Neuromuscular Disorders in the Pediatric Spine

Natural History of Neuromuscular Scoliosis

Patients with scoliosis secondary to neuromuscular disorders can present as complex cases for surgeons due to the combination of large curve magnitudes, earlier age of onset, decreased tone and strength of the surrounding musculature due to the progression of the underlying neuromuscular disease, increased pelvic obliquity, lack of mobility, and significant comorbidities that present in this patient population. These comorbidities extend outside just the musculoskeletal complications, increasing the complexity of surgery in these patients and highlighting the differences between them and patients with adolescent idiopathic scoliosis (AIS). Whereas the greatest risk factor for curve progression in both populations is linked to spinal growth (often around puberty), and thus tends to taper with skeletal maturity, those with underlying neuromuscular disorders can also progress past this point because of the loss of stabilizing musculature allowing proper spinal alignment, especially in those who are wheelchair-dependent. Thus, left untreated, these curves can progress to the point of impairing respiratory function or causing gastrointestinal issues. A study in patients with Duchenne muscular dystrophy looking at the correlation between pulmonary function and scoliosis found that each 10-degree increase in thoracic scoliosis was associated with a decrease in forced vital capacity (FVC) of 4%. The use of steroids in patients with Duchenne muscular dystrophy has dramatically improved their respiratory function and delayed their loss of motor function, but historically it was beneficial to consider surgery early in these patients before their pulmonary function had deteriorated. Generally, in other types of neuromuscular scoliosis, surgery is considered with progressive curves exceeding 50 degrees.

Several studies have shown that neuromuscular curves presenting even in skeletally mature patients have a tendency to progress over time. The combination of impaired muscle strength and abnormal tone may predispose these patients to greater risk of curve progression, and curve progression often continues to occur in adulthood. Generally, larger curves with skeletal growth remaining have been reported as risk factors, but variability exists, so these patients should be followed through their adulthood with serial imaging.

General Goals of Treatment in the Neuromuscular Population

As with all surgeries, a discussion regarding goal of care should be initiated with families before treatment. Traditional goals in the idiopathic scoliotic population differ from those in the neuromuscular population, and family expectations should be addressed. The focus of treatment shifts more from cosmesis to increased quality of life measures. A balance must be struck between the potential benefits of treatment and the potential risk of complications. Samdani and colleagues found that the perioperative complication rate following spinal surgery in patients with CP is as high as almost 40%. Thus setting realistic expectations for patients and their families is important to achieving a successful result.

Bracing is seen as an effective and even sometimes curative option in those with idiopathic scoliosis; however, this is not the case in those with underlying neuromuscular disease. In neuromuscular scoliosis, bracing is used as a bridging or temporizing option and functions to delay, not cease, curve progression until a later age when definitive surgical correction is more favorable. Miller and colleagues published a study on bracing in patients with CP scoliosis and found that there was no significant difference in the curves in those who were braced versus those who were not.

General Preoperative Considerations

As stated before, because of the large risk and the high prevalence of comorbidities in this population, proper and thorough preoperative planning is necessary to optimize patients for surgery and avoid postoperative complications. A thorough history and physical, identifying any comorbidities, may change the operative plan or even the decision to operate at all. Special attention should be paid to the degree of independence (and therefore level of care needed), posture, degree of dependence on assistance devices, presence of pressure sores, and onset of pain. Patients who are dependent on others for their activities of daily living require different considerations than those who do not. Following a full medical history, physical examination should start with height and weight. If the patient is cachectic or obese, proper nutritional optimization may be necessary before surgery. Measurements should be taken to determine head tilt, shoulder elevation, pelvic obliquity, and trunk balance, noting any rib cage deformities and the degree of hip mobility. Flexibility of the spine should be determined in both the coronal (using a side bending test) and sagittal planes (by laying the patient supine and attempting to reduce the thoracic kyphosis). Noting the patient’s ability to balance his or her head over the pelvis during sitting or ambulating is also important. The patient’s degree of ability to ambulate is also important in the determination of the caudal lower instrumented level. Finally, a full neurological examination is necessary to determine any possible deficits that may change the operative plan. Loss of abdominal reflexes, for example, noted by stroking the abdomen and observing for an underlying muscle contraction, could possibly mean the presence of syringomyelia and should be investigated with magnetic resonance imaging (MRI) of the spine.

