The etiology of cervical spondylosis is underlying spontaneous joint degeneration. It is related to age and to wear and tear. However, concordant twin studies note a significant genetic predisposition to development of cervical degeneration, in addition to occupational and activity-related factors. Likewise, there appears to be a significant genetic or inherited predisposition to development of degenerative cervical myelopathy (DCM).
Once the degeneration begins (typically in the second or third decade), cervical joint degeneration slowly worsens over the lifetime. The relative roles of daily wear and tear, trauma, and genetics on the rate of degeneration remain unclear, although radiographic spondylosis is generally age related and no known treatments can reverse the process.
The spine includes two basic cartilaginous joints: the disk, which initially contains a complex hydrogel material, and the facet joints, which are synovial joints.
The disk hydrogel is poorly maintained with maturity due to the loss of the primary disk cells (which produce and maintain the hydrogel) and sclerosis of the end plates (preventing diffusion of nutrients). The disk joint becomes dehydrated and narrows. At a certain degree of narrowing, the annulus of the disk, which normally lacks nerve endings, can become innervated and develop osteophytes at the margins, similar to any type of mobile joint. Because the function of the facet joints is primarily prevention of rotation and flexion/extension, their degeneration is enhanced with more axial loading as the disk joint narrows, placing more stress on the facet joints.
However, a number of patients experience axial neck pain with mild degenerative changes (i.e., limited joint narrowing only). For this reason, the degree of spondylosis on cervical radiographs or magnetic resonance imaging (MRI) does not necessarily correlate with the syndrome of axial neck pain. Idiopathic axial neck pain, such as that occurring with degenerative changes, demonstrates a poorer outcome than that associated with a specific cause.
Pain in people with cervical spondylosis is thought to arise from joint receptor signals (including those of abnormal nerve fibers innervating the annulus with degeneration), which are routed to cervical paraspinal muscles in particular, resulting in paraspinal muscle spasm and characteristic interscapular and lateral neck pain.
Cervical spondylotic radiculopathy (CSR) results if the nerve exiting the spinal cord and the spinal canal is pinched by either a degenerative disk (i.e., a herniated disk, wherein an annular weak spot allows displacement of disk nucleus contents to be adjacent to the nerve root) or with moderate to severe degenerative joint changes, narrowing the root exit at the foraminal level.
DCM usually involves severe disk and facet degeneration with changes in the alignment of the spine, such as kyphosis or spondylolisthesis, along with osteophyte formation. These lead to a significantly narrowed spinal canal and secondary spinal cord deformation.
There is no simple, accepted etiologic classification, but symptoms cluster into clinical syndromes.
Axial neck pain, which includes reduced motion of the cervical spine, paraspinal muscle spasm, and referred pain, similar to other joints of the body
Cervical spondylotic radiculopathy (CSR), a specific syndrome of radiating arm pain following a single cervical nerve root distribution that arises from mechanical compression and/or chemical irritation of that specific nerve root, usually at its exit from the spinal canal
Degenerative cervical myelopathy (DCM), a specific syndrome of neurologic deficit in the upper and lower extremities resulting from spinal cord pressure in the cervical spine, due to degenerative changes in disk and/or facet joints.
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