1 General Considerations

As opposed to idiopathic scoliosis, patients with neuromuscular scoliosis are physically impaired and functionally disabled. This includes a restriction or lack of ability to perform normal activities. Any therapeutic strategy should aim at prevention of future decline (symptoms, function, death), improvement of the current state (symptoms, pain, respiratory, and physical disability) under consideration of external factors in the disablement process such as behavioural, lifestyle, psychological, medication, external supports, rehabilitation, and social and physical environment.

Impaired motor control of spinal muscles due to neuromuscular diseases with spasticity or hypotonia may lead to scoliosis in up to 90% of patients. The probability of its development inversely correlates with ambulatory abilities; very high rates of scoliosis in non-ambulators with poor head control (Madigan and Wallace 1981). Associated negative predictors are osteopenia and concomitant congenital malformations which cause rapid progression (collapsing spine). The onset of spinal deformities depends on the evolution, the extent, and the severity of the functional component and the involvement of trunk muscles. The natural history of the specific underlying neuromuscular pathology dictates the risk of progression and determines therapeutic strategy, particularly the ideal time point for a surgical intervention. In contrast to idiopathic spine deformities which usually evolve in otherwise healthy individuals, neuromuscular patients bear other medical issues (crooked spine in a sick patient) that largely influence the risk profile.

Growth is just one of these many issues. Accordingly, deformities already developed in childhood to a level where treatment – usually a “buy time” strategy until definitive fusion – is warranted. The pubertal growth spurt stiffens the initially flexible curve which shows a more postural character at the beginning.

This pathologic multisystem complex persists through adolescence into adulthood as a lifelong challenge. It involves a variable compound of poor nutrition, soft-tissue conditions, soft bone, pulmonary infections, urogenital infection, cardiac problems, previous spine surgery, caregivers, orthotic management, social workers, family, and the patient with his or her highly individual needs. Mental retardation may or may not be part of a neuromuscular condition. In non-CP patients it is often not or only to a lesser degree an issue.

Spine-wise, coronal decompensation is the biggest issue. Hyperkyphosis further decreases the patient’s interaction and verbal communication. The basic therapeutic goals are above all a re-balancing of the spine to provide trunk stability, maintain sitting, standing, or walking ability. Hence, a solid base is built for the individual, allowing optimal motor and cognitive development. Seating adjustments and wheelchair modifications have a supportive role but do not provide an isolated long-term solution. Bracing advocated as the primary therapeutic mainstay has generally no impact on the progression rate. It is often challenging or impossible from the start in those mostly underweight patients and bears the risk of pressure sores and skin ulcerations. In addition, it may negatively interfere with respiratory function or gastrointestinal issues like feeding tubes. Serial casting is an alternative but requires repetitive anesthesia, is in most places a lost art, and bears the same shortcomings as the brace. As a consequence, curve progression inflicts on the spine surgeon the decision between an operative growth-sparing buy-time procedure until spinal fusion or a primary definitive instrumented fusion. Therapeutic strategy and timing of surgery heavily depend on the natural history of the disease process. In strong contradiction to idiopathic scoliosis coronal Cobb angle and residual growth are not the most prominent parameters of the decision-making process. Particularly the cumulating risks for repeat anesthesia and surgery of growth-sparing techniques should be weighed out against the shortcoming of early spinal fusion (Hasler et al. 2010). Weight-bearing growing implants for the lifetime of their use are susceptible to loosening, failure, skin sloughs, and wound infections and the disadvantages of repeat hospitalization (germs, psychological trauma, indirect costs to family and caregivers, allergies to adhesives, missing school, etc.). A strategy with repetitive surgery comprises an average of four to five interventions, two complications, one unplanned surgery per patient and a 25% chance of wound complications. The risks and complications are directly related to the severity of the neurological impairment. Infection is the main risk and correlates to poor nutrition, delicate soft-tissues, and wound tension.

Somatosensory-evoked potential (SSEP) and motor-evoked potential (MEP) monitoring during spinal intervention for children with substantial (standing transfer) motor function preoperatively are mandatory. It is highly recommended to include the upper extremities as shoulder–arm and hand function is crucial for independence of wheelchair-bound individuals. This applies to all types of intervention since arm positioning may harm the plexus but is specifically recommended for placement of VEPTR rib cradles. Fixation to the first rib and excessive lengthening has to be avoided to prevent cranial migration of the upper fixation.

In conclusion, operative interventions should be restricted to specialized centers where an interdisciplinary approach is routine and high-standard perioperative management including respiratory care, prevention of pressure sores, and orthosis-free quick mobilization is provided.

Numerous issues specific to certain diseases are highlighted in the following sections.