Full radiographic evaluation preoperatively allows for careful surgical planning to determine the extent of the surgery and the size of the construct that will be needed. This should start with an upright sitting or standing (when possible) posteroanterior and lateral view of the thoracolumbar spine. Bending radiographs will help to determine the flexibility of the curve. Traction films or supine films may also provide insight into the curve flexibility. The pelvic obliquity should be measured between a line over the iliac crests subtended to the horizontal. Preoperative computed tomography (CT) scans can also be useful at the discretion of the surgeon for surgical planning to determine any variability in the normal anatomy that was not noted by plain radiographs, as well as the shape and bone quality of the sites of insertion for pedicle screws. Finally, MRI can be used to determine if there are any neurological concerns, such as a tethered cord or syrinx; however, they are typically only performed on select patients, such as those with spinal dysraphisms.

As discussed earlier, preoperative planning in this population should have a true multidisciplinary approach due to the high-risk nature of this population. Pruijs and colleagues provided a detailed example of their hospital treatment team’s approach pre- and postoperatively in patients with neuromuscular scoliosis. The team mainly consists of a pediatric orthopedic surgeon, a physician specializing in rehabilitation medicine, a pediatric neurologist, and a pulmonologist specializing in ventilation. Based on patient need, dieticians, gastroenterologists, urologists, cardiologists, hematologists, psychologists, and others may also be added to minimize the risk of postoperative complications.

In all surgeries, but especially in this population, prevention of surgical site infection is paramount. One of the ways physicians can lower the rate of infection in those with neuromuscular scoliosis is through proper preoperative nutritional optimization. In a group of 44 patients with CP, 24 patients who had a serum albumin of at least 3.5 g/dL and a lymphocyte count of at least 1.5 g/L preoperatively had a lower infection rate than their comparative group with lower values. However, it should be noted that not only malnutrition, but also overnutrition, can lead to postoperative complications. Basques and colleagues also found that infection rates increased in clinically obese patients with a body mass index in the 95th percentile or higher. Therefore careful attention should be paid to involving nutritional support staff, whether it be admitting the patient preoperatively for tube feeds or devising a plan to bring a patient down to a healthier weight and to better nutritional status to achieve the best outcome.

Vitale and colleagues also identified proper preoperative nutritional evaluation to decrease infection rates in their “Best Practice Guideline for surgical site infection prevention in high-risk pediatric spine surgery.” However, they also identified several other factors that were agreed upon by consensus. The group, consisting of 20 pediatric spine surgeons and three infectious disease physicians, detailed 14 points that were agreed upon after careful review of the current literature. These points include practices from providing chlorhexidine scrub to patients for the night before surgery to the use of antibiotics intraoperatively and the use of surgical drains.

Before surgery, these patients should also undergo a full cardiopulmonary evaluation. Various underlying neuromuscular disorders can present with a variety of cardiac and pulmonary abnormalities, and thus must be identified before proceeding to the operating room. Soudon and colleagues created an algorithm for this patient population to thoroughly evaluate these patients before surgery. Thorough laboratory work and cardiac workup (electrocardiogram and echocardiogram) with pulmonary function testing should be performed, with correction of any abnormalities where possible. Optimizing pulmonary function status in these patients can decrease the overall rate of respiratory related complications postoperatively. Pesenti and colleagues found that the use of pre- and postoperative physiotherapy and noninvasive ventilation decreased their pulmonary-related complication rates. Some have found that decreased FVC may also be related to respiratory complications ^, ; however, others have found contradictory results. Thus, although respiratory optimization is generally considered beneficial for patients, further investigation is necessary to determine which measures are critical.