Single-joint Hybrid Assistive Limb in Knee Rehabilitation after ACL Reconstruction: An Open-label Feasibility and Safety Trial

Abstract

Objectives: To achieve better outcomes, neuromuscular and biomechanical factors should be considered in rehabilitation after anterior cruciate ligament reconstruction. In this study, we investigated the feasibility and safety of a wearable exoskeleton robot suit [known as the single-joint hybrid assistive limb (HAL-SJ)] and whether knee training using this device could improve functional outcomes after anterior cruciate ligament reconstruction.

Methods: HAL-SJ-assisted knee extension and flexion exercises were commenced in 11 patients 18 weeks after reconstruction; exercises were performed once a week for three weeks at a frequency of five sets of ten repetitions. Patients were monitored for HAL-SJ-related adverse events. Physical evaluations were conducted before and after HAL-SJ training. Surface electromyography of the quadriceps and hamstring muscles was performed in 4 of the 11 patients during each session and the muscle co-contraction index was calculated.

Results: The peak muscle torque was higher at all velocities after HAL-SJ training. The active range of motion significantly increased in both extension and flexion, and the range of motion in passive flexion significantly increased. The Tegner Activity Scale and Lysholm Knee Questionnaire scores also significantly increased after knee HAL training. The muscle co-contraction index during extension tended to be lower after HAL-SJ training. No adverse events were observed.

Conclusions: The findings of this study indicate the feasibility and safety of HAL-SJ training as a neuromuscular rehabilitation tool after anterior cruciate ligament reconstruction. The knee HAL-SJ training may have contributed to these results from a neurophysiological perspective by lowering the co-contraction of knee muscles, which would correct impairment of the antagonistic or synergistic muscles.

Keywords: co-contraction index; limb symmetry index; neuromuscular rehabilitation tool.

Fig. 1.

Components of the single-joint hybrid assistive limb (HAL-SJ) and images of knee extension and flexion training with assistance of the HAL-SJ.

Fig. 2.

Limb symmetry index of (A) peak extension torque and (B) peak flexion torque for three angular velocities. Pre-HAL, before HAL-SJ training; Post-HAL, after HAL-SJ training.