3.1.1 Pulmonary

In many cases of neuromuscular spinal, the pulmonary system is affected by both the neuromuscular disease and the presence of the spinal deformity. This is true whether the diagnosis is totally involved cerebral palsy with a 100-degree coronal deformity or a Duchenne muscular dystrophy (DMD) patient with a 20-degree deformity and progressive muscle weakness. ⁵ While pulmonary function testing (PFT) is not always possible in this diverse patient population due to cognitive comorbidity, spirometry should be obtained when possible. Other methods to test pulmonary function include diffusion capacity and gas dilution methods. Poor PFTs may preclude surgery in the most extreme cases. Otherwise, knowledge of PFTs preoperatively allows for an informed decision-making process with the patient and caretakers. Those patients with poor PFTs are at a higher risk for perioperative complications such as prolonged intubation, ventilator-acquired pneumonia, and need for tracheostomy. Thus, all involved in the care of the patient should be prepared for these events. ⁵

3.1.2 Cardiovascular

Patients undergoing surgery for neuromuscular spinal are at an estimated threefold higher risk of intraoperative cardiopulmonary arrest, when compared with other causes of pediatric scoliosis. ⁶ While this complication remains rare, knowledge of those at risk will improve response to any event, as well as allow for careful discussion with patients and caretakers. Particular attention must be paid to those diagnosed with muscular dystrophies, including DMD, Becker’s muscular dystrophy, and some cases of congenital muscular dystrophy. These diseases are associated with early-onset cardiomyopathy, and preoperative evaluation must include electrocardiogram (ECG) and echocardiogram. ⁷ Congenital muscular dystrophy is also associated with arrhythmias, and pacemaker pad placement at the time of surgery is advisable. Appropriate pharmacologic management of cardiovascular disease is necessary as well, which includes angiotensin-converting enzyme inhibitors in DMD.

3.1.3 Gastroenterology/Nutrition

Malnutrition is not uncommon among patients with neuromuscular disease. This may put them at increased risk for perioperative complications including infection, wound healing difficulties, and pseudarthrosis. ⁸ It may be helpful to check preoperative serum albumin, prealbumin, and transferrin. These serve as some measure of nutritional status and may alert the surgeon to the severely malnourished patient, though the physical appearance will likely lead to this diagnosis before any laboratory value. For those patients that are malnourished, placement of an enteral feeding tube with several months of augmented caloric intake may help optimize them. ⁹ Some authors have promoted the use of parenteral feeding in the perioperative period, though the benefits of this are unclear and this intervention comes at high costs and some risk to the patient. ¹⁰ Consultation with gastroenterology and a nutrition service may help improve the nutritional status of the patient. Bowel habits must be assessed preoperatively to prepare for postoperative care, as prevention of wound contamination is essential. Immobility may also lead to obesity in this patient population. ¹¹ A high body mass index (BMI) has been associated with larger deformities, which is concerning in an already “at-risk” population. ^{12 ,​ 13} Furthermore, obesity has been associated with an increased risk of perioperative complications in adolescent idiopathic scoliosis and adult spinal deformity surgery. ^{14 ,​ 15} It stands to reason that obesity conveys similar risks in neuromuscular scoliosis, given the already high rate of perioperative complication.

3.1.4 Genitourinary

Genitourinary abnormalities such as uncontrolled voiding and bacterial colonization of the bladder are not uncommon, particularly in patients with myelomeningocele. While not serving as contraindications to spine surgery, bladder habits should be evaluated preoperatively. Again, knowledge of preoperative habits and risk factors will optimize postoperative care through anticipation of complications and appropriate counseling of the patient and caregivers. Patients with myelomeningocele and their caregivers may find catheterization difficult and require Mitrofanoff procedures or other rerouting procedures to allow for safe and clean catheterization. A discussion of the potential needs should occur at a preoperative visit. In some cases, the patient or family may prefer to have the rerouting procedure performed before the spine fusion. Patients with frequent urinary tract infections should consider such a procedure before the spine surgery to reduce the risk of bacteremic seeding of the spine.

3.1.5 Ambulatory Status

The ambulatory status of the patient should be evaluated preoperatively as this will influence the choice of lowest instrumented vertebrae as well as call attention to the position of the pelvis with walking. Fusion to the sacrum and ilium likely alters gait mechanics. This is an important point for those patients using platform crutches to bear the majority of weight through the upper extremities. These patients require trunk flexibility to accommodate the paralytic lower extremities, and fusion to the sacrum and pelvis may affect gait to an unacceptable degree. ¹⁶ For this reason in ambulatory patients we will try to stop at L4 or higher and avoid fixing to the sacrum and ilium. For nonambulatory patients, the degree of pelvic obliquity and sitting imbalance should be assessed, as these two factors will influence the decision to fuse to the sacrum and ilium.

