Posterior-Anterior-Posterior Treatment of Severe Cervical Kyphotic Deformity

Christopher T. Martin

John M. Rhee

Radiologic Assessment—Key Factors to Consider on X-ray, MRI, CT

Upright lateral, anteroposterior, and flexion-extension views should be obtained.
A 36-in full-length radiograph is helpful to assess global alignment in the setting of cervical kyphosis (Figure 10-1).
- The full-length x-ray can help in deciding the distal fixation point depending on global alignment in the thoracic spine.
Assessment of the deformity’s flexibility is crucial for preoperative planning.
- CT cuts should be closely reviewed for evidence of ankylosis, which may limit the passive correction of the deformity (Figure 10-2).
- Supine sagittal images can provide an additional estimation of how much passive correction can be obtained with positioning on the table (Figure 10-3).
Back-front-back cervical approaches are usually reserved for patients with ankylosed or rigid/nonflexible deformities. Patients with flexible deformities can usually be approached with an anterior only, posterior only, or a front-back approach, depending on the magnitude of deformity.
The C2-C7 sagittal vertical alignment is a plumb line measured from the center of C2 to the posterior C7 vertebral body (Figure 10-4).
The T1 slope is roughly analogous to pelvic incidence in the lumbar spine and is an indicator of the amount of subaxial lordosis necessary to maintain an upright posture (Figure 10-4).
The chin-brow vertical angle approximates horizontal gaze and is measured as the angle between a line drawn from the patients’ chin to brow and a vertical reference line (Figure 10-5).

Figure 10-1 ▪ Full-length standing scoliosis radiographs of a patient with a severe fixed sagittal imbalance in the cervical spine. She had several previous operations done elsewhere, both anteriorly and posteriorly, with removal of implants for infection. She subsequently developed progressive kyphosis in the cervical spine with myelopathy.

Figure 10-2 ▪ Left parasagittal, midline, and right parasagittal CT cuts from the patient in Figure 10-1 show that the patient is ankylosed overall from C2 to C7 through various regions (ie, right vs left facets, disk spaces) as a result of prior surgery. There is a nonunion through the C5-6 disk space, although the posterior facets are fused at C5-6.

Figure 10-3 ▪ Sagittal T2 MRI demonstrates mild ventral cord flattening secondary to kyphosis. These supine images show that in comparison to the standing films, there is some correction of the deformity through the nonankylosed levels above and below the fused areas.

Figure 10-4 ▪ Sagittal alignment of the cervical spine (different patient than in Figure 10-1). The center of gravity of the head is approximated by a plumb line dropped from the external auditory meatus (white line). The C2-7 sagittal vertical alignment is the perpendicular (white arrow) from the posterior superior corner of the C7 endplate to a plumb dropped from the center of C2 (red line). T1 slope is the angle between the superior endplate of T1 and the horizontal (angle subtended by yellow lines).

Figure 10-5 ▪ The chin-brow vertical angle (CBVA) approximates the patient’s horizontal gaze (different patient than in Figure 10-1). Patients with a higher CBVA require increased lordosis correction in order to allow for appropriate forward vision when standing and walking. This patient with axial neck pain underwent a multilevel cervical laminectomy and suboccipital craniectomy at an outside institution. Despite areas of regional kyphosis, there remains overall upright gaze and a low CBVA.

Anesthesia/Neuromonitoring Concerns

We recommend video-assisted intubation to avoid excessive cervical extension during intubation of myelopathic patients. In some cases, awake fiberoptic intubation may be necessary if the anesthesiologist is unable to pass the endotracheal tube with video assistance only.
We use both motor evoked potentials and somatosensory evoked potentials in patients undergoing a deformity correction.
Baseline motor and sensory potentials may be obtained prior to positioning.
The patient’s mean arterial pressure (MAP) should be maintained normotensive to slightly hypertensive throughout the case in order to minimize the risk of cord hypoperfusion. In general, we aim to maintain the patient’s preoperative baseline MAP, or a minimum of 80 mm Hg.

First Posterior Stage

The initial positioning is prone. Patients with severe cord compression may develop neurologic symptoms when extension exceeds a certain position. Thus, it is useful to examine the patient preoperatively to determine the maximum comfort level of neck extension.
Mayfield tongs are applied.
The patient is carefully rolled prone and the head is locked to the bedframe. If extension is unlikely to cause cord compression, hyperextending the neck can give some indication as to flexibility of the deformity under anesthesia. However, because the final neck position is not determined during this stage, it is not critical that the neck be hyperextended at this point in those for whom extension will exacerbate neurologic compression prior to decompression or deformity correction.

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