Gait in Adult Patients With Cervical Spondylotic Myelopathy

Cervical spondylotic myelopathy (CSM) is a neurologic condition resulting from spinal cord compression caused by degenerative narrowing of the cervical spinal canal. CSM is most common after the age of 50 years, but the age of onset is variable depending on the degree of congenital spinal canal narrowing. Progressive degenerative changes in the cervical spine, such as disc bulges or herniations, facet hypertrophy, ligamentum flavum thickening, and degenerative vertebral spondylolisthesis, can all contribute to progressive spinal cord compression. The end result is chronic compression of the spinal cord and/or nerve roots leading to impaired blood flow, which can result in frank damage within the spinal cord itself. CSM is characterized by a wide variety of clinical presentations, which can include neck pain, numbness or weakness in the extremities, hand clumsiness, and, classically, gait disturbances. This typically manifests as difficulty with balance, but patients with more advanced myelopathy can also develop a stiff, spastic gait.

Surgical treatment of CSM revolves around decompressing the spinal cord, either with or without concurrent fusion. Many surgical strategies have been proposed. Anterior surgical approaches include anterior cervical discectomy and fusion or anterior corpectomy and fusion. Posterior surgical approaches include laminectomy with or without fusion, or laminoplasty. The choice of surgical approach is specific to each patient based upon the extent and location of the pathology, the presence or absence of deformity or spinal instability, the sagittal alignment of the spine, the presence or absence of ossification of the posterior longitudinal ligament (OPLL), as well as other patient co-morbidity factors and surgeon preference. While there may be some debate as to when patients with radiographic cervical stenosis should undergo decompressive surgery, most surgeons would agree on surgery for patients with moderate or severe clinical myelopathy.

Altered gait is frequently seen with CSM, and has been reported to be improved by surgical intervention. A stiff or spastic gait is also characteristic of CSM in its later stages. Many clinical studies have determined that patients with CSM have a slower gait speed, prolonged double support duration, and reduced cadence compared to healthy controls.Previous studies also identified reduced knee flexion during swing in the early stages of the disease, and, in more severe cases, decreased ankle plantar flexion at the terminal stance and reduced knee flexion during loading response.

Upright stance and body stability depends on the vestibular, visual, and somatosensory systems.These systems contribute to the maintenance of postural control. The spinal cord, particularly the dorsal column, is an integral part of the somatosensory system.The dorsal columns relay the position and vibration sensations as well as play an important role in maintaining postural stability and conveying sensory information such as deep sensations to the lower limbs.When the dorsal column of the spinal cord is compressed, the functions of vibration sense, deep sensibility, and joint position sense are lost. CSM patients were found to have impaired knee proprioception when using electrogoniometer.22 A damaged spinal cord causes impaired body balance because of proprioceptive loss, and patients develop ataxia in the lower limbs.

Jean Dubousset, first introduced the concept of the cone of economy and balance (COE) in 1994. The COE refers to a stable region of standing posture. The fundamental assumption is that swaying outside one's individual cone challenges the balance mechanisms and expends critical energy. Balance is defined as the ability of the human body to maintain its center of mass within the base of support with minimal postural sway. Sway is the movement of the COM in the horizontal plane when a person is standing in a static position. Balance efficiency is defined as the ability of the patients to maintain their COM within the COE with minimal sway and energy expenditure.Maintenance of balance requires coordination between the sensorineural and musculoskeletal systems. Very few studies have looked at functional balance in CSM patients. These studies used a stabilometer to measure center of gravity. During a 30 seconds balance test with closed eyes, CSM patients swayed significantly more and had greater postural instability compared to healthy controls. Neither of those studies reported on neuromuscular activity during a functional balance test. Haddas et al.was first to introduce a method to objectively quantify the COE and neuromuscular energy expenditure during a dynamic balance test.

There is very little literature investigating the effect of surgical intervention on a CSM patient's balance and gait using human motion analysis both before and after surgery. In fact, there have not been any studies examining how surgical intervention for CSM can improve patients' balance and gait utilizing objective neuromuscular data as well as full body kinematic analysis. Additionally, none of the previous studies have been able to validate self-reported pain and functional outcome measures utilizing a human motion capture system and EMG.

This study explores the effect of CSM on human balance and gait and will utilize kinematic balance and gait analyses to examine the dynamic range of motion of the spine and lower extremities, along with neuromuscular data from surface EMG to precisely define the timing and degree of spine and lower extremity muscle activation and peak activity, as well as measurements of ground reaction forces throughout the gait cycle. All of this will be compared pre- and post-operatively and also with a healthy control group in order to determine the extent to which CSM affects the biomechanics of and neuromuscular control during balance and gait and how this changes after surgical intervention. We will also be able to correlate these objective measures with patient self-reported pain and function based on commonly used outcome instruments.

In summary, the purpose of this study is to explore the level of functional compromise, both objectively and with patient-reported outcome measures, in patients with CSM and to quantify the possible benefit of surgical intervention on the biomechanics and neuromuscular control of the spine and lower extremities as evaluated by balance and gait analyses using dynamic EMG, video motion capture, force plate analysis, and validated patient-reported outcome metrics.