Cervical Spine Deformity

Indications, Considerations, and Surgical Outcomes

Samuel K. Cho, MD; Scott Safir, MD; Joseph M. Lombardi, MD; Jun S. Kim, MD

Disclosures

J Am Acad Orthop Surg. 2019;27(12):e555-e567. 

In This Article

Etiology

Congenital

Atlanto-occipital fusion, os odontoideum, and basilar invagination are atlas and axis anomalies that can lead to CSD. Klippel-Feil syndrome, which causes most of the subaxial cervical congenital defects, involves fusion of cervical vertebrae (Figure 1). Achondroplasia, the common skeletal dysplasia, can lead to posterior vertebral scalloping, short pedicle canal stenosis, laminar thickening, and widening of intervertebral disks. Down syndrome is linked to ligamentous laxity that causes cervical instability seen at both the atlanto-axial joint and occiput-C1 level.

Figure 1.

A, Preoperative AP and lateral radiographs of the cervical spine demonstrating kyphoscoliosis in an adult patient with Klippel-Feil syndrome. B, MRI of the cervical spine showing stenosis. C, Postoperative AP and lateral radiographs of the cervical spine after C2-T3 circumferential reconstruction.

Traumatic

CSD can result from instability secondary to trauma. Upper CS injuries include occipitocervical dislocation, occipital condyle fractures, atlas fractures, atlanto-axial rotatory instability (AAI), atlanto-dens instability, and odontoid fractures. Subaxial injuries include traumatic spondylolisthesis of axis (Hangman's fracture), flexion injuries, vertical compression injuries, and subaxial extension injuries. Posttraumatic CSD develops in most patients because of the trauma itself, but interestingly, a minority of patients in whom a posttraumatic CSD develops do so because of nonunion, implant failure, Charcot joint, or technical error after surgery for the injury.[1] Injuries involving the posterior ligamentous structures, such as advanced-staged burst flexion-compression or flexion-distraction injuries, are prone to deformity overall (Figure 2), whereas lateral compression or burst injuries can result in posttraumatic coronal or scoliotic deformities.[1]

Figure 2.

Chronic flexion-distraction injury leading to angular kyphotic deformity in the subaxial cervical spine. This patient successfully underwent C2-T1 circumferential spinal fusion with correction of deformity.

Spondylosis and Degenerative Disk Disease

Disk degeneration leads to increased mechanical stress at the cartilaginous end plates at the vertebral body (VB) lip. Generally, spondylosis begins with intervertebral disk desiccation, leading to bulging of the anulus fibrosus, loss of height anteriorly, and a positive feedback loop of increased anterior weight bearing leading to cervical kyphosis (CK)[2] (Figure 3). Spondylosis is also associated with ossification of the posterior longitudinal ligament, which can contribute to ventral cord compression. This often leads to loss of lordosis in the subaxial spine and can negatively influence global sagittal alignment (GSA). Patients will often hyperextend through their high CS (occiput-C2) to compensate for the loss of subaxial segments. By contrast, pure scoliotic deformity is rarely from spondylosis.

Figure 3.

An adult patient with severe spondylotic kyphosis (A). He is hyperlordosing his lumbar spine to maintain horizontal gaze. C2-T4 posterior spinal fusion with C7 pedicle subtraction osteotomy to correct the deformity (B).

Inflammatory

Rheumatoid arthritis (RA) is the most common inflammatory disorder that can affect the CS. The prevalence of CS involvement in RA ranges from 25% to 80%, depending on the algorithm used,[3] with seropositivity as a major risk factor. The three typical RA deformities in the CS are, in order of decreasing frequency, AAI or subluxation, superior migration of the odontoid process, and subaxial subluxation.

