Neuromuscular spinal deformities

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Why do patients with neuromuscular disorders develop spinal deformities?

Neuromuscular spinal deformities develop in patients with underlying neuropathic or myopathic disorders due to trunk muscle weakness, spasticity, or spinal imbalance, which compromise the ability to maintain normal alignment of the spine and pelvis. Asymmetric spinal column loading of the immature spine leads to asymmetric vertebral body growth due to the Hueter-Volkmann principle, which states that increased loading across an epiphyseal growth plate inhibits growth while decreased loading accelerates growth. The severity of a deformity is influenced by a range of patient-specific factors, including the underlying diagnosis, the type and extent of neuromuscular involvement, ambulatory status, and skeletal maturity. A broad spectrum of spinal deformities may develop, including scoliosis, hyperkyphosis, hyperlordosis, and complex multiplanar deformities.

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How are neuromuscular spinal deformities classified?

Neuromuscular spinal deformities referred for evaluation and treatment include cerebral palsy, Duchenne muscular dystrophy, spinal muscular atrophy, myelodysplasia, posttraumatic deformities, and Rett syndrome. Neuromuscular disorders may be classified as neuropathic (affecting either the upper or lower motor neurons) or myopathic . Certain conditions such as myelodysplasia and posttraumatic deformities may present with both upper and lower motor neuron involvement.

• MYOPATHIC DISORDERS

  • 1.

    Muscular dystrophy

    • Duchenne type

    • Limb-girdle

    • Facioscapulohumeral

  • 2.

    Arthrogryposis multiplex congenita

  • 3.

    Congenital hypotonia

  • 4.

    Myotonia dystrophica

• NEUROPATHIC DISORDERS

  • A.

    Upper motor neuron lesions

    • 1.

      Cerebral palsy

    • 2.

      Spinocerebellar degeneration

      • Friedreich ataxia

      • Charcot-Marie-Tooth disease

      • Roussy-Lévy disease

    • 3.

      Syringomyelia

    • 4.

      Quadriplegia secondary to spinal cord trauma or tumor

    • 5.

      Rett syndrome

  • B.

    Lower motor neuron lesions

    • 1.

      Spinal muscular atrophy

    • 2.

      Poliomyelitis

    • 3.

      Dysautonomia (Riley-Day syndrome)

    • 4.

      Traumatic

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How common are neuromuscular spinal deformities?

The incidence of spinal deformities varies across different neuromuscular disorders and is dependent on patient-specific factors such as the extent neuromuscular involvement and the criteria used to define a spinal deformity. Some general incidence ranges for neuromuscular scoliosis include: cerebral palsy (25%–100%), myelodysplasia (60%–100%), spinal muscular atrophy (67%), Friedreich ataxia (80%), Duchenne muscular dystrophy (90%), and spinal cord injury before 10 years of age (100%).

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List important differences between neuromuscular scoliosis and idiopathic scoliosis.

• Evaluation of neuromuscular scoliosis requires assessment of the underlying neuromuscular disease in combination with the spinal deformity. In contrast, idiopathic scoliosis is a spinal deformity occurring in an otherwise normal patient.

• Multidisciplinary evaluation is required for problems associated with the underlying neuromuscular disease in patients with neuromuscular scoliosis (e.g., contractures, hip dislocations, seizures, malnutrition, cardiac and pulmonary disease, urinary tract dysfunction, developmental delay, pressure sores, insensate skin).

• Neuromuscular scoliosis usually develops at an earlier age than most cases of idiopathic scoliosis, often before age 10, and is more likely to progress.

• Neuromuscular curves tend to be longer, more rigid, and involve more vertebrae than idiopathic curves.

• Neuromuscular scoliosis often presents in combination with sagittal plane deformities.

• Neuromuscular curves are frequently accompanied by pelvic obliquity, which may compromise sitting ability and upper extremity function.

• Brace or cast treatment does not provide a long-term solution for most neuromuscular curves, although such treatments are helpful to improve sitting posture and provide temporary curve control in specific circumstances.

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What are some key steps in the initial evaluation of neuromuscular spinal deformities?

A general clinical examination is the first step in evaluation and includes a detailed birth, developmental, and family history. Physical examination includes detailed assessment of the spine, extremities, and thorax, including neurologic function, pelvic obliquity, trunk balance, chest wall excursion, and inspection for cutaneous markers of systemic disorders. Initial imaging evaluation consists of biplanar radiographs or slot-scanning radiography, which includes the entire spine and pelvis. Upright radiographs are obtained in patients who are able to stand. Patients who are able to sit without hand support are assessed in the sitting position. Patients who are unable to sit are evaluated with recumbent anteroposterior and lateral radiographs. The examiner should assess curve magnitude, curve progression, spinal balance, pelvic obliquity (if present), and curve flexibility. Spinal magnetic resonance imaging (MRI) is required if intraspinal problems (e.g., syrinx, tethered cord) are suspected. Additional testing may include blood tests, computed tomography, ultrasound, bone density scans, muscle biopsy, pulmonary function tests, and electromyogram. Patients and families diagnosed with neuromuscular spinal deformities benefit from coordination of care by a multidisciplinary team and in some cases referral for genetic and family counseling.

