Degenerative disc disease of the cervical spine typically develops in the aging population equally in terms of patient sex. Patients most commonly present with pain. Pain, or in combination with other neurological symptoms, may require surgical intervention. Treatment options range from nonoperative measures to decompression, instrumented fusion, or a combination of both laminoplasty or instrumentation or a combination of both. This chapter will examine the anatomy, natural history, etiology, pathophysiology, evaluation, and treatment options.
The cervical spine, C1 to C7, provide exceptional function and range of motion. The upper cervical spine, C1 (the atlas, which articulates with the occiput), and C2 (the axis) are highly specialized, allowing for significant ranges of motion (rotation, flexion, extension, and side-bending) related to facet orientation allowing for more rotation. Structures adjacent to the cervical vertebrae include the spinal cord and nerve roots, blood vessels as well as the trachea and esophagus.
The intervertebral disc (IVD) is found from the C2-C3 level down, aids in cervical spine mobility and stabilization. In contrast to the thoracic and lumbar vertebrae, the cervical vertebrae have a unique bony prominence called the uncinate process, which articulates with the adjacent level to form the joint of Luschka or uncovertebral joint. This joint helps to reinforce the IVD and provides additional stability and motion. The IVD is an intricate structure composed mainly of two parts, the peripherally located annulus fibrosus (AF) and the centrally located nucleus pulpous (NP) which are responsible for its’ load distribution function. The anterior and posterior longitudinal ligaments reinforce the IVD.
The AF of the intervertebral discs is mostly of type I collagen in layers (lamellae), proteoglycans, glycoproteins, elastic fibers, and extracellular matrix (ECM) secreting cells. These collagen layers are uniquely positioned to form a strong shell for the inner contents, the NP.
The NP has a gel-like consistency composed mainly of water, which decreases with age (~90% at birth and 70% by the age of 60). The remaining minority of the NP contents then consists of type II collagen and proteoglycans. A critical proteoglycan in the NP is aggrecan, which, when bound to hyaluronic acid, helps to keep water within the NP, allowing for load resistance.
After the first years of life, the IVD becomes the largest avascular structure in the body. Most of the nutrition delivery is via metabolite diffusion from the vertebral endplates. Over time, the IVD not only begins to lose its water content but its proteoglycan supply as well, leading to a more fibrotic consistency of the NP and subsequent fissuring As those vertebral endplates calcify with aging.
There are different types of NP herniations. If the NP herniates but remains contained by the annulus, it is referred to as a disc protrusion. However, the NP can also penetrate through injured annular fibers, and NP contents can extrude through a defect in the annulus, referred to as a disc extrusion. Furthermore, NP fragments can be separated from the extruded disc material, yielding disc sequestration.
The degenerative process of the cervical spine classifies into three distinct stages: (1) dysfunction, (2) instability, and (3) stabilization. Dysfunction occurs between the ages of 15 to 45 years old. During this stage, radial and circumferential tears can occur in the annulus accompanied by facet joint localized synovitis. Instability (2) can occur in individuals between the ages of 35 to 70 years old. This stage is characterized by disruption of the inner disc with progressive resorption, as well as facet joint degeneration. This condition leads to the final stage of the process, stabilization, occurring most commonly after 60 years of age. Here, hypertrophic bone develops around the facet joints as well as the disc, promoting stiff and possible ankylosing spine.
Interestingly, each spine segment may be at a different degenerative stage. One level could be completing the dysfunction stage while another beginning the stabilization phase. Disc herniations appear to occur as a result of dysfunction and instability phase while spinal stenosis occurs as a result of the late instability stage and early stabilization stage as a result of the bony overgrowth and disk space narrowing It is, for this reason, one may find a patient whose cervical spine segments have a combination of disc herniations and spinal stenosis at different levels.C5-6 is most commonly affected due to biomechanics of the cervical spine.
When discussing the natural history of the cervical degenerative disc disease and treatment options, symptomatic patients can experience an array of symptoms from pain intermittent or constant, along with possible neurological symptoms without pain. Patients generally receive nonoperative treatment when experiencing nonprogressive pain and/or minimal neurological issues. If surgery is necessary, it is typically elective, and it can be delayed with the hope of symptomatic improvement. However, an exception is patients diagnosed with cervical myelopathy who should have more urgent surgical treatment to avoid progression.
The proper diagnosis and treatment for spondylolytic cervical myelopathy can be extremely challenging, especially in patients with or even without ongoing axial neck pain with possible radiculopathy. One must also be aware that 20% of patients with cervical stenosis may also have lumbar stenosis. While many patients may have straightforward diagnosis with a thorough history and physical examination accompanied by confirmatory imaging modalities, there is a significant subset of patients who have pain without experiencing neurological findings (aside from possible sensory changes) and whose imaging may not easily correlate with physical exam findings. It is instances such as this in which other diagnostic modalities should support a careful history and physical examination for an accurate diagnosis. Thus, a systematic assessment is imperative to diagnose and treat these patients appropriately and adequately.