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Selective Dorsal Rhizotomy (SDR) for Spastic Cerebral Palsy

Surgical technique guide for Selective Dorsal Rhizotomy (SDR) for Spastic Cerebral Palsy - FRCS exam preparation

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High Yield Overview

SELECTIVE DORSAL RHIZOTOMY (SDR) FOR SPASTIC CEREBRAL PALSY

Posterior midline approach to lumbosacral spine, L1 to S1 levels. Single-level laminectomy at L1-L2 or multi-level mini-laminoplasty | advanced

Critical Danger Structures

Conus Medullaris

Location: Typically ends at L1-L2 but can extend to L3 in children, 2-3mm posterior to dura

Protection: Identify with ultrasound/fluoroscopy before laminectomy; perform laminectomy at or below conus termination

Injury Risk: Bladder/bowel dysfunction, lower limb paralysis

Cauda Equina Nerve Roots

Location: L2-S5 nerve roots, 1-2mm diameter each, travel obliquely caudad within thecal sac to exit foramina

Protection: Gentle microsurgical technique, avoid excessive traction, maintain CSF cushion with irrigation

Injury Risk: Permanent motor/sensory deficit in root distribution

Anterior Spinal Artery

Location: 5-7mm ventral to cord in anterior median sulcus, supplies anterior 2/3 of spinal cord

Protection: Stay posterior to nerve roots, avoid ventral dissection, never manipulate anterior dura

Injury Risk: Anterior cord syndrome with bilateral motor loss

Artery of Adamkiewicz

Location: Enters typically T9-L2 (usually left side), main feeder to anterior spinal artery

Protection: Minimize manipulation of upper lumbar roots, avoid excessive cautery near radicular arteries

Injury Risk: Spinal cord ischemia, paraplegia

Ventral (Motor) Roots

Location: ANTERIOR to dorsal roots, THICKER (2-3mm vs 1-2mm), run obliquely anteriorly to exit foramina

Protection: Meticulous identification of all roots before division, use EMG to confirm dorsal vs ventral

Injury Risk: Permanent weakness in muscle territory supplied (if >2% risk = technical error)

Mnemonic

SPASTICSDR Patient Selection - SPASTIC

Mnemonic

BRIEFEMG Response Grading - BRIEF

Absolute Indications

Primary Diagnosis

  • Spastic diplegia cerebral palsy (bilateral lower limb involvement)
  • GMFCS Level II-III (ambulatory with or without aids)
  • Age 3-8 years (flexible: some centers 2-10 years)

Functional Criteria

  • Spasticity predominates over weakness (Modified Ashworth Scale ≥2)
  • Dynamic spasticity (improves with nerve blocks, sleep)
  • Good selective motor control
  • Adequate trunk control and upper limb function
  • Motivated child and family

Failed Conservative Management

  • Intensive physiotherapy (minimum 12 months)
  • Appropriate orthoses (AFOs, KAFOs)
  • Botulinum toxin injections (multiple cycles)
  • Oral anti-spasmodics (baclofen, diazepam)
  • No fixed contractures or minimal contractures that can be addressed with orthopaedic surgery post-SDR

Relative Indications

  • Spastic quadriplegia with good upper limb function (carefully selected)
  • Older children (8-12 years) with preserved motor control
  • Combined SDR with orthopaedic procedures for mild contractures

Contraindications

Absolute Contraindications

  • Dystonia or athetosis (will not improve with SDR, may worsen)
  • Severe weakness predominating over spasticity
  • Fixed contractures requiring extensive orthopaedic surgery first
  • Poor trunk control (GMFCS IV-V)
  • Cognitive impairment preventing rehabilitation participation
  • Spine deformity (severe scoliosis, kyphosis >40°)
  • Previous spine surgery with extensive fusion

Relative Contraindications

  • Hip instability or subluxation (address orthopaedically first)
  • Seizure disorder (poorly controlled)
  • Severe behavioral issues preventing intensive physiotherapy
  • Unrealistic family expectations
  • Age <2 years (spasticity pattern not established)
  • Age >12 years (neuroplasticity reduced)

