Anterior Approaches for Multilevel Cervical Spondylosis

Cervical Spondylotic Radiculopathy/Myelopathy: An Overview of Pathophysiologic Mechanisms and New Insights

For over a century, age-related loss of disc water content and disc space height reduction has been identified to be the initiating point of pathogenesis of the process of degenerative spinal disease. The disc alterations are considered to be the primary issue and the rest of the spinal bony and ligamentous consequences are secondary effects. Osteophyte formation, ligamentous hypertrophy, and secondary reduction in root and spinal canal dimensions are the events that result in root and cord compression and resultant symptoms of radiculopathy and myelopathy. Essentially the existing concept is that the symptoms are related to unwanted intrusions in the spinal or root canal that compromise their dimensions and result in compressive symptoms. The aim of the contemporary surgical treatment is to resect the spinal cord/nerve root indenting osteophytes and hypertrophied ligaments and to widen the spinal canal and root canal dimensions. A range of surgical techniques and elaborate technological tools has been in use for the surgical treatment. Despite all this, it may not be an over-exaggeration to say that there is no standard or gold standard understanding or treatment that has universal acceptance.

Although instability of the spine and spinal segments is sometimes considered in the overall pathogenesis of disease and of clinical symptoms, its numero uno position in the entire scenario of the degenerative disease has not been extensively evaluated and therapeutically exploited. Goel recently speculated that instability of the spinal segments is the primary pathogenetic phenomenon and that the remainder of the musculoskeletal and disc alterations are secondary processes.

Spinal degeneration could be a price that is paid for standing human posture and life-long strain on the muscles of the spine that position the body in an erect posture. The primary muscles that support the spine and assist in maintaining erect posture are the long multisegmental and short intersegmental extensor muscles of the spine. Each segment of the spine appears to be a discrete unit. The role of these muscles is to partake in the process of movements of the spine and support the column in erect standing posture. Weakness of the muscles is related to growing age or to their abuse or disuse over a period of time. Identification of the fact that instability of the spine is the primary event and that the rest of the so-called pathological features like disc space reduction, osteophyte formation and ligamentous hypertrophy are secondary and possibly protective in function, has the potential of revolutionizing the treatment paradigm for the entity of “spinal degeneration.”

Intervertebral disc was visualized prominently on plain radiological examination without being actually seen. Intervertebral disc, osteophytes, and cord changes are prominently visualized on computer-based imaging. This is probably the reason that the entire concept of spinal degeneration has been earlier based on disc-related issues and later on osteophytes, ligaments, and structural alterations in the cord. Due to their lateral location and oblique profile, even on modern computer-based imaging instability at the facets is difficult or impossible to decipher.

As the understanding of issues related to spinal degeneration mature, we realize that muscle weakness related facetal listhesis and vertical facetal instability are the prime issues in spinal degeneration. The facet joint has an oblique alignment in the cervical and dorsal spine and a near vertical alignment in the lumbar spine. ^, The slipping, telescoping, or listhesis of the rostral facet over the inferior facets results in all the subsequent secondary and so-called degenerative changes in the spinal segment/s. Reduction in the height of the neural foramina, circumferential buckling of all the inter-spinal ligaments, reduction in dimensions of the spinal and root canal, and reduction in the disc space height are all a part of the secondary bodily response. Osteophyte formation is circumferential around the entire rim of the spinal canal and even around the facets and is related initially to ligamentous separation from the bone surface, periosteal reaction, and subsequent osteophyte formation. Radiologically, the osteophytes are more prominently seen in relationship to the posterior longitudinal ligament. The osteophytes around the facets and around the other parts of the circumference of the spine are obvious only in the late phase of the disease process. The phenomenon of development of ossification of the posterior longitudinal ligament (OPLL) is speculated to be an advanced form of osteophyte formation and probably depends on the developmental pattern of spinal instability. Essentially, it seems that the nodal point of pathogenesis of both spondylotic degeneration and OPLL is spinal instability.

