FRCA Notes

Scoliosis Surgery

Curriculum

The most relevant curriculum item is knowing the perioperative care for: "Scoliosis surgery including the need for, and implications of, neurophysiological monitoring".

Examiner feedback

Despite voluminous BJA Education articles on the subject, the closest CRQ (March 2021, on spinal surgery) was not paediatric-specific and was well-answered (80% pass rate).

Resources

  • Scoliosis is a three-dimensional deformity of the spine: lateral curvature in the coronal plane with vertebral rotation and associated rib deformity
    • Defined as a Cobb angle (angle between the most tilted vertebrae on XR) >10°
    • Adolescent idiopathic scoliosis (AIS) affects 1 - 3% of adolescents
    • Curves >30° have a 5:1 female preponderance

  • Patients presenting for corrective surgery range from fit adolescents with idiopathic scoliosis to medically complex children with neuromuscular disease

  • ~80% of cases are idiopathic, described according to age of onset:
    • Infantile (<4yrs)
    • Juvenile (4 - 9yrs)
    • Adolescent (10+yrs); the most common

  • Early-onset scoliosis describes any curve with onset <10yrs
  • The remainder are secondary to a variety of conditions:
Class Examples
Congenital Abnormal vertebral or rib development, spinal dysraphism (e.g. myelomeningocele)
Neuropathic Cerebral palsy, spinal muscular atrophy, syringomyelia, Friedreich's ataxia, polio
Myopathic Duchenne muscular dystrophy, central core myopathy
Syndromic/mesenchymal Marfan's syndrome, neurofibromatosis, osteogenesis imperfecta, RA
Neoplastic Primary or secondary tumours
Traumatic Fractures, post-surgical or post-radiotherapy
Infective TB, osteomyelitis
Degenerative Osteoarthritis (adults)

Natural progression

  • Smaller curves may not progress, or may even resolve
  • Larger curves (Cobb angle >30°) are more likely to progress, leading to:
    • Cosmetic deformity, back pain and psychosocial distress
    • Restrictive lung defect with exertional dyspnoea (>65°)
    • Pulmonary HTN, cor pulmonale and respiratory failure (>100°)

  • Neuromuscular scoliosis starts earlier, is more severe and continues to progress after puberty
    • Bracing and seating adaptations may delay surgery but are unlikely to halt progression


Idiopathic Neuromuscular
Curve Smaller, flexible Large and rigid; pelvic obliquity and kyphosis common
Comorbidity Minimal Restrictive lung disease, cardiomyopathy, aspiration, epilepsy, poor nutrition
Airway and access Usually normal Difficult airway and IV access more likely
Intra-operative Haemodynamically stable on TIVA; reliable IONM CVS instability, vasopressor/inotrope use, hypothermia; poor IONM baselines
Blood loss Modest Greater; coagulopathy and massive transfusion more likely
Surgery Single-stage PSF, aiming for full correction Longer; pelvic fixation, osteotomies, possibly staged; correction may be compromised for safety
Post-operative Extubated in theatre; ward/HDU; short stay Often PICU ± ventilation; longer stay; higher complication rate
  • Neuromuscular patients have the highest complication rates (e.g. respiratory 12%, wound infection 13%)
  • Despite this, surgery improves pain, function, self-image and long-term mortality

Specific conditions

Condition Key anaesthetic considerations
Cerebral palsy Recurrent aspiration and chest infection; GMFCS IV - V have the most severe curves; subtle infection may only become apparent after induction
Duchenne muscular dystrophy Cardiomyopathy (echo may misrepresent function; cardiac MRI preferred); long-term steroids; suxamethonium contraindicated
Spinal muscular atrophy Bulbar and respiratory weakness, NIV dependence; limited mouth opening and neck movement
Central core myopathy RYR1 mutation leads to MH susceptibility; avoid volatiles & suxamethonium
Myelomeningocele Baseline neurological deficit; check VP shunt function; skin breakdown and wound infection


Indications

  • Surgery is indicated when the Cobb angle is >40 - 50°
    • >50° thoracic region
    • >40° lumbar region

  • The goals of surgery change slightly depending on the aetiology:
    • Idiopathic: halt progression, partially correct deformity and prevent cardiorespiratory deterioration
    • Neuromuscular: improve sitting, posture, care and pain and while FVC may not improve its rate of decline slows
    • Adult idiopathic curves progress slowly so surgery is often for cosmesis or pain

Technique

  • The spine is mobilised, the deformity corrected, then fused to maintain correction

  • Posterior spinal fusion (PSF) via a midline incision in the prone patient accounts for ~90%
    • Pedicle screws are attached to rods spanning the curve; the rods are rotated to realign the spine
    • Bone graft promotes fusion between vertebrae
    • May be performed under intra-operative skull femoral traction

