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Additional file 5: Data of the kinematic motion analysis of the knee joint for HAL session 4. (A) Temporal profile of the angular position of the knee joint over the gait cycle (A) and range of motion of the knee over the gait cycle (B), measured without, immediately before, and after the HAL training. Error bars indicate standard error of the mean. Flex, flexion; Ext, extension; Pre, Pre-HAL training; Post, Post-HAL training; ROM, range of motion.

Additional file 6: The 10-m walk test data immediately before and after HAL gait training, sessions 1���10. Gait speed (A), step length (B), and cadence (C).

Although postoperative recurrent lumbar disc herniation (rec-LDH) is uncommon, it is a challenging situation that requires revision surgery when conservative treatment fails. Recently, an agent inducing chemical dissolution of the nucleus pulposus using condoliase has been approved as a novel intradiscal treatment for LDH. To date, no evidence has been reported regarding its effectiveness in the treatment of postoperative rec-LDH. A 25-year-old man with a history of LDH in L4/5, who underwent transforaminal full endoscopic lumbar discectomy when he was 17 years old, complained of severe pain radiating to his left leg since 1 month. The straight leg-raising test was limited to 25° on the left side. Lumbar T2-weighted magnetic resonance imaging (MRI) showed intracanal, left-sided transligamentous disc herniation at L4/5 with high-signal intensity. Because the conservative treatment with oral analgesics and selective left L5 nerve root block failed, the patient requested intradiscal condoliase injection instead of revision surgery. There were no adverse events reported after the condoliase treatment, and the pain radiating to the left leg improved within 2 weeks. A lumbar MRI performed 2 months after treatment revealed that the disc herniation had significantly decreased in size. The straight leg-raising test examined 3 months after treatment was negative. In this case, the disc herniation was of the transligamentous type and showed a high-signal intensity on T2-weighted MRI which could be suitably treated by condoliase injection therapy. This case report is the first to suggest that intradiscal condoliase injection could be a useful and novel conservative treatment option to treat postoperative rec-LDH.

Additional file 9: Kinematic motion analysis using the VICON motion capture system and surface electromyography (HAL session 4). (A) Surface electromyography of the gastrocnemius muscles of the right and left legs during the stance and swing phases. (B) Gastrocnemius stance ratio of the right and left legs before, during, and after the HAL gait training. The gastrocnemius stance ratio indicates the muscle activation ratio of the gastrocnemius (swing phase to the total step cycle). Pre, Pre-HAL training; Post, Post-HAL training.

Additional file 2: Magnetic resonance (MR) images of the cervical and thoracic spine 14 months after surgery. T1-weighted (A) and T2-weighted (B) midsagittal MR images show sufficient decompression of the spinal cord at the thoracic spine. Magnification of the T2-weighted image at the cervical spine area (C) shows slight posterior compression of the spinal cord at the C3���C4 level (red arrow).

Additional file 1: Reconstruction images from computed tomography (CT) myelography of the cervical and thoracic spine before surgery. Midsagittal reconstruction CT myelogram of the cervical spine (A) and axial CT image at the C5 level (B) reveal segmental ossification of the longitudinal ligament (OPLL) at the C4���C6 vertebrae. The asterisks in (A) and (B) indicate the C5 OPLL. The spinal cord was compressed from the anterior and posterior directions at the C3���C4 and C4���C5 levels (red arrows). Midsagittal reconstruction CT myelogram of the thoracic spine (C) and axial CT image at the T4���T5 level (D) reveal multilevel ossification of the ligamentum flavum (OLF) at the T3���T8 vertebrae. The asterisks in (C) and (D) indicate the T4���T5 OLF. The spinal cord was compressed posteriorly at the T4���T5 level (blue arrow).

Additional file 7: Data of the kinematic motion analysis of step length for HAL session 4. Step length of the right and left legs immediately before and after HAL training. Pre, Pre-HAL training; Post, Post-HAL training.

Additional file 8: Data of the kinematic motion analysis of toe clearance for HAL session 4. Toe lift of the right and left legs before, during, and after HAL gait training. The toe lift indicates toe clearance. Pre, Pre-HAL training; Post, Post-HAL training.

Additional file 4: Data of the kinematic motion analysis of the hip joint for HAL session 4. (A) Temporal profile of the angular position of the hip joint over the gait cycle (A) and range of motion of the hip over the gait cycle (B), measured without, immediately before, and after the HAL training. Error bars indicate standard error of the mean. Flex, flexion; Ext, extension; Pre, Pre-HAL training; Post, Post-HAL training; ROM, range of motion.

We report a case of cardiac arrest, which occurred during C1 laminectomy for irreducible atlantoaxial subluxation, with return of spontaneous circulation (ROSC) upon interruption of the laminectomy. A 60-year-old woman with rheumatoid arthritis presented with neck pain, bilateral finger numbness, and bladder-rectal disturbance. Simple radiograph images showed that the atlantodental interval (ADI) was enlarged to 8 mm, and magnetic resonance imaging revealed severe spinal stenosis at C1. She was diagnosed with cervical spondylotic myelopathy due to atlantoaxial subluxation. Cardiac arrest occurred twice during the C1 laminectomy and occipito-cervical fusion (Occ-C3), and ROSC occurred without any treatment. There was no postoperative worsening of neurological symptoms, and the improvement of sensory and motor palsy was favorable. The pathogenic mechanism was presumed to be trigeminocardiac reflex. Cardiac arrest during upper cervical spine surgery is an important intraoperative complication of which operators should be made aware.

Several reports have described the coexistence of spina bifida occulta (SBO) and spondylolysis, but the majority of defects occur at L5. No report has described the coexistence of SBO and spondylolysis at the thoracolumbar junction. We report a case of SBO with spondylolysis at L1, presenting cauda equine syndrome. A 37-year-old man presented with a gait disorder as a result of bilateral motor weakness of the lower extremities. A plain radiograph showed local kyphosis at L1-2 as a result of severe degenerative change and wedging of the vertebral body at L1. Magnetic resonance imaging (MRI) revealed degenerative disc changes and severe canal stenosis at L1-2. Computed tomography (CT) revealed SBO and spondylolysis at L1. He was diagnosed with cauda equina syndrome related to SBO and spondylolysis at L1. Posterior interbody fusion and decompression at L1-2 were performed. After surgery, his muscle power recovered to normal strength. The possible mechanisms in this case are the strain on anterior elements as a result of disruption of the posterior elements due to SBO and spondylolysis. The coexistence of SBO and spondylolysis at the thoracolumbar junction might induce at-risk status of increased strain to the anterior elements that may cause cauda equina syndrome.

Although adjacent segmental disease after posterior thoracic fusion surgery is rare, thoracic myelopathy due to ossification of the yellow ligament in the lower thoracic spine could develop because of mechanical stress when the lower instrumented vertebra has been set to the middle thoracic spine during the initial surgery. We report an extremely rare case of distal adjacent segmental disease after posterior cervical-middle thoracic fusion surgery requiring reoperation after exhibiting thoracic myelopathy due to ossification of the yellow ligament in the lower thoracic spine. An obese 53-year-old man with diabetes had undergone C3-6 laminoplasty and C7-T8 posterior decompression plus fusion due to ossification of the posterior longitudinal ligament at C5-T5. Although the short-term clinical course after the initial surgery was good, symptoms of myelopathy reappeared because of the ossification of the yellow ligament that developed at T9-11 with local flexibility. Thus, reoperation with fusion extension surgery was needed 1 year and 6 months after the initial surgery. Altogether, we recommend careful monitoring of the postoperative clinical progression and, if necessary, reoperation at the earliest.