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Cervical and Cervicothoracic Deformity Correction: Posterior-Based Osteotomies


Summary of Key Points

  • Moderate to severe adult cervical deformity has a significant impact on disability and quality of life.

  • Surgical correction of cervical spine deformities can be technically challenging, especially for rigid cases.

  • Correction of adult cervical deformity improves quality of life and can be effectively and safely performed with careful surgical planning and experience.

  • Corrective surgical strategies should consider a variety of factors related to the specific type of deformity and surgical goals.

  • Posterior-based osteotomies are essential in the correction of rigid cervical deformities.

  • Smith-Petersen osteotomies have an important role in the correction of deformities involving the subaxial cervical region, especially when combined with an anterior osteotomy.

  • Pedicle subtraction osteotomies can be technically challenging and associated with slightly higher risk of complication, but are warranted for severe rigid deformities, especially when they involve the cervicothoracic junction (patients with high T1 slope).

  • Location of the lower instrumented vertebra may play a role in the risk of distal junctional kyphosis and failure.

Whereas each region of the spinal column has unique anatomical features corresponding to its respective physiological function, the cervical spine is often regarded as the most complex. This complexity allows for the cervical spine to accommodate a wide range of motions, as well as maintain a neutral head position and horizontal gaze. The complex nature of the cervical spine makes it more prone to degeneration, arthritis, and neurological compromise––which can subsequently lead to significant disability and severe neurological dysfunction. Given the critical role of the cervical spine in normal daily function, in severe cases disability associated with cervical spine disease has been shown to be equivalent to chronic medical comorbidities, such as blindness, renal failure, and stroke. The purpose of this chapter is to review the evaluation and operative management of adult cervical deformity (ACD).

Although ACD can have variable pathological presentation in patients, the majority of ACD cases are sagittal plane deformities, with kyphosis being the most common. In addition, because isolated cervical scoliosis is a rare entity, there exists a subset of patients who present with concurrent kyphoscoliosis, generally manifested as rigid scoliosis with simultaneous sagittal imbalance. The most common etiologies of ACD include: remote traumatic injuries, inflammatory spondyloarthropathies, degenerative disc disease, myopathies, and iatrogenic causes (e.g., postlaminectomy kyphosis). ,

Cervical myelopathy, although typically thought to be associated with stenosis and spondylosis, is also commonly seen in ACD patients. Cervical sagittal deformity and kyphosis leads to increased intramedullary pressure attributed to spinal cord flattening and tension, resulting in spinal cord ischemia and neuronal injury. The impingement of the spinal cord by the vertebral body seen in cervical kyphosis can directly compress the corticospinal tract and further contribute to high intramedullary pressures. , This impingement has been demonstrated in patients with cervical spine sagittal malalignment during flexion-extension studies using a combination of magnetic resonance imaging (MRI) and electrophysiology.

As a result of their cervical spine deformities, ACD patients can experience difficulty maintaining horizontal gaze, impaired gait, and dysphagia, potentially leading to the inability to perform activities of daily living (ADLs). Secondary to this symptomology, studies have shown that increasing severity of ACD is associated with reduced health-related quality of life (HRQOL) scores. This is likely more pronounced than what is currently demonstrated in the literature, as there is a need for an ACD-specific questionnaire that can fully capture the limitations the ACD patients experience. ,

Despite the significant disabilities associated with ACD, surgical intervention has been shown to achieve excellent radiographic correction, as well as symptomatic relief. However, surgical correction of ACD presents numerous technical challenges, given the complex anatomy of the cervical spine. There are a variety of surgical treatment strategies available for cervical deformity correction, including posterior, anterior, and combined anterior-posterior approaches. The optimal surgical strategy varies from patient to patient and depends on a number of factors related to deformity type, rigidity, imbalance, and goals of surgery. In rigid, inflexible cases, soft tissue releases and osteotomies are warranted. The extent of cervical spine release and osteotomy grade has been classified by Ames et al. as the Ames Cervical Osteotomy Grade. The Ames Cervical Osteotomy Grade ranges from low-grade anterior column release and osteotomies to Smith-Petersen osteotomies (SPOs), posterior-based three-column osteotomies via pedicle subtraction osteotomy (PSO), and combined anterior-posterior vertebral column resection (VCR). Careful consideration of patient parameters during the preoperative evaluation can help determine the optimal surgical treatment strategy warranted for each specific case.

Preoperative Evaluation

Preoperative evaluation of all ACD patients should begin with a thorough history and neurological examination. In patients with severe ACD, specific questions regarding nutrition and dysphagia are important, as these are common comorbidities that can develop secondary to cervical deformity. During the physical examination, it is essential to evaluate patients standing upright, with their head and neck in maximal extension, as well as in the position that is most comfortable. The comfortable position is often more indicative of the true extent of cervical kyphosis and cervical sagittal imbalance. In addition to a physical assessment of the patient, imaging techniques such as standing scoliosis x-rays are needed to evaluate both regional and global spinal alignment. Dynamic flexion-extension x-rays should also be obtained to help evaluate rigidity and presence of spondylolisthesis. Computed tomography (CT) and MRI can be used to further evaluate bony anatomy, the presence of fusion, and compression of the nerve roots and spinal cord.

