Active knee–ankle–foot orthosis with personalized knee trajectory compared with locked orthosis and multi-joint exoskeleton

Assistive walking devices after spinal cord injury (SCI) should balance functional gait assistance with practical usability. This study presents a user-priority-guided pathway that links a needs-assessment survey to minimal actuation in a knee-ankle-foot orthosis (active KAFO) and objective-driven personalization of knee motion. A retrofit prototype with a single powered knee joint was implemented to preserve the orthosis-like form factor while enabling personalized, impedance-controlled knee motion. Personalization was formulated in OpenSim as a kinematic optimization, where a low-dimensional knee-trajectory template was tuned using a sagittal foot-path objective, coordinate tracking, smoothness regularization, and feasibility constraints. The optimized trajectory was deployed during overground walking in one individual with SCI and compared within subject against a locked KAFO and a multi-joint exoskeleton. Relative to the locked condition, the personalized active-KAFO condition improved swing-phase outcomes, increasing step length by 38.6% and step height by 100.0%. It also reduced reliance on upper-limb support, with peak vertical walker force decreasing by 35.0%. Compared with the active KAFO, the exoskeleton showed similar step height (+ 2.2%) and swing speed (- 10.2%), but greater limb progression, with step length increasing by 19.7%. These feasibility-level results support personalized, knee-focused actuation as an intermediate option between locked orthoses and multi-joint exoskeletons.