Abstract
Background
Cervical radiculopathy is most often related to foraminal stenosis due to osteoarthritic changes of the uncovertebral joints anteriorly or zygapophyseal joints posteriorly, rather than disc herniation.
Objectives
To describe anatomical specificities of the degenerated cervical spine.
Methods
A critical narrative review was conducted. Articles were non-systematically selected and based on authors’ expertise, self-knowledge, and reflective practice.
Results
Vertebral bodies of the lower cervical spine are characterized by 2 lateral prismatic bony protuberances, the uncinate processes, located on C3 to C7 superior vertebral endplates, that are involved in the stabilization of the cervical spine. Degenerative changes at the lower cervical spine can affect different anatomical structures: the intervertebral disc, uncovertebral joints, and facet joints. The incidence and severity of changes increase with age. Furthermore, uncovertebral osteoarthritis is characterized by the presence of transverse fissures in the annulus fibrosus .
Discussion
These specific anatomical features of the cervical spine may have clinical implications, including more targeted spinal injections for managing disabling persistent or recurrent symptoms related to cervical spine degenerative changes such as cervical radicular pain.
1
Introduction
Vertebral bodies of the lower cervical spine are characterized by two lateral prismatic bony prominences, the uncinate processes (UPs), located on C3 to C7 superior vertebral endplates, that are involved in the stabilization of the cervical spine . These UPs have a biomechanical role in the kinematics of the cervical spine and can be affected by specific lesions. Degenerative changes occurring at the cervical spine can affect different anatomical structures: the intervertebral disc (IVD), the uncovertebral joints (uncarthrosis), and the facet joints . The incidence of such changes increases with age. Cervical radiculopathy is frequently secondary to osteoarthritic changes of the uncovertebral joints anteriorly or zygapophyseal joints posteriorly rather than IVD degenerative disease. Furthermore, uncovertebral osteoarthritis is characterized by transverse fissures in the annulus fibrosus .
This critical narrative review briefly outlines specific anatomical features of the degenerated anterior lower cervical spine that may have clinical implications.
2
Methods
This was a critical narrative review. Lesions of the posterior arc of the cervical spine are not detailed. The process of article selection was non systematic, because available studies on the topic are too heterogeneous to draw definitive quantitative conclusions. Therefore, the articles included were selected based on authors’ expertise, self-knowledge, and reflective practice.
2
Methods
This was a critical narrative review. Lesions of the posterior arc of the cervical spine are not detailed. The process of article selection was non systematic, because available studies on the topic are too heterogeneous to draw definitive quantitative conclusions. Therefore, the articles included were selected based on authors’ expertise, self-knowledge, and reflective practice.
3
Results
3.1
Anatomy and biomechanics of the cervical spine
The cervical spine is characterized by high multidirectional mobility for the organs of the senses. The cervical spine is classically divided into two entities: upper (from C0 to C2) and lower (from C3 to C7).
The upper cervical spine consists of atypical joints ( Fig. 1 ). The atlanto-occipital joint without IVD is not concordant or congruent. This particular anatomy allows for the passage and protection of the central nervous system. The dens of C2 articulates with the anterior arch of the atlas, forming the atlanto-axial joint that promotes rotation movements in the horizontal plane; convexity of the articular surface of the dens also allows flexion-extension movements of low amplitude. Upper cervical spine mobility allows for a combination of 3D movements while maintaining the horizontality of the look, with 40° for flexion-extension range, 5° to 10° unilateral tilt and approximately 30° unilateral rotation .
The lower cervical spine consists of large, flattened vertebrae separated by IVDs that are thicker than at lumbar level and cuneiform . IVD thickness, facet joint obliquity and capsule posterior laxity favor mobility . In addition, lower cervical spine vertebrae are characterized by the presence of bony prominences, the UPs, located on the posterolateral edge of the upper plates of the vertebrae. The UP anatomy varies among individuals and vertebral levels . The UPs have a shovel-like form and move from a lateral position to a dorsal position, from the upper to lower cervical spine region . The angle (in the frontal plane) between the posterior edge of the vertebral body and the UPs increases from C3 to C7 . The height of the UPs decreases at the lowest-level cervical spine, but their length increases from C3 to C6 . These anatomical variations affect the biomechanical properties of the uncus .
