Quantifying alignment bias during the fabrication and fitting of ankle-foot orthoses: A single center study

Background: The sagittal plane alignment of ankle-foot orthoses (AFO) and AFO footwear combinations (AFO-FC) has been shown to influence gait outcomes. As such, clinicians often target a particular alignment during the fabricating and fitting of an AFO to maximize outcomes. Research question: How does the alignment of an AFO change during the fabrication and fitting process with respect to the intended, benchmark sagittal plane alignment identified by the consulting orthotist? Study design: Prospective Methods: The assessment of AFO alignment was performed using a convenience sample of 125 custom molded AFOs from 68 individuals fabricated at our center (57 bilateral AFOs, 11 unilateral AFOs). The alignment of each AFO was measured at 5 distinct steps during the fabrication and fitting process using a recently validated method to measure AFO neutral angle using differential inclinometers. Results: Prior to fabrication, the intended, benchmark alignment set by the consulting orthotist was 90 degrees for 92% of AFOs, was between 1 and 7 degrees of dorsiflexion for 7% of AFOs and was 5 degrees of plantarflexion for 1% of AFOs. Repeated measures ANOVA showed that AFO alignment changed between all fabrication and fitting steps. Overall, paired t-tests confirmed that AFO alignment was consistently 2–5 degrees more dorsiflexed than the benchmark alignment. Prior to fitting shoes, 55% of fabricated AFOs measured more than 2 degrees from the benchmark alignment. After fitting shoes, nearly 87% of AFO-FCs were more than 2 degrees from the benchmark alignment. Significance: The finding of systematic dorsiflexion bias and changes in AFO alignment throughout the fabrication and fitting process indicates the need to improve AFO fabrication precision. The neutral angle measurement methodology – using differential inclinometers – provides a means to improve this precision by enabling orthotists to precisely quantify and make appropriate adjustments to AFO alignment throughout the entire fabrication and fitting process.