Robinovitch S N, Chiu J
Division of Orthopaedic Surgery, San Francisco General Hospital and the University of California, San Francisco, 94110, USA.
J Orthop Res. 1998 May;16(3):309-13. doi: 10.1002/jor.1100160306.
Falls on the outstretched hand are among the most common causes of traumatic bone fracture. However, little is known regarding the biomechanical factors that affect the risk for injury during these events. In the present study, we explored how upper-extremity impact forces during forward falls are affected by modification of surface stiffness, an intervention applicable to high-risk environments such as nursing homes, playgrounds, and gymnasiums. Results from both experimental and linear biomechanical models suggest that during a fall onto an infinitely stiff surface, hand contact force is governed by a high-frequency transient (having an associated peak force Fmax1), followed by a low-frequency oscillation (having an associated lower magnitude peak force Fmax2). Practical decreases in surface stiffness attenuate Fmax1 but not Fmax2 or the magnitude of force transmitted to the shoulder. Model simulations reveal that this arises from the compliant surface's ability to decrease the velocity across the wrist damping elements at the moment of impact (which governs Fmax1) but inability to substantially reduce the peak deflection of the shoulder spring (which governs Fmax2). Comparison between model predictions and previous data on fracture force suggests that feasible compliant surface designs may prevent wrist injuries during falls from standing height or lower, because Fmax1 will be attenuated and Fmax2 will remain below injurious levels. However, such surfaces cannot prevent Fmax2 from exceeding injurious levels during falls from greater heights and therefore likely provide little protection against upper-extremity injuries in these cases.
伸出手时摔倒，是创伤性骨折最常见的原因之一。然而，对于这些事件中影响受伤风险的生物力学因素，我们却知之甚少。在本研究中，我们探究了向前摔倒时上肢冲击力如何受到表面刚度变化的影响，这种干预措施适用于养老院、操场和体育馆等高风险环境。实验和线性生物力学模型的结果均表明，在摔倒至无限坚硬表面的过程中，手部接触力由高频瞬态（伴有峰值力Fmax1）控制，随后是低频振荡（伴有较低幅度的峰值力Fmax2）。表面刚度的实际降低会减弱Fmax1，但不会减弱Fmax2或传递至肩部的力的大小。模型模拟显示，这是由于柔顺表面能够在撞击瞬间降低穿过腕部阻尼元件的速度（这决定了Fmax1），但无法大幅降低肩部弹簧的峰值挠度（这决定了Fmax2）。模型预测与先前骨折力数据的比较表明，可行的柔顺表面设计可能会预防站立高度及以下摔倒时的手腕损伤，因为Fmax1会减弱，且Fmax2将保持在损伤水平以下。然而，在从更高高度摔倒时，此类表面无法防止Fmax2超过损伤水平，因此在这些情况下可能无法为上肢损伤提供多少保护。
