Effects of Training with Hybrid Assistive Device on Motor Unit Behavior After Total Knee Arthroplasty: A Randomized Controlled Trial.

Authors

Takaya Watabe, Yuichi Nishikawa, Hisashi Naito, Ryota Muramatsu, Yuta Taniguchi

Published in

Annals of biomedical engineering. Jul 16, 2026. Epub Jul 16, 2026.

Abstract

Postoperative rehabilitation utilizing the single-joint Hybrid Assistive Limb (HAL-SJ) following total knee arthroplasty (TKA) has been reported to facilitate early functional recovery. This study aimed to elucidate the firing properties of individual motor units (MU) during knee exercise post-TKA with HAL-SJ assistance.
This single-blinded randomized controlled trial included 24 participants who underwent primary TKA for knee osteoarthritis. Participants were randomly assigned to the HAL-SJ (n = 12) or control (n = 12) groups. All participants followed the same postoperative rehabilitation protocol; however, those in the HAL-SJ group commenced training with the HAL-SJ 7-day post-surgery. The primary outcomes included the discharge rate (DR) obtained from high-density surface electromyography recordings from the vastus medialis (VM) and vastus lateralis (VL) muscles, which were measured preoperatively and 3 weeks postoperatively. The secondary outcomes included knee isometric extension torque and knee pain intensity, assessed using a numerical rating scale (NRS).
The DR of the VL muscle at 60% maximal voluntary contraction in the HAL-SJ group was significantly higher postoperatively compared to preoperatively (p = 0.001). In addition, the overall DR of the VL muscle in the HAL-SJ group was significantly higher than that in the control group for higher-threshold MU (HTMU) (p < 0.001). No significant differences were observed in knee extension torque or resting pain NRS scores between the control and HAL-SJ groups.
Rehabilitation with the HAL-SJ following TKA induced neurophysiological alterations in the VL muscle, characterized by an increased discharge rate of higher-threshold motor units. Although no significant between-group differences were observed in knee extension torque, these findings suggest that HAL-SJ training may facilitate early neural adaptations following TKA.
This study was registered with the University Hospital Medical Information Network (UMIN000053675).

PMID:
42463570
Bibliographic data and abstract were imported from PubMed on 17 Jul 2026.

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