Pre-operative Assessment

Clinical Assessment

  • Complete neurological examination
  • Modified Ashworth Scale (spasticity grading)
  • Selective motor control testing
  • Range of motion (passive vs active)
  • Muscle strength (MRC grading)

Gait Analysis

  • 3D motion analysis with kinematics
  • Electromyography during gait (identify overactive muscles)
  • Ground reaction force patterns
  • Energy expenditure measurement
  • Video recording for comparison

Imaging

  • Spine MRI (exclude tethered cord, syrinx, Chiari malformation)
  • Hip radiographs (assess migration percentage)
  • Lower limb alignment films (if needed)

Functional Assessment

  • GMFCS level documentation
  • Functional Mobility Scale (FMS)
  • Pediatric Quality of Life Inventory
  • Caregiver burden assessment

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

EXAMINER

"A 5-year-old child with spastic diplegic cerebral palsy is referred for consideration of SDR. Walk me through your assessment and selection criteria."

EXCEPTIONAL ANSWER
I would perform a comprehensive assessment to determine if SDR is appropriate. First, I confirm the diagnosis is spastic diplegia, not dystonia or athetosis, as SDR is only effective for spasticity. I assess the child's GMFCS level - ideal candidates are level II-III who can ambulate independently or with aids. I verify the age range of 3-8 years, though this is somewhat flexible. I examine the child to ensure spasticity predominates over weakness - I look for Modified Ashworth Scale ≥2 and assess selective motor control. I confirm adequate trunk control and upper limb function. I review conservative treatment - they should have had intensive physiotherapy, appropriate orthoses, and multiple cycles of botulinum toxin without sufficient improvement. I arrange 3D gait analysis to quantify the spasticity distribution and identify specific muscle groups contributing to gait abnormalities. I obtain spine MRI to exclude tethered cord, syrinx, or Chiari malformation. I assess the child and family's motivation and ability to participate in intensive post-operative rehabilitation. If all criteria are met, I discuss realistic expectations with the family - SDR reduces spasticity but doesn't cure CP, and intensive therapy is required to capitalize on the tone reduction.
VIVA SCENARIOStandard

EXAMINER

"Intraoperatively during SDR, you stimulate a rootlet and get a sustained bilateral response in both gastrocnemius muscles lasting 5 seconds. What is your interpretation and management?"

EXCEPTIONAL ANSWER
This is a Grade 4 EMG response - the most abnormal pattern. It demonstrates sustained muscle contraction with bilateral spread, which is characteristic of rootlets contributing to spasticity. This rootlet should be divided. A normal rootlet would show a brief, localized twitch that fatigues rapidly (Grade 0-1). The sustained bilateral response indicates this rootlet has abnormal reflex connections in the spinal cord that are maintaining the spastic pattern. Given this is in the gastrocnemius territory, this is likely an S1 dorsal rootlet, which is the most important level for treating equinus (toe-walking). I would mark this rootlet for division. S1 is treated aggressively with 40-60% of abnormal rootlets divided because gastrocnemius spasticity is the primary driver of toe-walking in diplegic CP. I would ensure I'm testing the dorsal root - the ventral S1 root would also cause gastrocnemius contraction when stimulated but is ANTERIOR and THICKER and must never be divided. I systematically test all S1 rootlets and divide those showing Grade 3-4 responses until I've achieved 40-60% division while preserving enough rootlets for sensory function.
VIVA SCENARIOStandard

EXAMINER

"You are 6 months post-op from SDR in a 6-year-old. The child has excellent tone reduction but the parents report progressive roundback deformity and back pain. What is your concern and management?"

