Neuromuscular Scoliosis

Neuromuscular scoliosis (NMS) is a spinal deformity associated with a heterogeneous group of disorders, including cerebral palsy (CP), Duchenne muscular dystrophy (DMD), spinal muscular atrophy (SMA) and spina bifida. Onset is often early, under 10 years, and most patients are wheelchair-bound (non-ambulatory).

Progression. Unlike idiopathic scoliosis, NMS curves continue to progress after skeletal maturity, because of the loss of trunk control and gravity.

Impact. A severe curve costs the patient three things. Sitting balance goes, so the hands are needed for support; the pelvis tilts, and pressure sores follow; and pulmonary function is restricted, so pneumonia becomes a risk.

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The driver. The primary driver is muscle weakness in DMD and SMA, or spasticity in CP. Adolescent idiopathic scoliosis is driven by rotation; NMS is often a collapsing deformity under gravity.

Pelvic obliquity. The pelvis is the foundation of the spine, and in NMS it behaves like a tilted table. The tilt may be suprapelvic, produced by the spinal curve itself, or infrapelvic, produced by hip contracture. Either way the consequences are the same: the ischium on the low side bears the weight and ulcerates, and the hip on the high side is driven into adduction and towards subluxation or dislocation.

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History. Pain is rare in NMS, so a painful child should make you look for a dislocated hip.

• Function: can they sit, and do they use their hands for support?
• Pain: is the curve painful?
• Pulmonary: pneumonia, ICU admissions, CPAP?
• Seizures: frequency and medications
• Nutrition: feeding tube (PEG), weight loss?

Examination. Watch the patient sit: assess sitting balance and head control, and whether they list to one side. Palpate the iliac crests with the patient sitting to judge pelvic obliquity, and look at the ischia for sores. Decide whether the curve is flexible or rigid. Then the hips: a hip flexion contracture greater than 20 degrees exacerbates lumbar lordosis or kyphosis, and look for windswept hips, one abducted and one adducted. Inspect the skin of the back and buttocks for breakdown.

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Radiographs. The spine films are taken sitting; the parameters that matter on each view are set out below.

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Flexibility. Traction or bending imaging changes the operative plan by defining how much correction is achievable without excessive force.

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Optimisation is a team exercise: ICU, paediatrics, respiratory medicine and a dietician.

Nutrition. The most commonly missed optimisation factor. Malnutrition is rampant in this population and G-tubes are often needed; poor nutrition means infection and wound breakdown. Albumin and pre-albumin (or transferrin) are the markers, with an albumin greater than 3.5 g/dL desired and a total lymphocyte count greater than 1500. Optimise the haematocrit, and check a coagulation profile, because valproate can affect platelets and clotting factors.

Respiratory. Pulmonary function tests and a sleep study. An FVC under 30% predicted means post-operative ventilation must be planned for, and carries a high risk of pneumonia and death; when FVC is low, plan extubation to non-invasive ventilation with mechanical cough assist.

Cardiac. DMD patients have a progressive dilated cardiomyopathy, and it is a fatal risk. A detailed echocardiogram and cardiology review are required, and the ejection fraction determines eligibility for surgery.

Seizures. Ensure valproate levels are therapeutic. Post-operative seizures can break rods.

The rest of the checklist.

• Urine: rule out UTI
• Tone: baclofen pump? spasticity?
• Infection clearance: skin, teeth, ears
• Imaging: traction films, pelvic incidence
• Osteopenia: DEXA? bisphosphonates?
• Bowels: a regimen in place

Not classical malignant hyperthermia. Boys with Duchenne or Becker dystrophy are not classically malignant-hyperthermia (RYR1) susceptible. What they are at high risk of is an anaesthesia-induced rhabdomyolysis with hyperkalaemic cardiac arrest, triggered by suxamethonium (succinylcholine) and the volatile anaesthetic agents. Clinically it can look MH-like: hyperkalaemia, rising end-tidal CO2, arrhythmia, dark myoglobinuric urine.

