FRCA Notes

Scoliosis Surgery

Resources

  • Scoliosis is a lateral curvature and rotation of the thoracolumbar vertebrae, with associated rib deformity
    • It can be defined as a Cobb angle (degree of the most tilted vertebrae on XR) >10%
    • It affects 2.5% of the population
    • It has a female preponderance (4x)

  • Patients presenting for corrective spinal surgery present over a spectrum of ages and with a range of comorbidities
  • 70 - 80% of cases are idiopathic, and described according to the age of onset:
    • Infantile (<4yrs)
    • Juvenile (4 - 9yrs)
    • Adolescent (10+yrs)
  • The remainder are owing to a variety of pathological conditions
Class Examples
Congenital Abnormal spinal cord or vertebral development
Neuropathy Cerebral palsy, syringomyelia, polio
Myopathy Muscular dystrophy, neurofibromatosis, Friedrich's ataxia
Mesenchymal Marfan's syndrome, RA, osteogenesis imperfecta
Malignancy Primary or secondary tumours
Trauma Fractures, post-surgical or post-radiotherapy
Infectious TB, osteomyelitis
Degenerative Osteoarthritis

Natural progression

  • Smaller curves may not progress, or even resolve
  • Larger curves (Cobb angle >30°) are more likely to progress
    • This leads to cosmetic deformity and back pain
    • Severe curves are accompanied by respiratory symptoms owing to restrictive lung defect
    • This can progress to pulmonary HTN and cor pulmonale

Indications

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

  • In juvenile or adolescent idiopathic patients, surgery is indicated to halt progression ± partially correct deformities
  • The aim is to prevent (further) respiratory or cardiovascular deterioration

  • In neuropathic scoliosis, severe curves may interfere with posture and sitting, so correction aims to improve general care

  • Adult, idiopathic curves tend to be slowly progressing and surgery is typically indicated for cosmetic improvements

Technique

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

  • Approach may be:
    • Posterior via single longitudinal incision in the prone patient (most common)

    • Anterior via thoracotomy
      • DLT and one-lung ventilation often not required
      • Typically for lumbar and thoracolumbar curves
      • May be the first stage of surgery ('anterior release') for thoracic, stiff or multiple curves prior to a posterior approach

    • Combined approach

Perioperative management of the patient undergoing corrective spinal surgery


  • History and examination should elucidate:
    • The aetiology of scoliosis
    • Location and degree of scoliosis
  • Pre-operative investigations and management focus on respiratory and cardiovascular sequelae of the disease

Respiratory

  • Establish:
    • Whether there is dyspnoea at rest
    • Frequency of respiratory tract infections
    • Strength of cough
    • Presence and degree of aspiration, especially in cerebral palsy
    • Presence of OSA

  • Patients with myopathy have a greater degree of pulmonary dysfunction for the equivalent angle
  • Pulmonary dysfunction is related to:
    • The degree of scoliosis (esp. once >100°)
    • Direction of the lateral curvature; curves are typically right-sided but left-sided curves are associated with higher likelihood of other comorbidities/congenital conditions
    • Number of vertebrae involved (typically 7 - 10)
    • The cephalad location of the curve
    • The degree to which the normal thoracic kyphosis is lost

  • Investigations
    • CXR

    • Pulmonary function tests
      • May identify restrictive lung defect
      • Reduced FEV1 and FVC but normal or increased FEV1/FVC ratio
      • Reduced VC, TLC and FRC (i.e. prone to hypoxia)
      • Residual volume typically maintained

    • ABG, which may demonstrate higher A-a gradient owing to V/Q mismatch
      • There is relatively increased apical blood flow in both lungs
      • Abnormal ventilation of the lung on the concave side of the curve

    • Sleep studies, which may indicate need for post-operative support if night-disordered breathing and/or dependence on CPAP

Cardiovascular

  • Cardiovascular disease may be related to either scoliosis (cor pulmonale) or underlying pathology (e.g. in muscular dystrophies)