  • Anterior approach via thoracotomy/thoraco-abdominal incision
    • One-lung ventilation rarely required except for high thoracic curves
    • Relatively uncommon as single-stage posterior procedures are favoured due to reduced theatre time and length of stay

  • Early-onset scoliosis: growing rods control deformity while allowing thoracic growth and lung development
    • Requires repeated lengthening procedures every 6 months

Perioperative Management of the Patient Undergoing Corrective Spinal Surgery


  • Pre-assessment at least 2 weeks before surgery
    • Complex/neuromuscular patients should be assessed via an MDT clinic
    • Spinal surgeon, anaesthetist, cardiology, respiratory, paediatrics, physiotherapy and OT

  • History and examination should establish the aetiology, location and severity of the curve, functional status and previous anaesthetic history
  • Discuss the plan (lines, analgesia, post-operative destination, transfusion consent); this reduces anxiety and improves satisfaction

Respiratory

  • Establish:
    • Exercise tolerance and dyspnoea at rest
    • Frequency of chest infections and strength of cough
    • Aspiration risk, especially in cerebral palsy
    • OSA, sleep-disordered breathing and NIV use

  • Pulmonary dysfunction worsens with:
    • Greater curve angle (especially >100°)
    • More vertebrae involved and more cephalad curves
    • Loss of normal thoracic kyphosis
    • Left-sided curves (associated with other congenital conditions)
    • Underlying myopathy, which causes greater dysfunction for an equivalent angle

  • Investigations
    • CXR
    • Pulmonary function tests (often not possible in neuromuscular patients)
      • Restrictive defect: reduced FEV1 and FVC with normal or increased FEV1/FVC ratio
      • Reduced VC, TLC and FRC (i.e. prone to hypoxia); RV typically maintained
    • ABG: raised A-a gradient from V/Q mismatch
    • Sleep studies: identify need for (or adjustment of) NIV
    • Cough peak flow (>12yrs): <270 L/min suggests need for cough augmentation

  • Optimisation: physiotherapy, secretion clearance, hyperinsufflation, treatment of infection

Cardiovascular

  • Disease may relate to the scoliosis (cor pulmonale) or the underlying condition (e.g. cardiomyopathy in muscular dystrophy)
  • Investigations:
    • 12-lead ECG
    • TTE to assess LV function, pulmonary artery pressure and valves (mitral valve prolapse in ~25%)
    • Cardiac MRI where echo windows are poor or may underestimate dysfunction (e.g. DMD)
  • Symptomatic heart failure or LVEF <30% carries the highest perioperative risk
  • Pacemakers/ICDs need checking and reprogramming plans

Neurological

  • Document any baseline neurological deficit
  • Optimise antiepileptic medication
  • Note spasticity treatments e.g. baclofen (including intrathecal pumps)

Haematological

  • Pre-operative anaemia increases transfusion risk and length of stay; investigate and treat
  • FBC, coagulation and cross-match

Nutritional and metabolic

  • Dietician input for low or high BMI
  • Osteoporosis (immobility, steroids): bisphosphonates reduce fracture risk during positioning
  • Long-term steroids require perioperative supplementation
  • Neuromuscular patients are prone to hypoglycaemia (low muscle mass): minimise fasting and place first on the list

Psychological

  • Pre-operative anxiety affects 75 - 80% of AIS patients
  • Pre-operative pain, anxiety and pain catastrophising predict chronic post-surgical pain

  • The aims of anaesthesia are to provide optimal surgical conditions while maintaining spinal cord perfusion and facilitating neurophysiological monitoring

Induction and airway

  • Neuromuscular patients may be very sensitive to sedative premedication
  • IV or inhalational induction are both acceptable
  • Plan for a difficult airway in neuromuscular disease (contractures, limited mouth opening, fixed cervical spine) and increased secretions/aspiration risk
  • Consider replacing an existing tracheostomy with a tracheal tube for the duration of surgery

  • A small dose of non-depolarising NMBA (e.g. rocuronium 0.2 - 0.4 mg/kg) facilitates intubation; avoid further doses
  • Avoid suxamethonium in muscular dystrophies (hyperkalaemic cardiac arrest) and central core myopathy (MH)

Monitoring and access

  • Association of Anaesthetists standard monitoring
  • Invasive arterial monitoring is mandatory: prolonged procedure with potential for major haemorrhage
  • Two wide-bore IV cannulae; CVC if significant comorbidity or poor peripheral access
  • Urinary catheter and temperature monitoring
  • Depth of anaesthesia: BIS, or raw EEG from the neurophysiologist
  • ± Cardiac output monitoring to guide goal-directed fluid therapy