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What radiographic features are characteristic of typical neuromuscular curves?

Neuromuscular curves are often S-shaped curves or long, sweeping C-shaped curves with a curve apex in the thoracolumbar or lumbar region that extends to the pelvic region. Significant sagittal plane deformity often accompanies coronal plane deformity. Pelvic obliquity is common and poses a major problem because it creates an uneven sitting base.

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What are options for nonoperative treatment of neuromuscular spinal deformities?

Nonoperative treatment options include observation, serial casts, orthoses, wheelchair and seating modifications, and specific medical treatments directed toward the underlying neuromuscular disorder. Observation is considered for patients with small nonprogressive curves, patients with severe developmental disability and large curves without associated functional loss, and patients with contraindications for major spinal reconstructive surgery. Although brace treatment does not positively affect the natural history of neuromuscular curves, in select patients it is used to improve sitting posture and control spinal curves temporarily to allow additional spinal growth prior to definitive surgery. Wheelchair and seating modifications can also be used to improve seating for patients with severe deformities. Orthotic management is challenging due to poor muscle control, impaired sensation, pulmonary compromise, impaired gastrointestinal function, obesity, and cognitive impairment.

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What are the indications and treatment options for neuromuscular spinal deformities?

The decision to intervene surgically for treatment of a neuromuscular spinal deformity depends on a range of factors, including etiology of the underlying neuromuscular disorder, deformity magnitude, skeletal maturity, and associated medical comorbidities. The operative treatment options for neuromuscular spinal deformities include both nonfusion and fusion surgical techniques.

Nonfusion or “growth-friendly” surgical techniques are considered for patients with early-onset neuromuscular scoliosis (<10 years of age) to treat curves that are not adequately controlled with bracing. Various strategies are used to control such curves and can prevent or limit progression without adversely affecting future lung growth and function. These include use of various devices implanted through a posterior surgical approach such as expandable rod systems, which require periodic open surgical lengthening; magnetically controlled expandable rod systems, which allow for noninvasive lengthening; growth-guidance systems; and the vertical expandable prosthetic titanium rib (VEPTR).

Surgical techniques intended to achieve fusion are considered for patients who are not candidates for growth-friendly surgery to treat progressive deformity, unacceptable trunk shift, or pelvic obliquity that affects standing or sitting balance or positioning. Operative treatment has been suggested when progressive curves exceed 50° or when patients develop trunk decompensation. Earlier surgical treatment is advised for patients with Duchenne muscular dystrophy (when curves reach 20°) due to predictable pulmonary deterioration associated with further curve progression. Neuromuscular curves up to approximately 90° are most commonly treated with posterior spinal instrumentation and fusion, while larger or rigid curves require more complex anterior and posterior procedures that are associated with higher morbidity. The most common procedure for neuromuscular scoliosis is a long posterior fusion with posterior instrumentation extending from T2 to the pelvis, although fixation ending at L5 distally is considered in ambulatory patients with a level pelvis whose deformity ends proximal to L5.

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List some important preoperative considerations in evaluation of patients with neuromuscular spinal deformity.

Assessment by a multidisciplinary team is critical and includes assessment of:

• Functional status: Assess ambulatory ability, sitting ability, hand function, cognitive ability.

• Pulmonary function: Inquire regarding a history of upper respiratory infection or pneumonia; assess for chronic aspiration; perform pulmonary function testing if possible.

• Gastrointestinal function: Assess for gastroesophageal reflux and intraabdominal volume compromise.

• Cardiac assessment: Evaluation is critical in disorders such as Duchenne muscular dystrophy or Friedreich ataxia due to associated cardiac anomalies.

• Nutritional status: Address deficits to help prevent impaired wound healing and decrease infection risk.

• Hematologic assessment: Evaluation and correction for preoperative coagulopathies and planning to optimize anticipated blood loss is an important part of preoperative assessment.

• Seizure disorders: Require assessment by a neurologist and includes confirmation of appropriate levels of antiseizure medications.

• Metabolic bone disease: Osteopenia is common secondary to disuse, poor nutrition, and anticonvulsants, and benefits from preoperative optimization.

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