3.2.1 Cerebral Palsy

The development of scoliosis in patients with cerebral palsy varies with the severity of neurologic involvement, though the deformities are often progressive if present before skeletal maturity (Fig. 3‑1 a-d, Fig. 3‑2). Spastic cerebral palsy is often characterized by early onset and progression that persists through skeletal maturity. ¹⁷ Patients with quadriplegic involvement and those who are bedridden have the worst prognosis. ¹⁸ Deformities that measure 40 degrees or more may progress into large curves during adulthood, and one may consider surgery at this point in skeletally mature individuals. ^{19 ,​ 20} Scoliosis in the setting of a baclofen pump may progress at a rate faster than the normal natural history, and intervention may be considered when a curve has progressed to 40 degrees or higher. ²¹ These findings have not been ubiquitous, however, and the dichotomy of findings emphasizes the importance of the informed decision-making process. ^{22 ,​ 23 ,​ 24}

The risk of surgery increases significantly once a curve reaches 90 degrees and therefore intervention is recommended if a curve reaches this point at a young age. Bracing is ineffective; therefore, in order to prevent crankshaft phenomenon and allow adequate development of trunk height, growing constructs may be needed if a curve exceeds 90 degrees before the skeletal age of about 9 to 10 years. Fusion for those patients near 10 years of age with curves of this magnitude (>90 degrees) may be the most appropriate option. ²⁵

Growing rods in patients with cerebral palsy have been shown not only to provide control of the deformity, but also to have a high infection rates, up to 30%. ²⁶ Iliac fixation has shown superiority over sacral screws for distal fixation (67% correction vs. 40% for pelvic obliquity and 47% correction for scoliosis vs. 29%) when pelvic obliquity is present. Dual rods also afford better correction and are recommended. ^{26 ,​ 27} More frequent implant-related complication rates have been reported with growing constructs compared to fusion, and thus it is obviously ideal to delay insertion of growing rods for as long as possible. ²⁸ The vertical expandable prosthetic titanium rib (VEPTR) may be useful in cases of early onset neuromuscular scoliosis. ²⁹ A rib-to-pelvic construct avoids disruption of the spine and may maximize growth potential. Magnetically controlled growing rods require limited spinal fusion and allow for lengthening without a return to the operating room. They have shown promise in cases of early-onset scoliosis, including neuromuscular deformity. ^{30 ,​ 31}

Consideration for surgical approach is of key importance. Posterior approaches offer excellent correction, similar to combined anterior and posterior, with shorter intensive care unit (ICU) stays and less morbidity. ^{32 ,​ 33} However, for severe and rigid curves, or those with significant lordosis, an anterior approach may be beneficial by shortening the spine and decreasing the muscle tension needed. ³⁴ Baclofen pumps are often present, though these do not affect complication rates or outcomes. ³⁵ The importance of preoperative optimization, as discussed earlier, cannot be over emphasized in these complicated patients.

3.2.2 Duchenne’s Muscular Dystrophy

DMD is an X-linked recessive mutation in the gene coding for dystrophin. Historically, the progressive muscle weakness associated with DMD has led to scoliosis notorious for steady progression, necessitating surgical intervention. Scoliosis usually occurs once the child is no longer ambulatory and takes the form of a long C-shaped paralytic curve involving the thoracic and lumbar spine. Surgical indications in DMD have changed dramatically with the regular use of steroids. Glucocorticoids have been shown to prolong walking for 2.5 years, in addition to slowing the decline in lung function. ³⁶ Fifteen-year follow-up of patients with DMD found that scoliosis developed in 20% of patients receiving the glucocorticoid deflazacort, a derivative of prednisone, versus 92% of patients not receiving steroids. Seventy-eight percent of the glucocorticoid group in this study were able to avoid surgery, whereas only 8.3% of patients in the nonsteroid group did not need surgery. Corticosteroid treatment is not without risk, however, and cataract formation was common (70%) in those treated with deflazacort. ³⁷ While further work to determine appropriate dosing regimens needs to be done, it is clear that corticosteroids positively affect spinal deformity progression and reduce the need for spinal fusions.

