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Muscular Dystrophy Scoliosis - Posterior Spinal Fusion (T2-Pelvis)

Surgical technique guide for Muscular Dystrophy Scoliosis - Posterior Spinal Fusion (T2-Pelvis) - FRCS exam preparation

Core Procedure
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High-yield overview

Posterior midline approach from upper thoracic spine (typically T2 or T3) to pelvis (S1 + bilateral iliac screws for pelvic fixation). | advanced

Critical Danger Structures - 5 Specific Zones

Spinal Cord

Location: Posterior in spinal canal, 2-3mm anterior to lamina

Protection: Avoid laminar violation during dissection, confirm all pedicle screws extra-canal with probe (all 4 walls), monitor SSEP/MEP during correction

Nerve Roots

Location: Exit through neural foramina below each pedicle, 2-5mm inferior to pedicle screw trajectory

Protection: Probe pedicle inferior wall to confirm no breach, avoid foraminal dissection, careful with L5 screws (steep trajectory)

Great Vessels

Location: Aorta 15-25mm anterior to vertebral body, vena cava 10-20mm anterior on right

Protection: Limit screw depth to measured pedicle length minus 5mm, fluoroscopy confirms no anterior breach, probe anterior wall resistance

Artery of Adamkiewicz

Location: Enters spinal canal T9-L2 (left side 80%), supplies anterior spinal cord

Protection: Maintain MAP >85 mmHg during correction, avoid aggressive osteotomies T9-L2, monitor SSEPs (ischemia indicator)

Superior Gluteal Artery

Location: Exits greater sciatic notch 2-3cm from PSIS, runs between iliac tables posteriorly

Protection: Iliac screw trajectory aims ANTERIOR (toward AIIS), not posterior, fluoroscopy confirms trajectory, avoid excessive posterior angulation

Mnemonic

SOLIDPELVIC FIXATION Requirements

Mnemonic

CARDIACDMD PREOP OPTIMIZATION Checklist

Patient Positioning

Position: Prone on Jackson table or chest rolls

  • Arms alongside body or on arm boards at <90° abduction (shoulder contractures)
  • Head in neutral or slight extension (avoid excessive flexion - airway compromise)
  • Chest rolls allow abdomen to hang free (reduces IVC compression, decreases venous bleeding)

Critical Padding Points (DMD has fragile skin, osteoporotic bones):

  • Forehead (avoid globe pressure)
  • Chest (chest rolls, avoid rib compression fractures)
  • Iliac crests (prominent, high pressure risk)
  • Knees and anterior shins
  • Arms and elbows

Monitoring Setup:

  • Neuromonitoring (SSEP, MEP) - note MEPs often poor/absent in DMD
  • Foley catheter (long surgery, fluid monitoring)
  • Arterial line (anticipated blood loss, tight BP control needed)
  • Core temperature monitoring

Clinical Pearl

Positioning Pearl: Check abdomen hangs free (reduces venous engorgement → less blood loss). DMD patients have fragile skin (pressure ulcer risk), osteoporotic ribs (fracture risk), contractures (limited ROM). Meticulous padding prevents complications in 5-8 hour surgery.

Surgical Exposure

Incision: Posterior midline from T2 spinous process to sacrum/upper buttock (40-50cm)

  • Incise skin, subcutaneous tissue (fatty in DMD - minimal muscle), posterior fascia
  • Plan for subcutaneous closure as main strength layer (muscle atrophy limits fascial closure)

Subperiosteal Dissection (T2 to pelvis):

  • Use Cobb elevator to strip paraspinal muscles off spinous processes, laminae, transverse processes bilaterally
  • Expose entire posterior elements: spinous processes, laminae, facets, transverse processes, pars
  • At pelvis: expose sacrum and posterior iliac wings bilaterally (for iliac screw insertion)
  • Place self-retaining retractors (Taylor, Schofield)

Exposure Risks

  • Excessive blood loss (long dissection, osteoporotic bone oozes, fatty tissue bleeds)
  • Use thrombin-soaked sponges, bipolar cautery, bone wax
  • Inadequate exposure leads to missed fusion levels or screw malposition

Complications - Recognition, Prevention, Management

Major Complications in DMD Scoliosis Surgery

Clinical Decision Scenarios

Use these scenarios to practise clinical reasoning and management decisions

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"A 14-year-old boy with Duchenne muscular dystrophy presents with progressive scoliosis. His curve is 35° (thoracolumbar), he is wheelchair-dependent, FVC is 45% predicted, and echo shows EF 35%. Would you offer surgery? What are the key considerations in timing?"