Positioning

  • Posterior approach: prone on a frame (e.g. Wilson/four-poster) allowing free abdominal movement
    • Improves ventilation and avoids IVC compression, which would increase epidural venous bleeding
    • Head neutral, eyes free of pressure, arms not abducted >90°
    • Meticulous padding of pressure areas, especially in neuromuscular patients (contractures, low muscle mass, gastrostomies, baclofen pumps)
    • Ventilation or cardiovascular compromise may require a return to supine so keep a trolley available

  • Anterior approach: lateral with convex side uppermost

Anaesthetic technique

  • TIVA (propofol and remifentanil) to minimise interference with neurophysiological monitoring
  • Volatile agents and nitrous oxide are avoided (see below)
  • Ketamine infusion may be added as an analgesic adjunct

Temperature and infection

  • Long induction to incision time (lines, IT morphine, traction, positioning) predisposes to hypothermia
  • Pre-warm with forced-air blankets; warm theatre, fluids and forced-air warming intra-operatively
  • Maintain 36 - 38°C to reduce surgical site infection (up to 7% in AIS)

  • Antibiotic prophylaxis (e.g. cefazolin) within 60 min of incision, re-dosed every 4 h

Fluids

  • Hypovolaemia and fluid overload are both harmful so goal-directed fluid therapy may be used as a balanced approach
  • Neuromuscular patients often receive large crystalloid volumes (~40 ml/kg), risking oedema, SIADH and AKI so early low-dose vasopressor is common

Haemorrhage

  • Typical AIS blood loss ~300 - 900 ml/li>
    • Greater blood loss in those with neuromuscular disease aetiology
    • Rigid curves, osteotomies, pelvic fixation, osteopenic bone and poor platelet function are associated with greater loss
    • Massive loss associated with >12 levels fused, low BMI and long operating time

  • Blood conservation:
    • Pre-operative anaemia management and cross-match
    • TXA: e.g. 10 - 50 mg/kg load then 10 mg/kg/h (give slowly as high doses risk seizures)
    • Cell salvage: routine in neuromuscular surgery, often unnecessary in AIS
    • Prone positioning without abdominal compression
    • Maintenance of normothermia and normal pH
    • Point-of-care testing (visco-elastic haemostatic assays)
    • Controlled hypotension only if spinal cord perfusion is not compromised (see below)

PONV prophylaxis

  • Dexamethasone and ondansetron
  • Oral aprepitant (NK1 antagonist) pre-operatively is a useful adjunct in high-risk patients

  • New neurological deficit occurs in 0.3 - 2%, owing to:
    • Direct cord or nerve root injury from instrumentation
    • Distraction injury (e.g. traction, curve correction)
    • Reduced spinal cord perfusion and ischaemia
  • Continuous intra-operative neuromonitoring (IONM) gives early warning and is standard of care; see also neurophysiological monitoring

Spinal cord blood supply

  • Single anterior spinal artery: anterior two-thirds (corticospinal tracts and motor neurones)
  • Paired posterior spinal arteries: posterior third (dorsal columns)
  • Limited collateral flow between the two, so the motor pathway is especially vulnerable to hypotension and stretch of the anterior spinal artery

Modalities

Modality Pathway monitored Key points
SSEPs Dorsal columns: peripheral nerve stimulated, cortical response recorded Requires averaging (delay); poor sensitivity for motor injury; resistant to hypotension
MEPs Corticospinal tracts: transcranial stimulation, muscle CMAP recorded Sensitive to ischaemia and change earlier than SSEPs; abolished by NMB; less reliable <6yrs; bite block needed
EMG Nerve roots: free-running or triggered via pedicle screws Detects screw misplacement; requires no NMB
EEG Cerebral cortex Guides depth of anaesthesia
  • No consensus on alert thresholds; commonly MEP amplitude reduction >60% or SSEP amplitude reduction 50%/ latency increase 10% are used

Factors affecting signals

Factor Effect
Volatile agents Dose-dependent reduction in MEP amplitude
Nitrous oxide Most profound depression of SSEPs and MEPs
Propofol Less effect than volatiles at equipotent doses; accumulation causes 'anaesthetic fade'
Ketamine Increases SSEP and MEP amplitude; makes EEG/BIS unreliable
Opioids (including IT morphine) Minimal clinical effect
Benzodiazepines, IV lidocaine Compatible
NMBA Abolishes MEPs
Dexmedetomidine, clonidine Reduce MEP amplitude; use with caution
Hypotension MEPs degrade once MAP <60 mmHg; SSEPs relatively resistant
Hypoxaemia, hypocapnia, hypothermia Degrade signals

  • Maintain a steady state and communicate any drug changes to the neurophysiologist
  • Titrating propofol to EEG minimises anaesthetic fade and prolonged emergence