Historically, treatment of scoliosis was recommended prior to the decline of cardiopulmonary function, once the curve reached 20 degrees. ³⁸ This was due, in part, to the combination of progressive weakness of muscles of respiration with the restrictive disease associated with a collapsing deformity as well as the ineffectiveness of bracing in controlling the deformity. However, with glucocorticoid treatment, fusion can now be avoided or delayed until curves are larger, around 50 degrees, or when sitting balance is becoming affected. ^{39 ,​ 40} Of note, anterior approaches are contraindicated, given the potential to further compromise pulmonary function. If nonoperative management is chosen, then serial PFTs should be obtained and followed for evidence of progressive decline. Spinal fusion may help prevent decline in pulmonary function and consideration to surgery should be made in such a case. ⁴¹ Furthermore, a plateau of the vital capacity at 1,900 mL has been associated with rapid progression of the spinal deformity, particularly in those patients younger than 14 years. ⁴²

There is general consensus that spinal fusion should be performed before forced vital capacity (FVC) is less than 30 to 35% predicted, though FVC lower than this is not a strict contraindication to surgery and successful surgeries have been reported. ^{43 ,​ 44} Marsh et al compared a group of patients with FVC < 30% (average 24%) to patients with FVC > 30% and found that there were similar times for postoperative ventilator support and hospitalization between the groups, when one patient in the less than 30% group requiring tracheostomy was excluded. Overall complication rates were 30% in each group, further suggesting that spinal surgery can be performed on patients with FVC < 30%. ⁴⁴ Additionally, Kennedy et al found that there was high patient satisfaction in patients with FVC < 30% (mean 21.6%), with no major complications and all patients extubated immediately postoperatively. ⁴⁵ However, there is also documentation of prolonged ventilator time and respiratory complications in patients with FVC < 30% and therefore the risks and benefits of surgery must seriously be considered in this patient population. It is important to realize that the decline in FVC will continue postoperatively, as a consequence of the ongoing disease process, and this is important to discuss with the family preoperatively. ^{45 ,​ 46}

Cardiomyopathy is indicative of more advanced disease and needs to be factored into surgical considerations. ECG commonly shows abnormalities and echocardiogram should be performed to evaluate left ventricle function. The most common pathologies encountered include inferobasal wall motion abnormalities, which is then followed by left ventricular dilatation. ⁴⁷ Echocardiogram should be performed preoperatively and a multidisciplinary team assessment performed. ⁴⁸ Left ventricular dysfunction on echocardiogram, unlike ECG changes, is predictive of perioperative mortality. ⁴⁹ A normal preoperative cardiac evaluation does not exclude all risks, however, as a fatal cardiac event has been reported in a child with a normal preoperative evaluation (FVC 87%, echocardiogram normal). ⁵⁰ Important to consider and discuss with the anesthesia team is that patients with DMD can have rhabdomyolysis with anesthesia that can cause hyperkalemia and cardiac arrest, in a reaction similar to malignant hyperthermia. ⁴⁷

3.2.3 Myelomeningocele

In cases of myelomeningocele, curves of less than 20 degrees are unlikely to progress, though clinical motor level, ambulatory status, and last intact laminar arch all affect risk for progression and should be factored into treatment. ^{51 ,​ 52} In a review of 46 patients, Muller et al₅₂ outlined the tendency for progression based on Cobb angles and found that curves less than 20 degrees progressed only 1.2 degrees per year, curves between 20 and 39 degrees progressed 3.8 degrees per year, and curves greater than 40 degrees progressed 12.5 degrees per year. While some surgeons feel that when the curve worsens to 50 degrees and sitting balance becomes affected, surgery is indicated, others feel that surgery should be recommended only if there is clear impairment of skin or sitting balance, as there is a high complication rate in patients with myelomeningocele. ⁵³ Spinal fusion has been shown to have an uncertain impact on health-related quality of life, with some studies showing no relation between coronal deformity and self-perception or physical function. Thus, the decision to intervene surgically in these patients must include very careful consideration of risks and benefits ⁵⁴ (Fig. 3‑3).

In the ambulatory patient, special consideration of levels are indicated, as fusion to the pelvis can potentially interfere with ambulation. ⁵⁵ Fusion short of the pelvis can be performed if the apex of the curve is above T12 and there is minimal lumbar rotation. Surgical procedures may need to be coordinated with neurosurgical procedures to address tethered cord and shunt function.