PRACTICAL APPROACH
This is a CLASSIC DMD scoliosis case at IDEAL timing for surgery. I WOULD offer surgery based on: (1) CURVE MAGNITUDE: 35° is in the sweet spot (30-50°). Too small (<20°) and surgery may be unnecessary. Too large (>70-80°) makes correction difficult and risks higher complications. (2) PROGRESSION: DMD curves are RELENTLESSLY progressive (typically 1-2° per month once >20°). Without surgery, he will develop severe curve (>80-100°), lose sitting balance, develop pelvic obliquity, worsen pulmonary function. (3) PULMONARY FUNCTION: FVC 45% is ADEQUATE (minimum is 30-40%, ideal >40%). As curve worsens, FVC drops (restrictive lung disease from chest wall deformity + muscle weakness). Operating at FVC 45% is safer than waiting until FVC <30% (prohibitive risk). (4) CARDIAC FUNCTION: EF 35% is BORDERLINE but acceptable (minimum EF is typically 30%). DMD develops progressive cardiomyopathy (dystrophin deficiency affects cardiac muscle). Need cardiology clearance and optimization (ACE inhibitors, beta-blockers). (5) FUNCTIONAL STATUS: Wheelchair-dependent is typical for DMD at this age (lose ambulation age 10-12). Surgery aims to preserve sitting balance and quality of life. KEY TIMING PRINCIPLE: Operate when curve 30-50°, FVC >40%, EF >30%, patient has reasonable quality of life. TOO EARLY (curve <20°, FVC >60%): Unnecessary surgery, may stabilize with bracing. TOO LATE (curve >70°, FVC <30%, EF <25%): Prohibitive risks (respiratory failure, cardiac complications, death). This patient is in the IDEAL WINDOW.
CLINICAL SCENARIOStandard

CLINICAL PROMPT

"Why is pelvic fixation mandatory in neuromuscular scoliosis, and how do you achieve it? What are the specific risks of iliac screw placement?"

PRACTICAL APPROACH
Pelvic fixation is MANDATORY in neuromuscular scoliosis (DMD, spina bifida, CP) due to: (1) PELVIC OBLIQUITY: Common in neuromuscular curves (pelvis tilts, causes asymmetric sitting, pressure sores, seating dysfunction). Fusion must extend to pelvis to correct/prevent pelvic obliquity. If stop at L5 or S1 alone, pelvic obliquity persists or recurs. (2) HIGH DEFORMITY FORCES: Neuromuscular patients have high forces on instrumentation (spasticity in CP, imbalanced muscles, poor bone quality, large curves). Stopping at S1 alone leads to SACRAL SCREW PULLOUT (failure rate up to 40% without iliac screws). S1 screws alone insufficient. (3) PSEUDARTHROSIS PREVENTION: Lumbosacral pseudarthrosis is high risk without pelvic fixation (motion at S1, high forces). Iliac fixation provides RIGID foundation, greatly reduces pseudarthrosis. HOW TO ACHIEVE PELVIC FIXATION: BILATERAL S1 SCREWS: Entry at S1 lateral mass, trajectory anterior/lateral toward sacral promontory. Large screws (7.5-8.5mm, 45-55mm). Bicortical if possible. BILATERAL ILIAC SCREWS (most critical component): Entry point at PSIS or 1-2cm caudal. Trajectory from PSIS toward AIIS (anterior inferior iliac spine). Screw runs between inner and outer tables of ilium. Long screws (70-100mm, 7.5-9.5mm diameter). Fluoroscopy: AP view shows screw parallel to iliac crest, lateral view shows caudal trajectory. OFFSET CONNECTORS: Link iliac screws to main rods (iliac screws sit lateral to rods). This creates a 4-point pelvic fixation (2 S1 + 2 iliac = SOLID foundation). RISKS OF ILIAC SCREWS: (1) ILIAC VESSEL INJURY: MEDIAL breach of iliac screw perforates inner table → hits iliac artery/vein (catastrophic bleeding). Prevention: aim trajectory ANTERIOR (PSIS → AIIS), not medial. Fluoroscopy confirms. (2) SUPERIOR GLUTEAL ARTERY: Exits greater sciatic notch 2-3cm from PSIS. At risk if screw trajectory too POSTERIOR or inferior. Prevention: aim ANTERIOR. (3) ABDOMINAL STRUCTURES: ANTERIOR cortex breach risks bowel, ureter. Prevention: limit depth to 70-100mm, fluoroscopy. (4) SCREW PROMINENCE: Iliac screws can be prominent posteriorly (skin breakdown risk). Prevention: countersink start hole, consider lower entry point.
CLINICAL SCENARIOStandard