The anaesthetic. Avoid suxamethonium absolutely, because of the risk of hyperkalaemic arrest, and avoid or minimise volatile agents in favour of a total intravenous anaesthetic (TIVA) technique. Conditions with a genuine RYR1 link, central core disease for example, are truly MH-susceptible; any crisis is treated with dantrolene, cooling and management of the hyperkalaemia.

Not every curved spine in a child with disability is "simple" neuromuscular scoliosis. Distinguish the collapsing C-curve from mimics that change management.

The goal. A straight spine over a level pelvis, so that the patient can sit comfortably and be nursed.

Algorithm

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Neuromonitoring is routine in idiopathic scoliosis. The examiner wants you to know why it is different here.

Baseline signals are often unobtainable or unreliable. Many NMS patients (severe cerebral palsy, advanced DMD or SMA, myelomeningocele) have pre-existing motor and sensory deficits, so motor evoked potentials (MEPs) and somatosensory evoked potentials (SSEPs) may be absent or non-reproducible at baseline; in a substantial minority no usable trace can be obtained at all. The wake-up test is rarely feasible either, because of cognitive impairment and the inability to follow commands.

What that means. When signals are obtainable they remain valuable and should be used. When they are not, safety rests on meticulous technique: avoiding over-distraction across a rigid deformity, controlled correction, and accepting less-than-anatomic correction rather than risking the cord. Document the patient's monitorability pre-operatively and counsel the family.

The contrast with AIS. There, reliable MEP and SSEP monitoring is the expected standard, and a true alert mandates the rescue checklist (reduce correction, raise blood pressure, warm, recheck) or a wake-up test.

Quality of life. Parents report high satisfaction, primarily because of the ease of nursing care (transfers, bathing) and improved sitting tolerance. Correction of pelvic obliquity is the most impactful factor for sitting.

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Global Epidemiology:

• Scoliosis affects roughly a quarter of all children with cerebral palsy and the large majority of GMFCS IV-V (non-ambulant) children, with prevalence and severity rising with GMFCS level and age (Persson-Bunke, total-population data).
• Essentially all boys with Duchenne muscular dystrophy who lose ambulation develop scoliosis; historically up to 90% before routine glucocorticoid use. Long-term daily corticosteroids have markedly reduced both the incidence and severity of DMD scoliosis, so fewer patients now reach surgical thresholds.
• Spinal muscular atrophy (SMA) types I-II carry the highest and earliest scoliosis burden of the flaccid neuromuscular disorders.

Side-by-Side Guidance (where recommendations differ):

Quality of evidence. There are no randomised trials of spinal surgery in NMS (Cochrane, DMD). Practice rests on case series and physiological reasoning, so the magnitude of benefit on survival and quality of life is genuinely uncertain.

Fuse to the pelvis or stop at L5? Pelvic fixation reliably corrects obliquity but adds operative time, blood loss and the risk of S2AI or iliac complications. In ambulant CP with a level pelvis, stopping short of the pelvis can preserve motion; in non-ambulant patients with obliquity, the pelvis is included.

Unit Rod versus all-screw. All-pedicle-screw and S2AI constructs dominate modern practice, but no high-level trial proves superiority over the Unit Rod, which remains a cost-effective, well-validated option (Tsirikos: 68% curve and 71% obliquity correction).

Timing in DMD. Earlier surgery preserves a respiratory window, but glucocorticoids have reduced curve incidence/severity, so fewer boys now reach surgical thresholds and some are managed without fusion. The classic "fuse early, by 20-30 degrees" rule is being re-examined in the steroid era.

Growing constructs in SMA. Magnetically controlled growing rods reduce repeat lengthening surgeries but carry implant-related and infection risks, and intrathecal nusinersen access must be planned around any spinal construct.

BMP and graft choice. Osteopenic, low-volume local bone drives interest in BMP and allograft, but BMP is off-label in children and its safety profile in this population is not established.