Improvement of Walking Ability Using Hybrid Assistive Limb Training in a Patient with Severe Thoracic Myelopathy caused by Ossification of the Posterior Longitudinal Ligament-A Case Report

The purpose of this study was to report the improvement of walking ability using Hybrid Assistive Limb (HAL) training in a case of severe thoracic myelopathy caused by ossification of the posterior longitudinal ligament (OPLL). The patient received HAL training 2-3 times per week (10 sessions) beginning on the thirteenth postoperative day. The patient’s walking ability and lower muscles strength were significantly improved. It suggests that HAL training in the early postoperative phase has the potential to be an effective rehabilitation tool to improve functional ambulation in surgically-treated thoracic OPLL patients with inability of walk.


Introduction
It is estimated that 7,400 people (range 6,000 -8,900) in Japan have ossification of the posterior longitudinal ligament (OPLL), prevalence of 6.33 per 100,000 people [1]. Because OPLL causes spinal canal stenosis leading to mechanical compression of the spinal cord and nerve roots, clinical symptoms such as motor paralysis of the upper and lower-extremity, pain, sensory disturbance, and urinary disturbance are prevalent in cervical OPLL. Surgical treatment is chosen when there are deficits in finger dexterity, gait disturbance, urinary disturbance, or in cases in which conservative treatment is refractory.
The exoskeleton robot hybrid assistive limb (HAL) (Figure 1) can support the wearer's motion by adjusting the level and timing of the assistive torque provided to each joint according to the surface muscle action potential on the anterior and posterior surface of the wearer's thigh, as well as by using pressure sensors in the shoes [2]. The HAL can appear as an actual motion, and it can enhance the wearer's motion through their muscle action potential. The HAL training, using muscle activity, has the potential to intensify the feedback by inducing an appropriate motion more strongly than other standard robot training *Corresponding author: Masashi Yamazaki M.D, PhD, Department of Orthopaedic Surgery, Faculty of Medicine, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki, 305-8575, Japan. Tel: +81-29-853-3219; Fax: +81-29-853-3162; E-mail: masashiy@md.tsukuba.ac.jp [3][4][5][6]. Thus, after HAL training, patients with limited mobility can improve their walking abilities. The feasibility of rehabilitation using HAL training has been shown for multiple disorders [7], including training in eight patients with chronic spinal cord injuries [8]. However, for rehabilitation in case of severe thoracic myelopathy caused by OPLL, it is difficult to secure enough training quantity because of the burden on medical therapists. Even if a patient's condition were too severe for medical therapists to provide adequate rehabilitation training, HAL might still make adequate training possible. We report here the improvement of walking ability using the HAL training in a case of severe thoracic myelopathy caused by OPLL.

Case Report Patient
A 43-year-old man had numbness on the anterior the right femoral region four months prior that prevented him from walking. His paraplegia had progressed rapidly, and he was diagnosed with thoracic OPLL. He scored 3-4 on MMT (Manual muscle testing) for both lower limbs, and had sensory disturbance below the region of the umbilicus. In addition, he had urinary disturbance and the sphincter dysfunction. The CT (computed tomography) myelography and MRI (Magnetic resonance imaging) showed the spinal cord compression extending from T8-T11, and from L1 to L3 ( Figure 2). Thoracic level 10/11 was the most affected region, with approximately 80% of the spinal canal occupied by OPLL. The patient was able to walk 200 300 m using crutches bilaterally under supervision by postoperative day 55. He was discharged from our hospital to his home on postoperative day 65 (9 weeks after surgery). Functional ambulation was assessed with the 10-m walk test (10 MWT) and the walking index for spinal cord injury (WISCI) II [9]. In the 10 MWT, the patient was instructed to walk without wearing HAL on a flat surface at a self-selected, comfortable pace. To calculate gait speed (m/s) as a primary outcome, the 10-m walking time was measured using a handheld stopwatch. In addition, the number of steps between the start and finish line was counted, and patient cadence was calculated from the walking time and number of steps. The extent of spinal cord injury was assessed with the ASIA (American Spinal Injury Association) impairment scale (AIS), ASIA score (lower limbs), and JOA (Japanese Orthopaedic Association) score. ADL (Activities of daily living) were assessed with the FIM (functional independence measure) motor score and Barthel index (BI). Improvements in gait speed, steps, and cadence were observed gradually in the 10 MWT (Figures 5-7). Improvements in WISCI II was observed from level 13 (walker gait) to level 16 (two crutches) before and after the HAL training. The patient improved from 3 to 4-5 on the MMT in both lower limbs. Although we observed no change in AIS as D, improvements in the ASIA score (lower limbs) was observed from 26 to 50. Improvement in the JOA score, FIM motor score, and BI were observed from 1.5 to 5.5, from 44 to 81, and from 60 to 85, respectively (Table 1). No serious adverse events were observed during the rehabilitation training.
Posterior decompression with instrument fusion using rods surgery was performed from T7 to L3 (Figure 3). The patient was able to sit on the bed by the third postoperative day. Conventional physical training such as sitting exercise on the bed, standing exercise, and gait training with a walking device was started on the third postoperative day, and he was able to move in a wheelchair by the fourth at postoperative day. He started gait training with a walker one week after surgery. After that, he was able to ambulate with a pick up walker under supervision.