Response to an IONM alert

  • Surgeon: pause, and reverse the last manoeuvre (e.g. reduce traction, remove/reposition implant)
  • Anaesthetist: increase MAP as first-line therapy, then optimise:
    • Oxygenation, Hb and normocapnia
    • Temperature
    • Recent drug or depth of anaesthesia changes
    • Positioning (e.g. brachial plexus stretch)
  • Neurophysiologist: exclude technical causes
  • If unresolved: consider wake-up test, steroids, and limiting the extent of surgery

Wake-up test (Stagnara)

  • Patient briefly woken and asked to move hands and feet, then re-anaesthetised
  • Requires no specialist equipment
  • However:
    • Only a snapshot of motor function at a single point in time
    • Requires a cooperative patient; not possible in young children or cognitive impairment
    • Risk of accidental extubation and line loss
  • Largely superseded by continuous IONM; reserved for unresolved signal changes

  • Posterior spinal fixation is among the most painful paediatric procedures (mean pain score ~6.6/10 on day 1)
  • Poor control delays mobilisation and oral intake and prolongs length of stay
  • Chronic post-surgical pain affects up to 50% at 1 year; predicted by pre-operative pain and high opioid use on day 1
  • A multimodal, opioid-sparing approach is used; no single optimal combination has been established
Analgesia Key points
Paracetamol Regular dosing reduces opioid use, opioid side-effects and length of stay
NSAIDs Reduce pain and opioid use; no increase in pseudoarthrosis or bleeding shown in children
Intrathecal morphine Given after induction or by the surgeon
lasts 12 - 18hrs
Low/moderate dose (≤19 mcg/kg) is effective
Higher doses add respiratory depression without benefit
IV opioid PCA/NCA Mainstay; aim to stop within 24hrs and convert to oral
Epidural analgesia Small benefit up to 72hrs; high rates of failure (up to 37%) and catheter migration
Remifentanil Possible dose-dependent acute opioid tolerance although this is attenuated by IT morphine
Ketamine Reduces pain after spinal surgery generally although benefit in AIS unproven
Gabapentin Effective when started pre-operatively and continued; a single dose is ineffective
Methadone Long-acting with NMDA antagonism so reduces opioid use (off-label)
IV lidocaine, dexmedetomidine Limited paediatric evidence (off-label)
Dexmedetomidine reduces MEPs so is better reserved for post-operative use
Erector spinae plane block Bilateral ± bilevel; reduces pain, opioid use and PONV with no effect on IONM
  • Infusing ketamine and dexmedetomidine improved post-operative analgesia and sleep quality compared with placebo (BJA, 2023)
  • Non-pharmacological measures (education, CBT, distraction) may help but evidence is limited
  • Neuromuscular patients: adjust doses for low BMI, opioid sensitivity, sleep-disordered breathing and renal function; pain often assessed by carers

  • Most AIS patients are extubated in theatre, allowing early neurological assessment, then cared for on HDU
  • Neuromuscular patients frequently go to PICU, often still intubated for stabilisation and daytime extubation
    • Extubate onto home NIV if established; also use NIV if VC <60% predicted or cough is ineffective

  • Post-operative ventilation may be required in some:
Patient factors Surgical factors
Neuromuscular disorder Long duration/extent of surgery
Restrictive lung defect (FEV1 <40% or FVC <35%) Invasion of the thoracic cavity
Cardiac involvement/right heart failure Blood loss >30 ml/kg or massive transfusion
Obesity Pneumothorax, haemothorax
Previous respiratory illness requiring PICU Metabolic acidosis

Enhanced recovery

  • ERAS pathways reduce pain and length of stay without increasing complications or readmissions
  • Typical milestones:
    • Day 0: PCA (no background if IT morphine given), regular paracetamol and NSAID, antiemetics, laxatives
    • Day 1: long-acting oral opioid, remove urinary catheter, sit/stand with physiotherapy, solid diet
    • Day 2: stop PCA and IV drugs, short-acting oral opioids, ambulate on the ward
  • Early PCA discontinuation and mobilisation reduce ileus and atelectasis

Fluids and bloods

  • Ongoing blood loss and ileus are common
  • SIADH may reduce urine output; avoid hypotonic fluids and monitor sodium
  • Repeat FBC, coagulation and electrolytes

Neurological

  • New deficit (0.3 - 2%) from direct injury, distraction or ischaemia
  • Peripheral nerve injury from positioning

Respiratory

  • Hypoventilation, atelectasis, secretion retention and pneumonia
  • Most common major complication in neuromuscular patients

Prone position

  • Post-operative visual loss (ischaemic optic neuropathy, central retinal artery occlusion)
  • Pressure injuries, facial and airway oedema
  • Tube or line displacement

Other

  • Massive haemorrhage and coagulopathy
  • Surgical site infection
  • PONV, ileus and constipation
  • SIADH and AKI
  • Chronic post-surgical pain
  • Pseudoarthrosis and implant failure