Center for Limb Loss and Mobility, VA Puget Sound, 1660 S Columbian Way, Seattle, WA, USA.
The Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc., Bethesda, MD, USA.
J Neuroeng Rehabil. 2023 Jan 22;20(1):11. doi: 10.1186/s12984-023-01126-7.
The mechanical properties of an ankle-foot orthosis (AFO) play an important role in the gait mechanics of the end user. However, testing methodologies for evaluating these mechanical properties are not standardized. The purpose of this study was to compare five different evaluation frameworks to assess AFO stiffness.
The same 13 carbon composite AFOs were tested with five different methods. Four previously reported custom test fixtures (the BRUCE, KST, SMApp, and EMPIRE) rotated an AFO into dorsiflexion about a defined axis in the sagittal plane. The fifth method involved quasi-static deflection of AFOs into dorsiflexion by hanging weights (HW) from the footplate. AFO rotational stiffness was calculated as the linear fit of the AFO resistive torque and angular deflection. Differences between methods were assessed using descriptive statistics and a repeated measures Friedman with post-hoc Bonferroni-Holm adjusted Wilcoxon signed-rank tests.
There were significant differences in measured AFO stiffnesses between test methods. Specifically, the BRUCE and HW methods measured lower stiffness than both the EMPIRE and the KST. Stiffnesses measured by the SMApp were not significantly different than any test method. Stiffnesses were lowest in the HW method, where motion was not constrained to a single plane. The median difference in absolute AFO stiffness across methods was 1.03 Nm/deg with a range of [0.40 to 2.35] Nm/deg. The median relative percent difference, measured as the range of measured stiffness from the five methods over the average measured stiffness was 62% [range 13% to 156%]. When the HW method was excluded, the four previously reported test fixtures produced a median difference in absolute AFO stiffness of 0.52 [range 0.38 to 2.17] Nm/deg with a relative percent difference between the methods of 27% [range 13% to 89%].
This study demonstrates the importance of developing mechanical testing standards, similar to those that exist for lower limb prosthetics. Lacking standardization, differences in methodology can result in large differences in measured stiffness, particularly for different constraints on motion. Non-uniform measurement practices may limit the clinical utility of AFO stiffness as a metric in AFO prescription and future research.
踝足矫形器（AFO）的机械性能在终端用户的步态力学中起着重要作用。然而，评估这些机械性能的测试方法尚未标准化。本研究的目的是比较五种不同的评估框架来评估 AFO 刚度。
使用五种不同的方法对相同的 13 个碳纤维复合材料 AFO 进行测试。四个先前报道的定制测试夹具（BRUCE、KST、SMApp 和 EMPIRE）绕矢状面中定义的轴将 AFO 旋转至背屈。第五种方法通过从脚板上吊重物（HW）使 AFO 进入背屈，从而产生准静态挠度。AFO 旋转刚度被计算为 AFO 阻力扭矩和角度偏转角的线性拟合。使用描述性统计和重复测量 Friedman 检验，以及事后 Bonferroni-Holm 调整 Wilcoxon 符号秩检验来评估方法之间的差异。
测试方法之间的 AFO 刚度测量值存在显著差异。具体来说，BRUCE 和 HW 方法测量的刚度低于 EMPIRE 和 KST 方法。SMApp 方法测量的刚度与任何测试方法均无显著差异。HW 方法中的刚度最低，因为运动不受限于单个平面。方法之间绝对 AFO 刚度的中位数差异为 1.03 Nm/deg，范围为[0.40 至 2.35] Nm/deg。以五种方法中测量的刚度范围与平均测量刚度的中位数相对百分比差异，测量为 62%[范围 13%至 156%]。当排除 HW 方法时，之前报道的四个测试夹具产生的绝对 AFO 刚度中位数差异为 0.52 Nm/deg[范围 0.38 至 2.17]，方法之间的相对百分比差异为 27%[范围 13%至 89%]。
本研究表明，需要制定类似于下肢假肢的机械测试标准。缺乏标准化，方法上的差异可能导致测量刚度有很大差异，特别是对于运动的不同限制。非统一的测量实践可能会限制 AFO 刚度作为 AFO 处方和未来研究中的指标的临床应用。