  • Investigations
    • 12-lead ECG
    • TTE to assess:
      • LV function
      • Pulmonary artery pressures (cor pulmonale)
      • Valve function - mitral valve prolapse occurs in 25% of children with scoliosis

  • The aims of anaesthesia are to allow optimal surgical conditions, whilst simultaneously optimising physiology and facilitating neurophysiological monitoring to take place

Positioning

  • Posterior approach: prone
    • Normal meticulous approach to positioning applies, with particular reference to peripheral pressure areas and adequate chest/abdominal movement for ventilation
  • Anterior approach: lateral with convex side uppermost

Monitoring

  • AAGBI as standard
  • Invasive arterial blood pressure monitoring is mandatory, owing to a prolonged procedure with high propensity for significant blood loss
  • Wide-bore IV access x 2, or CVC if significant comorbidity
  • Urinary catheter
  • Temperature monitoring and management techniques
  • Depth of anaesthesia monitoring

Anaesthetic technique

  • Typically a TIVA technique to avoid interference of volatile anaesthesia with neurophysiological monitoring
  • Although small doses of NMBA are used to facilitate intubation, repeated doses aren't given due to interference with measuring CMAPs

Neurophysiological monitoring

  • MEPs, SSEPs and EMG are used
  • Continuous intra-operative spinal cord monitoring is employed, and provides an early marker of any compromise due to:
    • Direct nerve or spinal cord injury from instrumentation
    • Distraction injury
    • Reduced spinal cord perfusion and ischaemia

  • Wake up test (Stagnara)
    • Patient is briefly woken during surgery and asked to move their hands and feet, then immediately re-anaesthetised
    • Benefits from not requiring specialist equipment or personnel
    • However, it only demonstrates motor function at a single point in time
    • Not applicable in children or those with diminished cognitive capacity
    • Thought to still represent the gold standard

  • Overall, neurological complications are uncommon (0.3%)

Haemorrhage

  • Posterior approaches are associated with greater blood loss than the anterior approach
  • Group and cross match (two units)
  • Standard measures to prevent excessive haemorrhage apply:
    • Controlled hypotension (without compromising SCPP)
    • Cell salvage
    • TXA
    • Point-of-care testing i.e. visco-elastic haemostatic assays
    • Maintenance of normal temperature and pH

  • Typically cared for in an HDU area to allow continuous invasive monitoring and neurological assessments

Analgesia

  • High quality analgesia allows early mobilisation and physiotherapy
  • A multimodal approach should be employed:
    • Regular paracetamol
    • Regular NSAIDs - may be avoided due to fear of exacerbating bleeding or renal failure
    • IV (PCA) opioids, transitioned to oral opioids
    • Regional anaesthesia
      • E.g. epidural after anterior approach correction - NB need to ensure adequate neurological assessment prior to loading doses
      • E.g. paravertebral catheters
    • Perhaps unsurprisingly, infusing ketamine and dexmedetomidine are better than placebo at improving post-operative analgesia and sleep quality (BJA, 2023)

Respiratory support

  • Most patients are extubated at the end of the case, although post-operative atelectasis should be anticipated
  • Respiratory function is unlikely to improve immediately after scoliosis surgery
  • Early TWOC, mobilisation and physiotherapy can help

  • Post-operative ventilation may be required in some:
Patient factors Surgical factors
Pre-existing neuromuscular disorder Long duration/extent of surgery
Restrictive lung defect Invasion of the thoracic cavity
Cardiac involvement/right heart failure Blood loss >30ml/kg
Obesity Pneumothorax, haemothorax


  • Neurological complications (0.3%)
  • Post-operative pulmonary complications
    • FEV1 <40% or FVC <35% are predictive for prolonged post-operative ventilation
    • Hypoventilation
    • Atelectasis
    • Secretion retention
  • Post-operative visual loss due to ischaemic optic neuropathy or central retinal artery occlusion in prone position