Biomechanical evaluation of a novel fiberglass reinforced polyamide custom ankle-foot orthosis: gait analysis and energy assessment in a population of mild foot-drop patients

Ankle foot orthoses (AFOs) are medical devices used to stabilize the ankle following traumatic injuries, or lesion to the central or peripheral nervous systems leading to foot-drop. This represents the inability to lift the foot during the swing phase of walking, due to neuro-muscular impairments of the ankle dorsiflexor muscles. Mild foot-drop patients may need a comfortable AFO that provides support to the ankle and that can bend seamlessly with the physiological ankle motion in common daily motor tasks. While off-the-shelf AFOs are cost-effective solutions, they may not fully comply with the foot and leg shape and the patient-specific functional requirements. Over the last 20 years, advancements in additive manufacturing technologies have allowed to manufacture custom orthotic devices that better fit the affected anatomical segment. This thesis aimed at evaluating the functional and biomechanical outcome of a novel fiberglass-reinforced polyamide passive-dynamic custom AFO, manufactured via Selective Laser Sintering, in a population of foot-drop patients (n = 10; age = 64.9 ± 11.4 years, BMI = 26.2 ± 2.1 kg/m2). The energy absorbed and released by the custom AFO during the stance phase of walking has been estimated from its experimentally-measured stiffness and motion tracked via a 8-camera motion analysis system. The functional evaluation was assessed via gait analysis in the three conditions: shod (no-AFO), wearing an off-the-shelf AFO (a Codivilla spring) and wearing the custom AFO. Kinematics and kinetics of the hip, knee and ankle joints were estimated via skin-markers attached to relevant bony landmarks according to the IOR-gait kinematic protocol. Both AFOs resulted in decreased sagittal-plane range of motion of the ankle in the swing phase of gait, as well as in reduced plantarflexion angle. Spatiotemporal parameters analysis showed a significant increased stance time (63.7 ± 1.5 vs 63.7 ± 2.1 vs 61.0 ± 2.7 [% stride time]), normalized speed of walking (52.3 ± 12.9 vs 51.8 ± 14.1 vs 49.3 ± 13.9 [% height/s]) and normalized stride length (64.7 ± 11.0 vs 64.2 ± 11.6 vs 63.3 ± 11.3 [% height]) for the custom AFO with respect to the off-the-shelf one and to the shod condition. The energetic evaluation highlighted that the custom AFO releases part of the stored energy at foot-off thus contributing to the propulsive phase. Moreover, patients perceived the custom AFO more comfortable than the Codivilla spring (VAS score: 8.6 ± 1.2 vs 5.3 ± 1.3). This study provides evidence for the beneficial functional outcomes of AFO personalization, especially for mild foot-drop patients not satisfied with standard orthotics.