The aetiology 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.  Similarly, there appears to be a significant genetic or inherited predisposition to development of cervical spondylotic myelopathy. 
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 2 basic cartilaginous joints: the disc, which initially contains a complex hydrogel material, and the facet joints, which are synovial joints. 
The disc hydrogel is poorly maintained with maturity due to the loss of the primary disc cells (which maintain the hydrogel) and sclerosis of the end plates (preventing diffusion of nutrients). The disc joint becomes dehydrated and narrows. At a certain degree of narrowing, the annulus of the disc, which is normally without 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 disc 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 MRI does not necessarily correlate with the syndrome of axial neck pain.    The perception of the pattern of pain with cervical spondylosis is that the joint receptor signals (including those of abnormal nerve fibres innervating the annulus with degeneration) are routed to cervical paraspinal muscles in particular, resulting in paraspinal muscle spasm and characteristic interscapular and lateral neck pain.    Idiopathic axial neck pain, such as that occurring with degenerative changes, demonstrates a poorer outcome than that associated with a specific cause. 
Cervical spondylotic radiculopathy (CSR) results if the nerve exiting the spinal cord and the spinal canal is pinched by either disc degeneration alone (i.e., herniated disc, wherein an annular weak spot allows displacement of disc nucleus contents to be adjacent to the nerve root) or with moderate to severe degenerative changes, narrowing the root exit at the foraminal level.  
Cervical spondylotic myelopathy (CSM) usually involves severe disc 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 aetiological 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
Cervical spondylotic myelopathy (CSM), a specific syndrome of neurological deficit in the upper and lower extremities resulting from spinal cord pressure in the cervical spine, due to degenerative changes in disc and/or facet joints.
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