剪切模量G（250 - 1200帕斯卡）和骨直径D（8 - 18毫米）时臀肌的全尺寸（渐近）损伤面积和损伤起始时间。然后，我们评估了模型结果对这些参数变化的敏感性，以确定损伤预测是如何受到影响的。与直立坐姿（α = 90度）相比，斜躺坐姿（α = 150度）时全尺寸损伤面积大约小2.1倍，损伤起始时间大约长1.3倍。对于更大的G，全尺寸损伤面积更小，但损伤起始时间更短，例如，将G从250帕斯卡增加到1200帕斯卡会使全尺寸损伤面积大约减小2.5倍，但损伤起始时间缩短6.2倍。对于更小的D，损伤起始时间下降，例如，当D从18毫米减小到8毫米时，损伤起始时间大约下降1.5倍。有趣的是，全尺寸损伤面积在D约为12毫米时达到最大值，但对于更小或更大的D则减小。坐立导致的深部组织损伤易感性强烈取决于骨 - 肌肉界面的几何和生物力学特征，特别是取决于主要影响伤口大小的IT曲率半径，以及主要影响损伤起始时间的肌肉刚度。