Cervical Alignment Parameters and Quality of Life Outcomes

Outcomes following cervical deformity correction surgery can be assessed in numerous ways, including through the use of radiographic measurements and HRQOL scores. The amount of HRQOL benefit provided by a given degree of correction should be considered when determining postoperative alignment goals. Postoperative cervical sagittal vertical axis (C2 SVA) and neutral chin brow vertical angle (CBVA) are two radiographic measures that have been closely associated with improvements in ADL and HRQOL outcomes. C2 SVA, a measurement of cervical sagittal plane translation, is measured as the distance between a plumb line drawn from the odontoid of C2 and the posteriormost, superiormost point of the C7 vertebral body. Previous studies have shown that a C2 SVA greater than 40 mm is correlated with worse disability; therefore, current recommendations suggest that ACD correction should aim to achieve a postoperative C2 SVA of less than 40 mm. CBVA, on the other hand, allows for the quantification of horizontal gaze and is measured by subtending an angle between a vertical line and a line drawn from the patient’s chin to brow on clinical photographs. Studies have demonstrated that the CBVA should be corrected to 10 degrees if possible, and CBVA correction has been shown to result in improvements in horizontal gaze, gait, and ADLs.

Unlike the C2 SVA and CBVA, there is not a well-established cervical lordosis (CL) threshold that has been shown to improve HRQOL outcomes in patients with ACD. , Although increased kyphosis has been associated with increased pain , a multitude of studies have failed to demonstrate a consistent relationship between CL and postoperative outcomes. , , There are a number of potential reasons for the lack of association seen between CL and patient HRQOL outcomes. CL can vary significantly from person to person, with normal CL values ranging from ‒25 to 44 degrees. , Further compounding the difficulty of establishing a postoperative CL goal is that the cervical spine can experience changes in alignment to compensate for sagittal deformities present in other regions of the spine ; in these patients, the abnormal cervical curve is compensatory to deformity in the other regions. , Consideration of other alignment parameters, such as the T1 slope, can help in determining if an abnormal cervical curve is compensating for a deformity elsewhere in the spine.

The T1 slope is an important measure for assessing overall cervical sagittal balance and identifying the deformity driver region. The T1 slope is defined as the angle between a line that is parallel to the T1 end plate and a horizontal line. A T1 slope of greater than 30 degrees is typically indicative of a sagittal deformity involving the upper thoracic spine or even more distal spine; this results in translation of the cervical spine and head in the patient. , The T1 slope can be used with the C2 slope, a measurement of the angle between the end plate of C2 and the horizontal plane, to assess the relationship between cervical and thoracolumbar alignment. If the C2 slope is low and the T1 slope is high, this suggests the driver of deformity is distal to the cervical spine. If the C2 slope is high and the T1 slope is low, then this indicates a primarily cervical spine–driven deformity. A difference of greater than 17 degrees between the T1 slope and CL also suggests a cervical deformity, even with a concurrent thoracolumbar deformity present. A combined deformity can often present with the C2 slope and T1 slope both being high.

Surgical Strategies for the Correction of Cervical and Cervicothoracic Deformities

Surgical correction of ACD is a complicated and involved process that depends on a multitude of factors. There is often a lack of consensus between spine surgeons on the size of construct, approach, and osteotomy grade for a given case. A study conducted by Smith et al. demonstrated a significant disparity in surgical plans for treating ACD patients with mild to moderate deformity; only 50% of surgeons in the study selected the same approach, and there was a wide range in number of vertebral levels suggested for fusion. However, despite the variability in preferred surgical approach, there is a general consensus that the most important considerations for surgical intervention are determining the etiology, rigidity, and type of a patient’s cervical deformity. To aid in complex surgical planning for ACD correction, Ames et al. developed a classification nomenclature for cervical osteotomies ( Table 145.1 ). This classification system allows surgeons to explore osteotomy options for a given deformity type, as well as the degree of correction required given a patient’s unique pathology ( Fig. 145.1 ). Multiple studies have reported the extent of correction that can be achieved based on the approach and osteotomy type used by a surgeon: 11 to 32 degrees of correction can be achieved with an anterior approach, 23 to 54 degrees with a posterior approach, and 24 to 61 degrees using a combined anterior-posterior approach. , The wide range in degrees of correction can be attributed to variance in patient presentation, as well as surgeon experience.

Table 145.1
Ames Cervical Osteotomy Grade
Spine Type Cervical Osteotomy Grade Technique
Flexible 1 Partial joint resection including partial resection of the uncinate joints and/or partial removal of the posterior facets
Flexible 2 Removal of both the inferior and superior articular facets
Rigid 3 Corpectomy
Rigid 4 Corpectomy with associated complete resection of the uncinate joints laterally to the transverse foramen
Rigid/Ankylosed 5 Complete resection of the posterior elements (lamina, spinous process, and facets), closure of the posterior defect, and controlled fracture of the ankylosed anterior column
Rigid/Ankylosed 6 Pedicle subtraction osteotomy (complete removal of the lamina, spinous process, facets, and pedicles at the desired level), followed by creation of a closing wedge osteotomy in the vertebral body
Rigid/Ankylosed 7 Complete vertebrectomy (removal of the vertebral body and uncinate joints anteriorly, and complete removal of the facets, lamina, and spinous process posteriorly)

Fig. 145.1, Illustrations of the Ames Cervical Osteotomy Grades.

Posterior-Based Osteotomies

Posterior-based osteotomies are one of the surgical techniques that can be used to achieve desired correction for ACD. These osteotomies vary in the amount of bone resected and the instability produced. Based on the Ames Cervical Osteotomy Grade, posterior-based osteotomies are included in grades 1, 2, 5, 6, and 7, with increasing grades producing greater amounts of spinal release and allowing for great correction potential.

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