The Biomechanical Impact of Joint Axis Misalignment in Hinged Ankle-Foot Orthoses
Böhm H, Spelly G, Miehling J, Müller M, Hildebrandt-Ahlborn M, Bellmann M (2025)
Publication Type: Journal article
Publication year: 2025
Journal
Book Volume: 121
Pages Range: 37
DOI: 10.1016/j.gaitpost.2025.07.044
Abstract
Introduction
Ankle-foot orthoses (AFOs) are essential for supporting gait and joint stability, especially in individuals with neuromuscular impairments. In hinged AFOs, the alignment of the orthotic joint axis is usually based on manufacturer guidelines rather than patient-specific biomechanics. Misalignment may alter joint loading, restrict ankle range of motion, and cause pistoning—shaft-to-leg movement that can reduce comfort and effectiveness [1]. This study examines how deviations in joint axis positioning affect the mechanical performance and user interaction with AFOs.
Research Question
This study investigates the biomechanical effects of anterior-posterior and proximal-distal shifts in the joint axis of bilateral hinged AFOs. It explores whether anterior-posterior shifts more strongly influence ankle plantarflexion moments than proximal-distal shifts, and whether all deviations induce pistoning and restrict ankle range of motion relative to a shod condition.
Methods
Six healthy adult males (35 ± 12 years) participated in gait trials under six conditions: five bilateral individually fitted AFO configurations with joint axis positions varied (anterior, posterior, proximal, distal, and neutral) and one shod condition. Kinematic and kinetic data were captured using a 3D motion analysis system. Outcomes included ankle joint moments, ankle range of motion, and pistoning between the orthotic shaft and leg. Additionally, musculoskeletal simulations were performed in OpenSim using a modified, individually scaled Gait2392 model. In this setup, the foot was rigidly attached to the orthosis while the shaft was allowed to move, enabling estimation of internal ankle joint moments across different alignment conditions
Results
Anterior-posterior axis shifts significantly influenced ankle joint mechanics. Anterior alignment generated the smallest dorsiflexion moments and reduced pistoning during dorsiflexion. Proximal-distal shifts had minimal effect on ankle joint moments but resulted in increased pistoning. All orthotic conditions demonstrated reduced ankle range of motion compared to the shod condition. The neutral axis position, as recommended by the manufacturer, did not consistently minimize pistoning or preserve range of motion. Simulated internal joint moments showed no significant differences across the various axis alignments.
Discussion
This study demonstrates that anterior-posterior alignment of AFO joint axes has a more pronounced effect on ankle joint function than proximal-distal positioning. Anterior axis alignment reduced pistoning and enhanced joint kinetics, suggesting clinical benefits in terms of comfort and gait efficiency. The neutral alignment, while commonly recommended, did not provide superior mechanical performance. Proximal-distal variations had limited biomechanical relevance but did increase shaft-to-leg movement. Musculoskeletal simulations, though useful, were limited by the fixed-foot modeling assumption, which may have underestimated push-off dynamics, and indicates a necessity of precise interaction modelling between foot and orthosis. Overall, personalized joint axis alignment that closely matches anatomical motion may improve AFO outcomes by preserving joint mechanics, reducing pistoning, and enhancing user comfort.
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Germany (DE)How to cite
APA:
Böhm, H., Spelly, G., Miehling, J., Müller, M., Hildebrandt-Ahlborn, M., & Bellmann, M. (2025). The Biomechanical Impact of Joint Axis Misalignment in Hinged Ankle-Foot Orthoses. Gait & Posture, 121, 37. https://doi.org/10.1016/j.gaitpost.2025.07.044
MLA:
Böhm, Harald, et al. "The Biomechanical Impact of Joint Axis Misalignment in Hinged Ankle-Foot Orthoses." Gait & Posture 121 (2025): 37.
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