Posterior Correction of Scoliosis

Christopher T. Martin

Dheera Ananthakrishnan

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

Standing 36 in anteroposterior (AP) and lateral scoliosis radiographs are standard in the workup of a patient with spinal deformity. The patient’s hips and knees should be fully extended in order to get an accurate assessment of the patient’s true sagittal balance.
Traction views or side bending films are helpful in assessing the flexibility of the deformity (Figure 16-1, right). Traction views are more helpful with the larger curves (over 60°).

Figure 16-1 ▪ Lateral, posteroanterior, and traction anteroposterior scoliosis radiographs of a 56-year-old woman with severe activity-related back pain.

Sagittal alignment should be assessed including the sagittal vertical alignment, pelvic incidence, lumbar lordosis, and pelvic tilt (Figure 16-2).

Figure 16-2 ▪ Sagittal vertical alignment (SVA, [A]), pelvic incidence (PI, [B], yellow angle), lumbar lordosis (LL, right image, red angle), and pelvic tilt (PT, right image, green angle) are commonly measured to assist in assessing spinal deformity. The SVA is a vertical reference line dropped from the center of the C7 body (yellow line) and measured from the posterior superior aspect of the S1 vertebral body (red line). PI is the angle from a reference line drawn perpendicular to the S1 endplate and the point at the center of the femoral heads. PT is the angle between a vertical reference line dropped to the center of the femoral heads, and the point at the center of the S1 endplate. LL is the Cobb angle measured from the superior endplate of L1 to the superior endplate of S1.

Patients with flexible deformities and mild or no sagittal imbalance may be candidates for posterior correction alone without a three column osteotomy or anterior disk space releases (Figure 16-1). Adolescent idiopathic scoliosis is often treated from posterior approach alone, as most of these patients have a negative sagittal balance. Adults with untreated idiopathic scoliosis are also often treated from a posterior approach alone.

Positioning

The patient is positioned prone on a Jackson table. Care is taken to ensure the neck is in a neutral position.
The pressure points are well padded. If there is pelvic obliquity, then additional bumps can be placed on the down side to try and provide some derotation.

Anesthesia/Neuromonitoring Concerns

Motor-evoked potentials and somatosensory-evoked potentials of the upper and lower extremities are utilized in deformity correction surgery. When doing long deformity cases, we ask our anesthesiologists to use total intravenous anesthesia because it maintains more stable motor potentials throughout the case that are less likely to degrade due to anesthetic effects.
The patient’s blood pressure may be kept normotensive to slightly hypotensive during exposure to decrease blood loss. Once the corrective maneuvers begin, we generally maintain mean arterial pressure above 80 mm Hg in order to maximize cord perfusion.
In addition, tranexamic acid has been shown to decrease blood loss with no increase in thrombotic complications. Therefore, we regularly use a bolus followed by a weight-based hourly infusion throughout the case.
A multidisciplinary approach to the patient (including anesthesia, medicine, neuromonitoring) is imperative in the deformity patient.

Localization of Incision

A vertical midline incision is made centered over the spinous processes of the thoracolumbar spine. Generally, no preincision localization is performed because the approach is long enough that this is not necessary. Of note is that it is helpful to follow outline of the patient’s spinous processes to minimize soft-tissue disruption during dissection and retraction. Once down to the facet joints, a spinal needle is placed into a facet joint of the surgeon’s choice and then a lateral lumbar radiograph is obtained to verify the level intraoperatively. Of note is that because of the patient’s deformity, it may be difficult to identify the level in one plane only. We have a low threshold for using an AP radiograph and/or fluoroscopy to localize.

Approach