Alternative methods for measuring ankle-foot orthosis alignment in clinical care

Abstract

Changes in gait due to an ankle foot orthosis (AFO) have been shown to be impacted by the sagittal plane alignment of the AFO, but there is variability in practice and lack of consensus as to how this alignment should be measured. The neutral angle is a measure of AFO alignment that has the potential to be used by various specialties that prescribe, provide, and analyze AFOs. Currently, a lack of validated measurement methods prevents the neutral angle from being used in various clinical settings. Two experimental neutral angle measurement methods are proposed to address this shortcoming: a portable low-cost method for use during AFO fabrication and fitting, and a laboratory-based method for use during dynamic three-dimensional gait analysis (3DGA). What is the concurrent validity of the two experimental neutral angle measurement methods against the gold standard? The gold standard neutral angle measurement (NAGOLD) was prospectively collected during a static 3DGA trial for 19 pediatric AFOs from 10 individuals. While NAGOLD was being collected, the neutral angle was simultaneously measured using digital differential inclinometers (NAINCL). Within the same 3DGA session, the neutral angle was also measured during the swing phase of gait (NASWING). The NAINCL and NASWING measurements were compared to NAGOLD using repeated measures ANOVA, ICC, and bootstrapped errors-in-variables regressions. Repeated measures ANOVA indicated no differences between measurement methods (p = 0.43) and ICC analysis indicated good absolute agreement (ICC(A-1) = 0.85). Mean absolute deviations between the NAINCL and NASWING with NAGOLD measurements were 2.4 ° and 1.9 °, with standard deviations of 2.9 ° and 2.7 °, respectively. Maximum observed differences were less than 7 °. The NAINCL and NASWING methods explained 74 % and 81 % of the variance in NAGOLD, respectively. The concurrent validity of two new neutral angle measurement methods provides alternative means to assess AFO alignment in the clinic.