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Purpose <p>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.</p> Methods <p>This single-blinded randomized controlled trial included 24 participants who underwent primary TKA for knee osteoarthritis. Participants were randomly assigned to the HAL-SJ (<i>n</i> = 12) or control (<i>n</i> = 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).</p> Results <p>The DR of the VL muscle at 60% maximal voluntary contraction in the HAL-SJ group was significantly higher postoperatively compared to preoperatively (<i>p</i> = 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) (<i>p</i> &lt; 0.001). No significant differences were observed in knee extension torque or resting pain NRS scores between the control and HAL-SJ groups.</p> Conclusion <p>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.</p> Trial Registration <p>This study was registered with the University Hospital Medical Information Network (UMIN000053675).</p>

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

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月16日

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

摘要

Purpose

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.

Methods

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).

Results

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.

Conclusion

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.

Trial Registration

This study was registered with the University Hospital Medical Information Network (UMIN000053675).