MANAGEMENT OF NEUROMUSCULAR SCOLIOSIS

Neuromuscular scoliosis pertains to coronal plane deformity of the spine in patients with abnormalities of the myoneural pathways of the body. The disorders which cause this type of deformity comprise a group of diseases characterized by a breakdown in the normal neural integrated pathway that includes the brain, spinal cord, peripheral nerves, neuromuscular junction, and muscles. Characteristically, patients with these diseases have poor head control, lack of neck and trunk balance, and discoordination.⁸² These diverse diseases and conditions share many common features, and patterns of natural history, evaluation, and management.⁴⁷ The final functional path in this abnormal sequence is the muscle unit, which manifests dysfunction through decreased motion (flaccidity), increased motion (spasticity), or out-of-sequence motion (dyskinetic).⁸² Scoliosis associated with these neuromuscular dysfunctional states is classified by the Scoliosis Research Society into the following system:⁹

• Neuropathic

  • Upper motor neuron

    • Cerebral palsy

    • Spinocerebellar degeneration

      • Friedreich's ataxia

      • Charcot-Marie-Tooth disease

      • Roussy-Lévy disease

    • Syringomyelia

    • Spinal cord tumor

    • Spinal cord trauma

  • Lower motor neuron

    • Poliomyelitis

    • Other viral myelitides

    • Traumatic

    • Spinal muscular atrophy

      • Werdnig-Hoffmann disease

      • Kugelberg-Welander disease

    • Dysautonomia (Riley-Day syndrome)

• Myopathic

  • Arthrogryposis

  • Muscular dystrophy

    • Duchenne's muscular dystrophy

    • Limb-girdle dystrophy

    • Fascioscapulohumeral dystrophy

  • Fiber-type disproportion

  • Congenital hypotonia

  • Myotonia dystrophica

With so many causes for neuromuscular scoliosis, the patterns and incidence vary with each patient and each disease. In contrast to the treatment of curve patterns found in idiopathic scoliosis, with which most spinal surgeons are most familiar, the patterns in neuromuscular conditions are quite varied. Idiopathic scoliosis curve patterns are well recognized and constant with a consistent lordoscoliosis found in thoracic curves. Although some neuromuscular conditions produce patterns similar to idiopathic scoliosis, others present as long C-shaped curves collapsing into scoliosis or kyphosis, often extending into and including the sacrum as part of the curve.⁴⁷

Kyphosis is an important part of the neuromuscular deformity pattern and must be carefully considered in the evaluation of these deformities. The kyphosis is characteristically due to compromise in the muscular function of dynamic support for vertebral column stability.⁸² This compromise in support is associated with a postural curve that compromises head and neck positioning, which worsens in the growing spine. Small curves can produce asymetric forces on the vertebral end plates paving the way for the relentless development of a progressive deformity with permanent disk, vertebral, and facet joint alterations¹⁴ via the Heuter Volkmann law. The end plate on the concave side of the curve, whether it be in the sagittal or coronal plane, is subject to increased compression causing decreased growth. On the convex side, growth is subject to decreased loading causing an increased growth. This increased growth can result in a wedge-shaped deformity occurring in the vertebral body, which can worsen over time.⁹⁴ Because of this and other factors, the earlier a curve's onset, the greater is the potential for increased severity and progression of the deformity over time. Weakness in the bone structure itself brought on by disuse, osteopenia, and anti-seizure medication induced osteomalacia adds to the weakness of the bone structure in the individual vertebral deformity. Spinal deformity in neuromuscular scoliosis results from a complex set of interactions between adverse biomechanical conditions superimposed on compromised biologic factors in the patient.