The reversal of pathological events following Goel’s facetal distraction technique provides support to such a hypothesis. ^, Specially designed “Goel facet spacers” were impacted into the intra-articular cavity after appropriate distraction of the facets. The technique was aimed at achieving distraction-arthrodesis of the affected spinal segments. The observation that the distraction of the facets resulted in an immediate postoperative reversal of all the known pathological features of degenerative spine gives credence to the hypothesis. Distraction of the facets resulted in stretch reversal of buckling of circumferential intervertebral ligaments, increase in the disc space height, and an increase in the spinal and neural canal dimensions. The proposed operation of facet distraction suggests that the disc can “regenerate” and its height can be restored and there is a potential for reduction of the size of the osteophytes. It presents an alternative hypothesis that suggests that there may not be a need for removal of the disc and osteophytes during the surgery for spinal degeneration. It also suggests that the spinal and root canal can be decompressed without removal of any segment of bone or ligament. The concept provides a fresh thought in the treatment strategy of spinal degeneration. The treatment thus changed to dealing with posteriorly located facets than an anteriorly located disc and from the surgery that was earlier aimed at decompression of neural structures to that directed at spinal fixation.

On further evaluation, it appears that it is not neural compression or deformation, but it is repeated micro-injuries to the spinal cord as a result of instability that is the cause of neurological symptoms. It was realized that more than distraction of the spinal segments, it is their stabilization that is more important for restoration of neural function and amelioration of symptoms. Accordingly, we resorted to “only fixation” as the treatment for single or multilevel spinal degeneration related radiculopathy or myelopathy. Transarticular facetal fixation was identified to be a safe and strong and rather straightforward surgical option for fixation. The oblique profile, relatively large size, and biomechanical strength of the facets can be used effectively and safely for transarticular screw insertion. In general, presence of osteophytes signals instability of the spinal segment. Presence of altered cord intensities also point toward spinal instability related effects. The therapeutic implication of the proposed concept is that the surgery in cases with spinal degeneration should be focused on treatment of spinal instability. Such spinal facetal instability is rather easily observed on direct visualization of the joint during surgery, even when preoperative dynamic radiographs do not depict such an event.

Craniovertebral junction is generally excluded from the ambit of discussion on multisegmental degenerative cervical spondylotic disease. More commonly degenerative cervical spondylotic disease is identified in the lower cervical region and the incidence of spinal involvement progressively reduces in higher segments and the discussion generally does not involve the spine above C2-3 level. Although instability of the subaxial facets is difficult to evaluate radiologically due to their oblique profile, atlantoaxial facetal instability is relatively easy to decipher due to their brick over brick rectangular configuration. Our studies conclude that atlantoaxial joint, which is the most mobile joint of the body, is most likely to develop instability. An alternative classification divided atlantoaxial dislocation on the basis of facetal malalignment and identification of instability on direct bone manipulation during surgery. Atlantoaxial instability in absence of abnormality of atlantodental interval and direct compression of neural structures by the odontoid process was labeled as central or axial atlantoaxial dislocation. In such a form of instability the facet of the atlas is dislocated posterior to the facet of the axis in the neutral head position (type 2 atlantoaxial facetal dislocation) or the facets of atlas and axis are in alignment but the dislocation or instability is identified by direct bone handling or manipulation during surgery (type 3 atlantoaxial facetal instability). As neural compression is not an early or a prominent feature, the symptoms are chronic and long-standing in nature. Central or axial atlantoaxial instability is associated with chronic degenerative spinal changes that manifest as multiple level spondylosis. On the other hand, type 1 facetal instability, where on lateral profile imaging the facet of atlas is dislocated anterior to the facet of axis, the symptoms are relatively acute as there is abnormal alteration in the atlantodental interval and compression of the spinal cord by the odontoid process. Type 1 facetal instability is less frequently associated with chronic pathological entities like degeneration-related spinal disorders. It appears that atlantoaxial instability could be a primary pathology that leads to secondary degenerative changes in the cervical spine or it may be associated with multilevel spinal instability. Identification of atlantoaxial instability and subaxial multilevel spinal instability and stabilization may form a rational form of treatment for multilevel spinal degeneration. The exact indication of inclusion of atlantoaxial joint in the fixation construct will have to be evaluated by further clinical studies.