EXCEPTIONAL ANSWER
My primary concern is post-laminectomy kyphosis, which occurs in 10-15% of SDR patients with modern single-level laminectomy technique (higher 20-25% with traditional multi-level laminectomy). This occurs because the posterior tension band of the spine has been disrupted by removal of the lamina, spinous process, and potentially the interspinous ligaments, leading to progressive flexion deformity. I would examine the child's spine clinically - looking for visible roundback deformity, measuring the sagittal contour, checking for tenderness and assessing if the deformity is flexible or fixed. I would obtain standing lateral radiographs of the entire spine to measure the kyphosis angle - normal thoracolumbar junction is slightly kyphotic but should be <20 degrees. I would classify the kyphosis severity and determine if it's progressive by comparing to any prior films. For mild curves <40 degrees that are asymptomatic, I would observe with physiotherapy focusing on core and paraspinal muscle strengthening, consider a TLSO brace to prevent progression, and monitor with serial radiographs every 6 months. For progressive curves >40-50 degrees or symptomatic kyphosis with pain, I would refer to pediatric spine surgery for consideration of posterior spinal fusion with instrumentation. I would counsel the family that this is a known complication of SDR - the risk is minimized by single-level laminectomy but can't be completely eliminated. Prevention strategies include limiting bone removal and preserving facet joints, which I would have done at the index procedure.

SDR for Spastic Cerebral Palsy - Exam Summary

High-Yield Exam Summary

References

  1. Peacock WJ, Arens LJ. Selective posterior rhizotomy for the relief of spasticity in cerebral palsy. South African Medical Journal. 1982;62(5):119-124.

    • Landmark paper describing the original SDR technique and patient selection criteria

  2. Park TS, Johnston JM. Surgical techniques of selective dorsal rhizotomy for spastic cerebral palsy. Technical note. Neurosurgical Focus. 2006;21(2):e7.

    • Detailed technical description of modern SDR technique with single-level laminectomy approach

  3. Grunt S, Fieggen AG, Vermeulen RJ, et al. Selection criteria for selective dorsal rhizotomy in children with spastic cerebral palsy: a systematic review of the literature. Developmental Medicine & Child Neurology. 2014;56(4):302-312.

    • Comprehensive systematic review of patient selection criteria and outcomes

  4. Tedroff K, Löwing K, Åström E. A prospective cohort study investigating gross motor function, pain, and health-related quality of life 17 years after selective dorsal rhizotomy in cerebral palsy. Developmental Medicine & Child Neurology. 2015;57(5):484-490.

    • Long-term outcomes study demonstrating sustained benefits of SDR at 17-year follow-up

  5. Langerak NG, Lamberts RP, Fieggen AG, et al. A prospective gait analysis study in patients with diplegic cerebral palsy 20 years after selective dorsal rhizotomy. Journal of Neurosurgery: Pediatrics. 2008;1(3):180-186.

    • 20-year follow-up gait analysis demonstrating maintained improvements in spasticity and function

  6. Ailon T, Beauchamp R, Miller S, et al. Long-term outcome after selective dorsal rhizotomy in children with spastic cerebral palsy. Child's Nervous System. 2015;31(3):415-423.

    • Multi-center study of long-term outcomes including complications (kyphosis, sensory changes)

  7. Munger ME, Aldahir BM, Miller PE, et al. Spinal deformity after selective dorsal rhizotomy in ambulatory patients with cerebral palsy. Journal of Neurosurgery: Pediatrics. 2017;20(5):453-459.

    • Analysis of spinal deformity rates comparing single-level vs multi-level laminectomy techniques

  8. Engsberg JR, Ross SA, Wagner JM, Park TS. Changes in hip spasticity and strength following selective dorsal rhizotomy and physical therapy for spastic cerebral palsy. Developmental Medicine & Child Neurology. 2002;44(4):220-226.

    • Study examining the relationship between spasticity reduction and strength gains post-SDR

  9. Farmer JP, Sabbagh AJ. Selective dorsal rhizotomies in the treatment of spasticity related to cerebral palsy. Child's Nervous System. 2007;23(9):991-1002.

    • Comprehensive review of SDR indications, techniques, and outcomes with emphasis on neurophysiological monitoring

  10. Dudley RW, Parolin M, Gagnon B, et al. Long-term functional benefits of selective dorsal rhizotomy for spastic cerebral palsy. Journal of Neurosurgery: Pediatrics. 2013;12(2):142-150. Long-term functional outcome study demonstrating GMFCS improvements and quality of life benefits