Deformity in the Cervical Spine

Background

The normal alignment of the cervical spine is lordosis. ^, The cervical spine provides a transition from the rigid thoracic spine to the cranium and supplies the ability to alter position and thereby improve the swallowing function and optimize sight. Numerous forces, both internal and external, may affect the structure and position of the cervical spine such that it becomes deformed or altered from its normal anatomic alignment. Normative values of cervical lordosis (CL) ideally result in upright, horizontal gaze and a mobile spine ( Fig. 32.1 ). However, in patients with CSD, the relationship between cervical alignment, horizontal gaze, sagittal balance, and mobility are complex and not well elucidated. In the lumbar spine, normative values of lordosis are determined relative to the patient’s pelvic incidence. Staub and colleagues were first to suggest a similar relationship between CL and T1 slope (T1S); however, it is unclear if these values can be used to determine thresholds for restoring CL in a kyphotic spine ( Fig. 32.2 ).

Degenerative cervical spondylosis is characterized by loss of intervertebral disc space height, facet and uncovertebral joint hypertrophy, osteophyte formation, ligamentum flavum redundancy and hypertrophy, and ossification of the posterior longitudinal ligament (OPLL). The combination of these changes leads to central canal and neuroforaminal stenosis causing myelopathy and/or radiculopathy. In addition, the length of the cervical spinal canal measured in the sagittal plane during flexion (kyphotic posture) is greater than during extension (lordotic posture). In some patients, these changes ultimately result in sagittal malalignment, or CSD ( Fig. 32.3 ). The most common form of CSD encountered by surgeons is kyphosis, which will be the focus of this chapter. Ruangchainikom and colleagues divided cervical kyphosis into three different radiographic subtypes based on the Ohara classification system (C-, S-, and R-types). ^, The subtypes are determined based on vertebral body displacement relative to the C2–C7 plumb line. Although the clinical significance of the subtypes is yet to be elucidated, there is evidence to suggest that reverse sigmoid kyphosis (R-type) is more likely to result in chronic spinal cord compression when the neck is in neutral position.

Kim and colleagues further defined the morphology of CSD as having three distinct patterns: flat neck, focal deformity, and cervicothoracic deformity. These subtypes were classified based on their global alignment and flexibility on flexion/extension radiographs. Similarly, Ames and colleagues proposed a novel CSD classification system that incorporates radiographic morphology, severity of myelopathy (as determined by the modified Japanese Orthopaedic Association Scale [mJOA]), and global spinopelvic alignment. Unlike the Scoliosis Research Society–Schwab classification, which has been clinically validated for thoracolumbar adult spinal deformities, a validated reference CSD classification system remains to be developed. ^,

In patients with mild myelopathy (mJOA >15), surgical intervention could be deferred in favor of structured rehabilitation. However, surgical intervention is warranted in patients with moderate to severe myelopathy (mJOA <15), patients with an inability to maintain horizontal gaze (chin-on-chest), those who experience neurological deterioration, and/or those who fail to improve with supervised rehabilitation. ^, In this chapter, we further discuss preoperative workup, surgical options, and outcomes after surgery for adult CSD.

Pathophysiology

CSD can result from numerous hereditary, systemic, neuromuscular, posttraumatic, and iatrogenic etiologies. Subaxial cervical deformities can develop in any axis but most commonly occur in the sagittal plane, primarily as a kyphotic deformity.

Congenital Cervical Scoliosis

The origin of congenital scoliosis may be environmental or genetic, or the condition may result from a combination of factors. Epigenetic factors have also been implicated in the development of vertebral abnormalities. Given the rarity of congenital cervical scoliosis, the majority of the published literature is in the form of case series/reports. For example, Ruf and colleagues described a case series of three patients treated with hemivertebra resection for congenital cervical scoliosis presenting with medically refractory torticollis. Surgery was performed by the 540-degree approach at a mean age of 9 years. Torticollis improved by 16 degrees to an average of 1 degree postoperatively and 3 degrees at long-term follow-up.

Svantesson and colleagues published a report of 320 patients in Sweden with juvenile rheumatoid arthritis and found that 5.3% presented with scoliosis predominating in the thoracic and lumbar spine, with minimal cervical involvement. More than 50% presented with a thoracolumbar scoliosis greater than 20 degrees. Torticollis was seen in three of the 17 patients and was associated with increased cervical curvature.

Common hereditary disorders that often present with scoliosis include Marfan and Klippel–Feil syndromes. The incidence of scoliosis in patients with Marfan syndrome ranges from 55% to 64% among reported case series. There is a predilection for thoracic and lumbar spine involvement, and isolated cervical scoliosis is rare. The scoliosis associated with Marfan syndrome has a clinical presentation similar to idiopathic scoliosis, with the exception of a higher prevalence of triple major and double thoracic curvatures. Shirley and colleagues noted that the presence of an adolescent curvature exceeding 40 to 50 degrees had a higher likelihood to progress into maturity, suggesting that treatment goals should be to prevent curvature of adolescence from exceeding 40 degrees. In an additional retrospective review by Jones and colleagues, 39 patients with Marfan syndrome who underwent deformity correction surgery at two institutions highlighted the technical difficulties with instrumentation and inherent comorbidity because of cardiopulmonary insufficiency. Pseudoarthrosis was noted in 10%, and there was an additional instrumentation fixation failure rate of 21%. The rate of surgical site infection was approximately 8%. The authors argued that a thorough preoperative cardiopulmonary work-up was warranted for all Marfan patients, with careful attention paid to preoperative computerized tomography scans to assess bone health and dural ectasias, if present.

Similarly, Klippel–Feil is a syndrome of abnormal spinal segmentation that results in the fusion of vertebral bodies in the cervical spine. Feil further subclassified these patients into three distinct groups. Group I included patients with fusion of cervical and upper thoracic vertebrae with synostosis. Group II included patients with congenital fusion of the vertebrae in the cervical spine only. Group III included patients with cervical vertebral fusions as well as associated lower thoracic or upper lumbar fusion. Otolaryngological, kidney, ocular, cranial, limb, and digit anomalies are often associated. Thomsen and colleagues reviewed data from 57 patients with Klippel–Feil syndrome treated over 25 years. They found that group I patients had a mean Cobb angle of 31 degrees at the level of fused cervical vertebrae. Patients in groups II and III had Cobb angles of 9 and 23 degrees, respectively. Approximately 70% of patients had concomitant thoracolumbar scoliosis.

Idiopathic Scoliosis

Adolescent idiopathic scoliosis (AIS) is the most common form of scoliosis and is a diagnosis of exclusion. AIS is defined as the presence of a coronal curvature greater than 10 degrees combined with a rotational component and no other etiological explanation in a child 9 years of age or older. If the child is younger than 9 years of age, the diagnosis is referred to as early-onset scoliosis. Historically, treatment options for AIS included exercise, inpatient rehabilitation, braces, and surgery. In a recent study by Norheim and colleagues, the association between cervical spine alignment and Lenke AIS type was closely examined in a cohort of 3654 patients. The authors found that there was significantly less cervical kyphosis in Lenke 3 and 4 curves and significant greater kyphosis in Lenke 1, 2, 5, and 6 curves. There was no significant difference in C2–C7 sagittal vertical alignment. The authors stated that these findings appeared to demonstrate that AIS patients compensate for abnormal global spinal alignment with changes in cervical sagittal alignment.