CLINICAL PROMPT

"What is the role of neuromonitoring in scoliosis surgery, and what is your algorithm if there are SSEP changes during curve correction?"

PRACTICAL APPROACH
Neuromonitoring is STANDARD OF CARE in scoliosis correction surgery. Detects spinal cord injury BEFORE permanent damage occurs (allows intervention). TWO MODALITIES: (1) SSEP (Somatosensory Evoked Potentials): Monitors SENSORY pathways (dorsal columns - posterior spinal cord). Stimulate peripheral nerves (tibial, ulnar), record over sensory cortex. Measures amplitude and latency. Monitors posterior cord function. (2) MEP (Motor Evoked Potentials): Monitors MOTOR pathways (corticospinal tracts - lateral/anterior cord). Stimulate motor cortex, record over muscles (lower extremity: tibialis anterior, abductor hallucis). Monitors anterior cord function (most critical - motor deficit is devastating). Note: In DMD, MEPs often POOR or ABSENT at baseline (muscle weakness) - rely more on SSEPs. ALERT CRITERIA: SSEP changes: >50% amplitude drop OR >10% latency increase. MEP changes: >50% amplitude drop or complete loss. If SSEP/MEP CHANGES during correction, ALGORITHM: STEP 1: STOP all manipulation immediately (halt correction maneuvers, don't proceed). STEP 2: RELEASE compression/distraction (loosen construct if correction just applied, may need to back off some correction). STEP 3: NOTIFY anesthesia and surgical team (team awareness). STEP 4: OPTIMIZE spinal cord perfusion - Check BLOOD PRESSURE: Maintain MAP >85 mmHg (some recommend >90). Give fluids, pressors if needed (phenylephrine, norepinephrine). Cord ischemia from hypotension is reversible if caught early. STEP 5: WAIT for recovery (may take 10-20 minutes for signals to return if ischemic). Continue monitoring. STEP 6: If signals RECOVER: Proceed cautiously with less aggressive correction (accept less correction to preserve neuro function). If signals DON'T recover after 20-30 minutes: (a) Consider further RELEASE of construct (remove some screws, reduce rod tension), (b) Consider WAKE-UP TEST (Stagnara test - lighten anesthesia, ask patient to move hands/feet, confirms motor function), (c) If wake-up test shows deficit: ABORT correction (accept deformity, close, or convert to staged procedure). If wake-up test normal: monitoring false positive (rare but possible, proceed cautiously). STEP 7: If any doubt, err on side of SAFETY (better to undercorrect than cause paraplegia). INCIDENCE: Spinal cord injury <1% with neuromonitoring, but up to 0.5-1% without monitoring. Neuromonitoring is protective and standard of care.