UPs have a role in stabilizing the cervical spine. They serve as rails guiding flexion-extension movements and limiting lateral tilt and posterior translation . In addition, they are involved in the automatic coupling movements of tilt and rotation of the lower cervical spine . The relationship between the IVD and UPs is complex. UPs limit the horizontal and transverse deformation of the IVD annulus fibrosus . Mechanical stress affecting UPs is greater with reduced IVD thickness .
3.2
Imaging of degenerative cervical changes
The incidence of degenerative cervical change increases with age. However, only a small proportion of patients report painful symptoms, namely cervical pain or radicular pain . Degenerative changes of the cervical spine are frequent in asymptomatic subjects. Using X-ray imaging, Friedenberg et al. found degenerative changes in 25% and 75% of asymptomatic individuals between 50 and 60 years and over 70 years old, respectively. Degenerative changes most frequently involved C5-C6 and C6-C7 levels. IVD-space narrowing was more frequent in symptomatic individuals . In an MRI study of 100 asymptomatic individuals, cervical disc protrusions were found in 20% and 57% of patients between 45 and 54 years and over 64 years old, respectively . Consistently, using MRI, Boden et al. found changes involving the cervical spine in 19% of an asymptomatic population, including patients with disc herniation or foraminal stenosis . The overall prevalence of IVD-space narrowing, IVD degeneration and osteophytes was 25% and 60% among patients under 40 years and over 60 years old, respectively . In another MRI series, changes of the cervical spine were found in 62% of patients over 40 years old and no lesions in patients under 30 .
In symptomatic patients, results of cross-sectional studies are inconsistent, and a correlation between detected degenerative changes and neck symptoms has not been clearly established . Peterson et al. did not find any significant correlation between symptoms (cervical pain and functional impairment) and severity of degenerative cervical changes detected by X-ray. However, the authors found a weak correlation between reported pain intensity and the severity of IVD degenerative disease . In the only available longitudinal study of 159 asymptomatic patients followed up for 10 years, Gore et al. confirmed that the incidence of cervical degenerative changes increased with age. During the 10-year follow-up, 24 participants (15%) showed neck symptoms, 57 (35.8%) with no radiological changes at baseline showed new lesions, and 70 patients (97%) with radiological changes at baseline showed a worsening of lesions. Only the presence of C6-C7 changes at baseline was associated with increased pain during follow-up ( P = 0.0037) .
Altogether, clinical data suggest that in some patients with disabling neck pain, symptoms seem to be related to degenerative cervical changes . Their specificity remains to be further assessed.
3.3
Cervical spine degenerative changes
Degenerative changes occurring at the cervical spine can affect different anatomical structures: the IVD, uncovertebral joints (uncarthrosis), and facet joints .
3.3.1
Degenerative IVD disease
With aging, IVDs dehydrate, splinter, crack, collapse, and decrease in height, ultimately leading to IVD protrusion or herniation in the peripheral part of the annulus fibrosus . According to some authors, this process may first involve the nucleus pulposus , then reach annulus fibrosus central and lateral fibers . IVD degenerative disease can induce changes in mechanical loading on cartilaginous endplates and UPs. Subperiosteal ossifications may then form osteophytic bars that can extend to the ventral side of the spinal canal and lead to cervical spondylotic myelopathy. Cervical degenerative myelopathy is more likely to develop in patients with a congenital narrow spinal canal (0–13 mm). Other anatomical factors can also promote cervical canal narrowing and include ligamentum flavum hypertrophy, degenerative cervical kyphosis, and degenerative spondylolisthesis . The IVD is little innervated except at its periphery. Thus, annulus fibrosus changes are assumed to be the main source of degenerative IVD disease-related neck pain.
In the early stages of degenerative IVD disease, discography is more sensitive and specific than MRI to reveal ruptures in the annulus fibrosus . However, this invasive technique is becoming less used . In more advanced stages, IVD lesions such IVD-space narrowing, peridiscal osteophyte and condensation of adjacent endplates can be detected by X-ray and MRI ( Fig. 2 ). More recently, abnormal vertebral endplate MRI signals, known as Modic changes, adjacent to degenerative IVD disease and similar to those affecting the lumbar spine, have been described . Using MRI, Man et al. found a prevalence of 40.4% (patient mean age 61.7 years) with Modic 1 and 2 signals, most frequently detected at C5/C6 and C6/C levels, with Modic 2 changes more frequent than Modic 1 changes ( Fig. 3 ).
