Design and Preliminary Evaluation of a Gait Control Strategy for Hip-Knee-Ankle-Foot Prostheses With Motorized Hip Joint.

Hip disarticulation (HD) amputees face mobility challenges due to the loss of hip, knee, and ankle joints. Current hip-knee-ankle-foot (HKAF) prostheses are entirely passive and require excessive compensatory movements to operate, leading to fatigue and long-term complications. Seeking to address these limitations, this study developed a HD user-centric, walking speed adaptable control strategy paired with a hip-motorized HKAF to emulate gait characteristics of transfemoral amputees. A prototype "Power Hip" was instrumented with internal sensors (IMUs, load cells, joint encoders) to create a prosthetic unit that could be worn without the need for external sensors. A hierarchical gait control strategy was developed to utilize these sensors to calculate the desired hip states and actuate the joint. To evaluate capabilities of the control strategy, an HD amputee participant was recruited to undergo training with Power Hip. Once training was complete, motion captured kinematics and onboard sensor data were analyzed across slow, self-paced, and fast walking speed trials. The Power Hip enabled walking speeds of 0.69-1.01 m/s, with stride parameters aligning with transfemoral amputee outcome measures. Hip extension velocities (60.2-104.9°/s) matched transfemoral kinematics, though swing-phase knee flexion magnitude and velocity were reduced compared to transfemoral benchmarks. The prototype demonstrated a 52° hip range of motion, surpassing conventional passive hip joints, and adapted to speed changes automatically. This research paves the way for advanced prosthetic solutions to improve quality of life for people with hip-level amputations.