Cervical spondylosis is often due to arthritic changes of facet joints, hypertrophy or buckling of the ligamentum flavum, ossification of the posterior longitudinal ligament, intervertebral disk degeneration and herniation, or osteophyte formation (1, 2, 3, 4 and 5). Typically a combination of these factors leads to cervical stenosis (Fig. 140.1). A person can, additionally, have a dynamically unstable spine leading to cervical cord compression with motion or have an underlying congenital cervical stenosis with a developmentally narrow canal, which is less tolerant of degenerative changes or trauma. Cervical spondylosis and stenosis can lead to cervical radiculopathy if a nerve root is compressed or cervical spondylotic myelopathy (CSM) if the entire spinal cord structure is compressed (4—5). The average sagittal diameter of the adult spinal cord is 10 mm (6), and a recent cadaveric study on 469 adult skeletal specimens found an average anterior-posterior canal in all specimens of 14.1 ± 1.6 mm at the midcervical spine (7). Edwards’ and LaRocca’s (6) review of 63 patients’ radiographs with degenerative spondylosis found that patients with midcervical diameters between 10 and 13 mm were premyelopathic, between 13 and 17 mm the patients were less prone to myelopathy but were prone to symptomatic cervical spondylosis, and greater than 17 mm enabled improved tolerance of the spondylotic changes. A stenotic canal can be determined by the vertebral body ratio method by dividing the sagittal diameter of the spinal canal by the sagittal diameter of the corresponding vertebral body on plain radiographs (8). A value of 0.8 or less suggests cervical stenosis with a reduced space available for the spinal cord (SAC) and an increased risk for neurologic injury with trauma (5,8, 9 and 10). However, the clinician must be cognizant that plain radiographs only depict the bony margins of cervical canal space and does not demonstrate stenosis that often occurs from soft tissue pathology such as disk herniations or ligament buckling or predict the level and degree of cervical cord compression (11). Alternatively, stenosis has also been defined as a decrease in transverse sectional area for the spinal cord on computed tomography (CT) myelography or MRI to less than 55% to 75% of its normal value (12). Others have reported an anterior-posterior compression ratio at necropsy and correlated this with extensive demyelination of the posterolateral funiculus and infarction of the gray matter (Fig. 140.2) (13). Presumably, this ratio can be also calculated on axial cuts on an MRI.

Symptoms of stenosis depend on the specific neural region or structure involved. If a cervical nerve root is
compressed, lower motor neuron dysfunction, termed radiculopathy, can present in anatomical structures innervated by the involved nerve root. This can present as pain and/or motor/sensation abnormalities of the neck, shoulder, suboccipital region, or upper extremity along with a decreased deep tendon reflex (4). However, if the cervical spinal cord is compressed, upper motor neuron dysfunction and long tract signs, termed myelopathy, may be present. The latter may present as brisk deep tendon reflexes, extensor plantar reflexes, inverted radial reflexes, Hoffman’s sign, myelopathy hand, difficulty with fine dexterity, gait and balance abnormalities, bowel/bladder dysfunction, and/or paraparesis (3,5,10,14). CSM can be due to SCI from direct mechanical injury, vascular injury and ischemia, demyelination, and neuron necrosis (2 and 3,5).