3.3.2
Uncarthrosis
The UPs are located solely at the cervical level. For some authors, they constitute real “uncovertebral joints” including a joint cavity, cartilage lining and capsule that communicate with the IVD peripheral part . The IVD is located in the center of the endplate, but uncovertebral joints are located on each side of the endplate. In adulthood, communication between the IVD and uncovertebral joints develops through fissures in the peripheral part of the annulus fibrosus . Indeed, during disc degeneration, a bilateral transverse disc cleavage appears, originating from the peripheral lamellae of the annulus fibrosus , and develops from the UPs toward the midline . The IVD is divided in a transverse plane, from one UP to another, resulting in the formation of a neodiarthrodial joint. Uncarthrosis radiological manifestations are similar to those of peripheral joint osteoarthritis and include cartilage ulcers, cartilage thinning and the formation of osteophytes that grow laterally and posteriorly and can induce a conflict with the nerve root and in the ventral lateral region of the intervertebral foramen ( Figs. 4 and 5 ) . The most common cause of cervical radiculopathy (70% to 75% of cases) is a conflict in the foramen, narrowed by a combination of anterior and posterior osteoarthritis changes . In contrast to the lumbar spine, in cervical radiculopathy, disc herniation is responsible for only 20% to 25% of cases .
4
Discussion: management of cervical spine degenerative changes
Specific anatomical features of the cervical spine may have some clinical implications, including more targeted treatment for the management of symptoms related to cervical spine degenerative change such as disabling persistent or recurrent cervical pain and radicular pain. In this condition, after failure of well-conducted first-line treatments, including analgesics, non-steroidal anti-inflammatory drugs, oral corticosteroids and physical exercises, spinal injections are available as second-line treatments and can be discussed as a therapeutic option. We review the risk/benefits ratio for each available injection route.
4.1
Efficacy
A Cochrane systematic review of 36 randomized trials published between 1966 and 2006 evaluated the effects of pharmacological treatments for degenerative cervical spine . Only one study compared the efficacy of epidural methylprednisolone and lidocaine injections and intramuscular injections in 50 people with cervical radiculopathy secondary to cervical spondylosis . Pain and function were significantly improved at 1 month and 1 year with epidural injections (pain: standardized mean difference −1.46 [95% CI: −2.16–−0.76]; function: 0.49 [95% CI: 0.29–0.82]). Another systematic review of 7 studies with results published between 1966 and 2011 assessed the efficacy of epidural injections with or without steroids in cervical radiculopathy and chronic neck pain of discogenic, osteoarthritic or post-surgical origin. Epidural injections of combined corticosteroids and anesthetics were efficacious for neck pain and cervical radiculopathy by disc herniation but only fair with anesthetics alone. The efficacy of epidural injections with or without corticosteroids in uncarthrosis, cervical stenosis and post-surgical neck pain was fair . The largest observational study ( n = 140) evaluated the efficacy of 3 transforaminal injections of corticosteroids within 3 weeks in patients with cervical radiculopathy secondary to degenerative foraminal narrowing and 50% reduction in pain after selective transforaminal block test of the nerve root. At 14 weeks after the first injection, radicular pain was reduced (≥ 50%) in 49% of patients . However, because of the risks associated with these epidural injections, the risk/benefit balance should be evaluated for each patient.
On the basis of the anatomical specificities of the cervical spine, some authors assessed the efficacy of intradiscal corticosteroid injections to treat disabling uncarthrosis-related neck symptoms after failure of well-conducted current treatments (including a completed medical treatment and cervical epidural or facet joint infiltrations). By the intradiscal route, corticosteroids are able to reach the root conflict in the foramen in treating joint inflammation and without the risks of foraminal infiltrations . In an open-label study evaluating intradiscal infiltration efficacy of 25 mg hydrocortancyl in 20 patients with chronic disabling cervical radiculopathy related to uncarthrosis conflict without disc herniation, radicular pain was significantly decreased within 48 hours after injection and was maintained at 1, 3, and 6 months. All discographies performed during infiltration showed a transversal complete cleft of IVD. In 12 of 20 cases, a cyst-like image was found at the uncus, at the same side of the radiculopathy, suggesting a synovial cyst ( Fig. 6 ) .
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