Abstract
Ossification of the posterior longitudinal ligament (OPLL) is a hyperostonic condition in which the posterior longitudinal ligament becomes thick and loses its flexibility, resulting in ectopic ossification and severe neurologic deficit (Matsunaga and Sakou, 2012). It commonly presents with myelopathy and radiculopathy and with myelopathy progression motor disorders and balance disorders can appear. Even after appropriate surgical decompression, some motor impairments often remain. The Hybrid Assistive Limb (HAL) is a wearable powered suit designed to assist and support the user's voluntary control of hip and knee joint motion by detecting bioelectric signals from the skin surface and force/pressure sensors in the shoes during movement. In the current study, the HAL intervention was applied to 15 patients diagnosed with OPLL who presented with myelopathy after decompression surgery (6 acute and 9 chronic stage). Following the HAL intervention, there were significant improvements in gait speed, cadence, stride length, in both acute and chronic groups. Joint angle analysis of the lower limbs showed that range of motion (ROM) of hip and knee joints in acute group, and also ROM of hip joint and toe-lift during swing in chronic group increased significantly. ROM of knee joint became closer to healthy gait in both groups. Electromyography analysis showed that hamstrings activity in the late swing phase increased significantly for acute patients. Immidiate effect from HAL session was also observed. EMG of vastus medialis were decreased except chronic 7th session and EMG of gastrocnemius were decreased except acute 7th session, which suggests the patients were learning to walk with lesser knee-hypertension during the sessions. After all, double knee action appeared in both acute and chronic groups after the HAL intervention, rather than knee hyper-extension which is a common gait impairment in OPLL. We consider that these improvements lead to a smoother and healthier gait motion.
Highlights
Myelopathy refers to a pathology that causes neurological deficits in the spinal cord (Oyinkan Marquis and Capone, 2016), that usually results from compression of the spinal cord by osteophytes or extruded intervertebral disks between the cervical spine (Seidenwurm, 2008)
Kinematic data from eight healthy volunteers (3 male, 5 female) who did not receive Hybrid Assistive Limb (HAL) treatment was used for comparison as a healthy gait
14.2 ± 5.7 steps and 10.8 ± 2.0 steps were recorded by the motion capture in 10 m walking tests before and after the HAL intervention, respectively
Summary
Myelopathy refers to a pathology that causes neurological deficits in the spinal cord (Oyinkan Marquis and Capone, 2016), that usually results from compression of the spinal cord by osteophytes or extruded intervertebral disks between the cervical spine (Seidenwurm, 2008). OPLL is a hyperostonic condition characterized by pathological ectopic ligament ossification that mostly affects the cervical or thoracic spine segments (Epstein, 2002; Matsunaga and Sakou, 2012) and commonly presents with myelopathy and radiculopathy. Even after appropriate decompression operation has been successfully achieved, patients are sometimes left with residual motor impairments. Several methods for gait rehabilitation are available for patients with myelopathy following surgical decompression including muscle training, range of motion training, movement equilibrium training, and sphincter control. Several studies have shown that there are no advantages to using passive robotic rehabilitation such as treadmill walking (Hidler et al, 2009) compared to conventional rehabilitation therapy (Dobkin et al, 2006)
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