What Is Neuromuscular Scoliosis (NMS)?

Neuromuscular scoliosis is a spinal deformity associated with neuromuscular disorders such as cerebral palsy, muscular dystrophies, or paralysis. The spine deformity is caused by an imbalance of truncal muscles. It often presents at an early age and can become severe as the patient grows, often involving the entire thoracolumbar spine.

How Does NMS Differ from Idiopathic Scoliosis (IS)?

Idiopathic scoliosis has no definite known cause and is classified by age group:

• 
  

  Infantile scoliosis <3 years

  
  
• 
  

  Juvenile scoliosis 3–10 years

  
  
• 
  

  Adolescent scoliosis >10 years – most common

Unlike NMS, idiopathic scoliosis does not continue to progress with skeletal maturity and is typically associated with mild comorbidities if at all.

What Types of Comorbidities Might a Patient with Any Scoliosis Have?

For patients with IS, the main complication is disfigurement of the torso. Some patients may also present with mild pain, although severe pain is uncommon and warrants further evaluation.

Of greater concern is the cardiopulmonary complications that can arise from scoliosis. While NMS patients are more likely to present with severe curvatures, patients with IS greater than 50 degrees may also develop cardiopulmonary difficulties. Restrictive lung disease occurs due to a decrease in vital capacity. Pulmonary hypertension due to severe restrictive lung disease and chronic hypoxia may develop in patients with extreme curvature.

Patients with NMS often have other conditions such as sleep apnea, impaired swallow and gag reflexes, impaired respiratory musculature, gastroesophageal reflux, and limited mobility. All these co-morbidities may increase the risk of aspiration or infectious pneumonia.

What Is the Cobb Angle?

The Cobb angle is a measure of the curvature of the spine (Table 47.1). It is the angle formed by the perpendicular lines between the upper surface of the top vertebra and the lower surface of the bottom vertebra (Figure 47.1). An angle of greater than 10 degrees is considered abnormal and surgical intervention usually is only warranted for angles greater than 40 degrees. The correlation between the Cobb angle and patient condition is shown in Table 47.1.

Figure 47.1 (A) Preoperative X-ray demonstrating the calculation of the Cobb angle. (B) Intraoperative image showing placement of pedicle screws (white arrows) and correction rods (black arrow) prior to curvature correction.

Review the Main Surgical Stages of Scoliosis Correction Surgery and Related Anesthetic Implications

After induction of anesthesia, neuromonitoring electrodes are placed and baseline levels are obtained: the anesthetic should be stable at this point, i.e., Total intravenous anaesthesia (TIVA) started and not rapidly changing. A bite block must always be in place prior to neuromonitoring to protect the tongue and should be secured to avoid dislodgement. The tongue should be in the middle of the mouth free of any pressure from other lines (e.g., oral glucose tolerance (OGT)/temperature probe). Motor testing should be performed under vision to assure the tongue is not trapped by the teeth.

The patient is positioned prone and padded. All pressure points should be checked and padded appropriately. Auscultation for bilateral breath sounds should occur prior to incision. Antibiotics should be administered; however, care must be taken to avoid greater than one hour from administration to incision as the preparation is often lengthy.

Surgical exposure is associated with significant blood loss and stimulation. Surgeons will often request controlled hypotension and occasionally a single dose of neuromuscular blockage to prevent large muscle twitch with electrocautery. A short- acting neuromuscular blocker should be used and communicated with the neuromonitoring technician.

The spinous processes are removed and the pedicles exposed, also associated with progressive blood loss.

Pedicle screws are inserted bilaterally at each level to be corrected. Evoked potentials should be checked with each screw placement to ensure stability.

Vertical rods are then inserted, secured, and the curvature correction performed. Neuromonitoring should be carefully assessed for loss or reduction of signals.

Autologous and reconstituted bone matrix are packed into areas between surgical hardware and native bone to promote strong bond formation. TIVA should be adjusted planning for emergence.

Surgical closure: takes 30–60 minutes; termination of TIVA should be considered to avoid emergence delays. Long-acting liposomal bupivacaine (Exparel) may be used at the incision site to reduce postoperative pain.