DMD Scoliosis PSF (T2-Pelvis) - Exam Summary

Clinical summary

Evidence Base

Surgery for scoliosis in Duchenne muscular dystrophy (Cochrane systematic review)

Level I
Cheuk DKL, Wong V, Wraige E, Baxter P, Cole A • Cochrane Database of Systematic Reviews
Clinical Implication: Counsel families honestly: the benefits of fusion (seating, comfort, pelvic obliquity correction) are supported only by observational data, and there is no proof it prolongs life or preserves pulmonary function. This nuance is highly examinable.
Verify on PubMed (PMID 26423318)

Diagnosis and management of Duchenne muscular dystrophy, part 2: respiratory, cardiac, bone health, and orthopaedic management (DMD Care Considerations)

Guideline
Birnkrant DJ, Bushby K, Bann CM, et al. • The Lancet Neurology
Clinical Implication: The globally accepted framework for DMD work-up and the multidisciplinary peri-operative pathway underpinning safe spinal fusion in these patients.
Verify on PubMed (PMID 29395990)

Pelvic or lumbar fixation for the surgical management of scoliosis in Duchenne muscular dystrophy

Level III
Sengupta DK, Mehdian SH, McConnell JR, Eisenstein SM, Webb JK • Spine (Phila Pa 1976)
Clinical Implication: Pelvic fixation is mandatory once pelvic obliquity is established or the curve is large; early lumbar-only fixation is an option only in selected small flexible curves. Reinforces the value of operating before pelvic obliquity sets in.
Verify on PubMed (PMID 12634572)

Spinal fusion in Duchenne muscular dystrophy: a multidisciplinary approach

Level IV
Shapiro F, Sethna N, Colan S, Wohl ME, Specht L • Muscle & Nerve
Clinical Implication: Landmark evidence that the FVC decline continues post-operatively (it tracks muscle weakness, not the curve). The indication is seating/comfort and deformity prevention, not respiratory preservation.
Verify on PubMed (PMID 1584253)

Corticosteroids can reduce the severity of scoliosis in Duchenne muscular dystrophy

Level IV
Connolly AM, Kim HJ, Bridwell KH • The Journal of Bone and Joint Surgery (American)
Clinical Implication: Glucocorticoids are now standard of care and have changed who needs spinal surgery - fewer patients, often older. Always document steroid history (and its effect on bone quality and weight) when planning fusion.
Verify on PubMed (PMID 23783217)

References

  1. Suk SI, Lee SM, Chung ER, et al. Determination of distal fusion level with segmental pedicle screw fixation in single thoracic idiopathic scoliosis. Spine. 2003;28(5):484-491.

  2. Bridwell KH, Lenke LG, Baldus C, Blanke K. Major intraoperative neurologic deficits in pediatric and adult spinal deformity patients. Incidence and etiology at one institution. Spine. 1998;23(3):324-331.

  3. Yasui N, Aoki R, Nakazawa T, et al. Major complications of spinal surgery for patients with muscular dystrophy or spinal muscular atrophy: a multicenter study. J Orthop Sci. 2016;21(4):504-508.

  4. Bridwell KH, Baldus C, Iffrig TM, et al. Process measures and patient/parent evaluation of surgical management of spinal deformities in patients with progressive flaccid neuromuscular scoliosis (Duchenne's muscular dystrophy and spinal muscular atrophy). Spine. 1999;24(13):1300-1309.

  5. Altiok H, Finlayson C, Hassani S, et al. Neuromuscular scoliosis surgical outcomes in patients with Duchenne muscular dystrophy: a 20-year experience. J Pediatr Orthop. 2017;37(2):e94-e99.

  6. Garg S, Engel AJ, Grimm JC, et al. Pelvic fixation in neuromuscular scoliosis: comparison of different techniques. Spine. 2007;32(15):E423-E428.

  7. Barsdorf AI, Sproule DM, Kaufmann P. Scoliosis surgery in children with neuromuscular disease: findings from the US National Inpatient Sample, 1997 to 2003. Arch Neurol. 2010;67(2):231-235.

  8. Shapiro F, Sethna N, Colan S, et al. Spinal fusion in Duchenne muscular dystrophy: a multidisciplinary approach. Muscle Nerve. 1992;15(5):604-614.

  9. Sengupta DK, Mehdian SH, McConnell JR, et al. Pelvic or lumbar fixation for the surgical management of scoliosis in Duchenne muscular dystrophy. Spine. 2002;27(18):2072-2079.

  10. Miller DJ, Vitale MG, Skaggs DL, et al. Comparison of iliac screw versus S-alar-iliac screw pelvic fixation in patients with neuromuscular scoliosis. J Child Orthop. 2013;7(4):319-323.