Quantifying Lower Limb Sagittal Plane Alignment Based on 3D Scans: Method Validation and Implementation to Compare Conventional and Digital AFO Shape Capture Processes

Abstract

Lower limb alignment is a key aspect of ankle foot orthosis design which needs to be addressed in the development of digital technology workflows. The goal of this work was to develop a practical and accurate method to measure the sagittal plane ankle angle from 3D scans and investigate alignment differences achieved in conventional and digital shape capture processes. The sagittal plane ankle angle was measured by three orthotists using a digital goniometry tool and through an alignment algorithm. The digital goniometry tool was found to be a reliable method for measuring the sagittal plane ankle angle, and the algorithm produced measurements equivalent to the orthotists’ measures. Alignment differences were found between the digital and conventional shape capture processes ranging from 8° of dorsiflexion to 11° of plantarflexion. This work has highlighted the need for further investigation into a digital design process to enable the correction of the lower limb alignment.