The voluntary driven exoskeleton Hybrid Assistive Limb (HAL) for postoperative training of thoracic ossification of the posterior longitudinal ligament: a case report

Context: The hybrid assistive limb (HAL) is a wearable robot suit that assists in voluntary control of knee and hip joint motion by detecting bioelectric signals on the surface of the skin with high sensitivity. HAL has been reported to be effective for functional recovery in motor impairments. However, few reports have revealed the utility of HAL for patients who have undergone surgery for thoracic ossification of the posterior longitudinal ligament (thoracic OPLL). Herein, we present a postoperative thoracic OPLL patient who showed remarkable functional recovery after training with HAL. Findings: A 63-year-old woman, who could not walk due to muscle weakness before surgery, underwent posterior decompression and fusion. Paralysis was re-aggravated after the initial postoperative rising. We diagnosed that paralysis was due to residual compression from the anterior lesion and microinstability after posterior fixation, and prescribed bed rest for a further 3 weeks. The incomplete paralysis gradually recovered, and walking training with HAL was started on postoperative day 44 in addition to standard physical therapy. The patient underwent 10 sessions of HAL training until discharge on postoperative day 73. Results of a 10-m walk test were assessed after every session, and the patient's speed and cadence markedly improved. At discharge, the patient could walk with 2 crutches and no assistance. Furthermore, no adverse events associated with HAL training occurred. Conclusion: HAL training for postoperative thoracic OPLL patients may enhance improvement in walking ability, even if severe impairment of ambulation and muscle weakness exist preoperatively.