Seronegative spondyloarthropathies include ankylosing spondylitis (AS), Reiter's syndrome, psoriatic arthritis, and enteropathic arthritis. AS is the most common of the seronegative disorders and will affect the CS later in the disease course. Common manifestations in the CS are CK and AAI. Global spinal kyphosis progresses as a means to offload painful facet joints, and autofusion in this abnormal sagittal alignment leads to a fixed flexion deformity. Furthermore, susceptibility to spinal fractures leads to frequent and missed fractures that can worsen the existing deformity.

Iatrogenic

Iatrogenic (postoperative) remains the most common cause. Typically, postoperative CK is associated with a previous laminectomy or laminoplasty and demonstrates a loss of sagittal alignment, shifting the weight-bearing axis anteriorly (Figure 4). Surgery denervates the posterior cervical muscles, causing atrophy, and disruption of facet joints may lead to instability. Removal of the posterior tension band leads to worsening compressive forces on the anterior VB, thus exacerbating sagittal deformity and causing a kyphotic angulation.[4]

Figure 4.

Post-laminectomy kyphosis. Patient required a long spinal fusion (C2-T1) to correct the deformity.

The incidence of iatrogenic CSD is difficult to measure because of heterogeneity of patient and case complexity. One case series demonstrated a 45% incidence in patients without any preoperative instability.[5] Contrarily, postoperative kyphosis developed in 10.6% of patients undergoing laminoplasty for cervical spondylosis, ossification of the posterior longitudinal ligament, and multilevel disk herniation.[6] A retrospective analysis investigating the incidence and outcomes of kyphotic deformity after laminectomy for cervical spondylotic myelopathy determined that kyphosis may develop in 21% of these patients.[7] In the pediatric population, weaker musculature, ligamentous elasticity, and greater horizontal facets have been theorized to account for the greater rates of postoperative kyphosis.[8]

Postoperative development of instability because of removal of static and dynamic stabilizing soft-tissue structures and facet violation is a well-known complication, and it was a major stimulus to the use of laminectomy with instrumented fusion and laminoplasty. The literature comparing outcomes of laminoplasty versus laminectomy are disparate, likely secondary to the heterogeneity between surgeon technique and patient as well as radiographic characteristics.[9,10] It can be agreed on, however, that the progression of loss of lordosis to kyphosis after laminoplasty appears to be dependent on the technique. Invariably, the preservation of muscle attachments has been shown to be essential for maintaining sagittal cervical alignment. The posterior cervical approach requires careful exposure from C3 to C7 while taking care to dissect in the avascular plane, or the raphe, between the left and the right paraspinal musculature. Additionally, during exposure of the lateral masses, facet capsule violation can lead to accelerated spondylosis, axial neck pain, and loss of lordosis.

Infectious

Though a small contributor to the overall causes of CSD, spinal infections represent a growing area, given the use of illicit intravenous drugs in the younger population and genitourinary surgery and intravenous access devices in the elderly. Infections may involve any part of the spine including the VB, intervertebral disk, neural arch, or posterior elements, but most commonly it will affect the anterior and middle columns. Given its rich vascular supply, the VB are a common destination for dissemination of hematogenous osteomyelitis. Kyphosis is often a late finding but can present more frequently if Mycobacterium tuberculosis is the etiologic agent. In addition, early surgery for vertebral osteomyelitis has the benefit of improving stability and reducing kyphotic deformity relative to conservative management. Patients being treated with chemotherapy for spinal tuberculosis have, on average, an increase of 15° in deformity, and a kyphosis of >60° develops in 3% to 5% of patients.[11]

Neoplastic

Though tumors involving the spinal cord or surrounding structures in the CS are much more likely to cause deformity via the therapeutic approach used to manage them, certain entities exist which may engender malalignment and deformity even preoperatively. Kawabata et al[12] described their experience treating three patients with severe CK associated with neurofibromatosis (NF) and noted that a high risk of spinal cord injury, coexisting spinal cord and paraspinal tumors, difficulties in placing anchors in dystrophic vertebrae, and difficulty in obtaining solid fusion all potentially complicate the treatment of their patients' cervical disease.

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