HAL Training
He received additional HAL training 2-3 times per week (10 sessions) starting two weeks after surgery (Figure 4). For safety reasons,

Discussion
Walking ability and muscle weakness of both legs were significantly improved after surgical treatment combined with HAL training in this case. Sakakima et al. reported that the walking ability of a thoracic OPLL patient with an inability to walk despite multiple surgeries was significantly improved using HAL training [10]. However, it takes a long time for paralysis to resolve before the patient can return home. HAL training has been applied to chronic spinal cord injuries, but there have been no previous reports on the effect of rehabilitation using HAL for severe thoracic spinal cord injuries (myelopathy) due to OPLL in the early phases of rehabilitation after surgical intervention.
Wu et al., reported that robotic resistance/assistance training using the original custom-designed cable-driven robotic gait training system improved gait speed, step length, and walking distance for the six minute walk test in 28 stroke patients with hemiplegia. Assistive training using the cable-driven robot during treadmill exercise might improve the motor learning mechanism. In addition, it was suggested that repetitive stepping assisted by the cable-driven robot might enhance the synaptic efficacy of sensorimotor pathways [11]. We have the impression that larger step length was observed during HAL training than conventional gait training in this case. Therefore, we think that HAL training affected the recovery of the motor function due to the motor learning. We also conjectured that the mechanism of this recovery of functional ambulation, sensory function, and coordination was due to changes in plasticity in the spinal cord and supraspinal centres by the HALinduced motion, which has favourable feedback effects. This is the first report that HAL training in the early postoperative phase has potential to improve a patient's mobility in severe thoracic spinal cord injury (myelopathy) due to OPLL with a prior inability to walk. The functional improvement in this case involved other treatment including both surgical treatment and conventional gait training. More patients will be needed to evaluate the isolated effects of HAL training.
This study was conducted with approval of the Ethics Committee of the Tsukuba University Faculty of Medicine.

Conflict of Interest
A commercial party having a direct financial interest in the results of the research supporting this article has conferred or will confer a financial benefit on 1 or more of the authors. Yoshiyuki Sankai is CEO of Cyberdyne Inc, Ibaraki, Japan. Hiroaki Kawamoto is a stockholder of the company. Cyberdyne is the manufacturer of the robot suit HAL. This study was proposed by the authors. Cyberdyne was not directly involved in the study design; collection, analysis, or interpretation of data; writing the report; or the decision to submit the paper for publication. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated (Shigeki Kubota, Tetsuya Abe, Kengo Fujii, Aiki Marushima, Tomoyuki Ueno, Ayumu Haginoya, Ayumu Endo, Hideki Kadone, Yukiyo Shimizu, Yasushi Hada, Akira Matsumura and Masashi Yamazaki).