Hybrid Assistive Limb Single Joint Type (HAL-SJ) Training for Knee Osteoarthritis: A Case Series

Knee osteoarthritis (OA) is a common degenerative joint condition in older adults, and pain often limits engagement in conventional exercise therapy. We report three cases of patients with Kellgren-Lawrence (KL) grade 3 KO who underwent rehabilitation using the Hybrid Assistive Limb Single Joint Type (HAL-SJ), a wearable robotic device that supports voluntary knee movement based on bioelectrical signals from muscle activity. All patients completed 10 training sessions over five weeks with no serious adverse events. The intervention was well tolerated, and no clinically significant deterioration in symptoms was observed during the training period. Knee pain decreased in two cases and remained unchanged in one case. These cases suggest that HAL-assisted knee training is feasible and safe for patients with moderate knee OA and may offer potential clinical benefits.