Design and evaluation of the SMApp: A stiffness measurement apparatus for ankle–foot orthoses

Totah, Deema; Menon, Meghna; Gates, Deanna H.; Barton, Kira

doi:10.1016/j.mechatronics.2021.102572

Cited by 10 publications

(10 citation statements)

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“…Methodological differences across test fixtures are summarized in Table 1 . Further detail on the design of each test fixture can be found in previous publications (BRUCE [ 6 ], KST [ 10 ], SMApp [ 11 ], and EMPIRE [ 12 ]). We also used a simple method to quasi-statically load an AFO by manually measuring deflections from known loads (see ‘ Hanging weights method ’, Fig.…”

Section: Methodsmentioning

confidence: 99%

“…In accordance with prior literature describing the test methodologies, raw data collected on the KST were not filtered while data collected on the BRUCE and EMPIRE were low-pass filtered at 10 and 1 Hz, respectively [ 6 , 12 ]. In the SMApp, any signal artifacts were identified as sample-to-sample variations greater than 10 deg or 10 N (corresponding to about 350 deg/s or N/s slope) and removed from the raw time signals [ 11 ]. For the SMApp and EMPIRE, we applied calibration curves to adjust the measured load cell data to account for the gravitational loads and mechanical losses of the test fixture.…”

Section: Methodsmentioning

confidence: 99%

“…For consistency across all testing devices, AFO stiffnesses were computed as the linear fit of the torque angle curve for each cycle while moving into dorsiflexion [ 12 ]. To avoid periods of acceleration and deceleration when transitioning between plantarflexion and dorsiflexion, the stiffness was calculated over a smaller range of deflection than the total range of motion (Additional file 2 : Table S2) [ 11 , 12 ]. For those AFOs tested at the full range of motion, AFO stiffness was computed between 0 and 18 degrees of dorsiflexion.…”

Section: Methodsmentioning

confidence: 99%

“…Methodological differences include inconsistencies with mounting, alignment/bending axis, range of motion, and testing speed [ 1 , 4 , 5 ]. Only one study has directly compared AFO properties with two devices across three AFOs [ 11 ]. While similar stiffnesses were found in that study, it is unclear whether those results are generalizable across a range of AFO designs and materials or to other testing devices.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, the goal of this study was to compare the stiffnesses of carbon composite AFOs evaluated using methodologies that have been reported in the literature. The first four methods were previously reported test fixtures evaluated for repeatability: The Bi-articular Reciprocating Universal Compliance Estimator (BRUCE) [ 6 ], Kentucky Stiffness Tester (KST) [ 10 ], the AFO Stiffness Measurement Apparatus (SMApp) [ 11 ] and the device for Evaluating Mechanical Properties In Rotating Exoskeletons (EMPIRE) [ 12 ]. The fifth method manually measured the deflection of an AFO elicited from hanging weights off of the toe, similar to the approach used in previous studies [ 17 – 19 ].…”

Section: Introductionmentioning

confidence: 99%

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Comparison of five different methodologies for evaluating ankle–foot orthosis stiffness

Shuman

Totah

Gates

et al. 2023

J NeuroEngineering Rehabil

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Background 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. Method 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. Results 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%]. Conclusions 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.

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Section: Methodsmentioning

confidence: 99%