Conventionally and historically, anterior cervical approaches have been popularly employed for the treatment of cervical degenerative spondylotic disease. The abnormality of the disc bulge and osteophytes are manifested anterior to the cord. Relieving the cord of the compressive effects of the disc protrusions and indenting osteophytes and stabilization of the treated spinal segments is the general aim of surgery. As certain degree of disc bulges are almost always seen in the elderly, it is crucial to clinically correlate the radiological observations. It must be remembered that surgery is not performed to mend the radiologic image, but rather it is done to treat the patient’s symptoms. Surgical decisions based on clinical presenting features are important in general, but they are critical in patients with multilevel cervical spondylotic myelopathy (CSM).

Single-level disc prolapse occurs in relatively younger individuals. The symptoms are acute and in the form of radiculopathy. A sudden excessive physical movement results in injury to the annulus fibrosus and herniation of nucleus pulposus through the rent thus created. Essentially, the injured disc loses its turgor and the involved spinal segment becomes potentially unstable. The disc is “soft” in such cases. More often, lower cervical discs are involved in herniation. Severe pain, persistent numbness or weakness in the distribution of the nerve, and progression of symptoms can indicate the need for surgery. If the symptoms are tolerable and stable or improving, a conservative observation can be advised. A cervical collar can be useful in such a situation. Resorption of the herniated part of the disc over a period of time is the rule, and there can be progressive improvement in the symptoms. Long-term outcome of a non-operated disc herniation is resorption of the herniated and contained disc components and fusion of the vertebral bodies. In general, surgery for symptom of radiculopathy needs to be carefully selected and intensity and nature of progression of symptoms dictate the indication. We have recently identified that more than direct root compression by the herniated disc, it is instability of the spinal segment that is responsible for the symptoms of radiculopathy. Relief of pain by neck immobilization by external arthrodesis or by traction are suggestive of the relevance of instability as the primary source of symptoms.

Multiple-level compression of the spinal cord by spondylotic bars forms an entirely different pathologic entity. The affected patient is usually in an older age group. The symptoms are relatively subtle, slowly progressive, and long-standing. The symptoms are usually of pain and myelopathy. The disc is hard and is mainly in the form of multiple osteophytic bars. The use of a cervical collar or restriction of neck movements has a limited and probably a negative role in the management of these patients. Selection of the correct case for surgery is crucial in such cases. Presence and progression of symptom of myelopathy indicates the need for surgery.

Diagnosis of Cervical Spondylotic Radiculopathy/Myelopathy

Anterior Surgery for Multilevel Cervical Spondylosis

If appropriately selected, surgery for MCS is a rewarding operation. Although the need for decompression of the cord from the osteophytic compression is necessary, the indication and methodology for fixation is a debated subject. Wide decompression of the cord by removal of the osteophytic bars should be the aim. The need to remove the vertebral bodies or to perform a corpectomy to remove the osteophytic bars is also a debated subject. However, the relative ease of performance of decompression by performing corpectomy has led several authors to recommend such an operative approach.

With the advent of anterior cervical spinal surgery after its original description by Smith and Robertson and Cloward over 50 years ago, the possibility of treatment solutions for the cervical spine have immensely expanded. It became possible to treat more complex pathologies from the front. ^, Being able to access the anterior column of the cervical spine enables the surgeon not only to create a biodynamically sound construct in case anterior support is disrupted or lost but also to address a narrowed cervical spinal canal from the aspect where the majority of compressive phenomena originate, which is anteriorly. This is particularly true in the majority of cases of CSM, where anterior compression can be due to herniated discs, osteophytes of the posterior vertebral margins, or OPLLs. The anterior approach has therefore become the favorite route for surgery on single- or multiple-level cervical spondylotic myelopathy. ^, to

Although the author is personally treating all cases of multilevel cervical spondylotic myelopathy with only a posterior surgical multilevel fixation without resorting to any kind of bone or soft tissue decompression, anterior cervical decompression-fixation surgical approach is still a more popular form of surgical treatment. The continued popularity of anterior cervical surgery seems to be attributable mainly to two facts: (1) As mentioned earlier, the majority of compression in MCS lies anteriorly in the spinal canal, and (2) the surgical steps and instrumentation are standardized and most publications favor the anterior surgical route. The kyphosing potential of multilevel laminectomy without fusion is also a discussed issue. However, such an issue is more relevant in younger patients operated for tumor pathology. ^,

In the following section, the various techniques available to address CSM via the anterior approach are discussed.