Posterior midline approach with subperiosteal exposure of the laminae, facets and transverse processes, segmental pedicle-screw instrumentation across the structural curves, and selective fusion guided by the Lenke classification.
- The Lenke classification determines fusion levels: six curve types, a lumbar modifier (A/B/C) based on the apex-to-CSVL relationship, and a sagittal modifier (minus/N/plus) based on T5 to T12 kyphosis.
- Pedicle screw entry points differ by region: thoracic is the lateral-superior quadrant of the facet; lumbar is the facet to transverse-process junction. Trajectory converges 10 to 15 degrees medially and stays parallel to the superior endplate.
- Neuromonitoring is mandatory. MEP and SSEP alarm criteria are a greater than 50 percent amplitude drop or a greater than 10 percent latency increase; an isolated MEP drop suggests motor-pathway or cord injury.
- Proximal junctional kyphosis (PJK) is the most common long-term complication (10 to 30 percent), so upper instrumented vertebra (UIV) selection is critical, avoiding the apex of thoracic kyphosis.
- A curve is structural when its Cobb angle is greater than 25 degrees and it corrects by less than 25 degrees on side-bending films; only structural curves are fused, sparing mobile segments.
- “Bending films separate structural from flexible curves. Structural curves correct by less than 25 degrees on bending; flexible curves correct by more than 25 degrees.
- “The lowest instrumented vertebra (LIV) should be the stable vertebra (bisected by the centre sacral vertical line, CSVL) or the neutral vertebra, to prevent distal adding-on.
- “Four-wall palpation of every pedicle tract is mandatory. A medial breach risks catastrophic spinal cord injury.
- “Rod derotation corrects the three-dimensional deformity: rotate the concave rod posteriorly to translate apical vertebrae toward the midline and reduce the rib hump.
When & Why
Indications. Posterior spinal fusion is offered for adolescent idiopathic scoliosis (AIS) when the deformity is large enough, or progressive enough, to threaten adult function or cosmesis. - Absolute indications: Cobb angle greater than 45 to 50 degrees (the SRS surgical threshold); documented progression greater than 5 degrees over six months despite orthotic management; skeletally mature patients (Risser 4 to 5) with curves greater than 40 degrees and unacceptable trunk imbalance; thoracic curves greater than 50 degrees, which carry a high risk of adult progression (around 1 degree per year in natural-history studies).
- Relative indications: thoracolumbar or lumbar curves greater than 40 to 45 degrees with coronal imbalance (C7 plumb line more than 2 cm from the CSVL); double major curves with both components greater than 40 degrees; 40 to 50 degree curves in growing patients (Risser 0 to 3) that progress despite bracing; curves with significant sagittal plane deformity. Contraindications. Absolute: active spinal infection (treat first); uncontrolled cardiopulmonary comorbidity precluding safe anaesthesia; uncorrectable bleeding diathesis; patient or family refusal after informed consent. Relative: severe osteopenia or osteoporosis (Z-score less than minus 2.5, poor screw purchase, consider cement augmentation); malnutrition (albumin less than 3.5 g/dL); obesity (BMI greater than 35, higher infection and wound risk); age less than 10 with an open triradiate cartilage (crankshaft risk, consider growth-friendly constructs); neuromuscular scoliosis, which is not true AIS and carries different considerations. Assess the whole patient, not just the Cobb angle. Before committing, exclude red flags that change the plan: - Pain or neurological symptoms are uncommon in true AIS. Their presence demands an MRI to look for a syrinx, tumour or tethered cord.
- A whole-spine MRI is mandatory in all presumed AIS before surgery. Chiari malformation is found in around 20 percent, syringomyelia and tethered cord are common, and MRI abnormalities turn up in 5 to 10 percent of presumed AIS cases.
- Respiratory symptoms or a curve greater than 70 degrees warrant pulmonary function tests; FVC and FEV1 fall by about 0.6 percent per degree above 50 degrees, and severe restriction (FVC less than 40 percent predicted) raises perioperative respiratory risk.
- Skin signs (cafe-au-lait spots, a midline hairy patch or sinus) suggest neurofibromatosis or occult spinal dysraphism. The one decision that drives the operation: which curves to fuse. Fusion is selective. Only structural curves are fused; flexible compensatory curves are left to correct spontaneously. Selection rests on standing PA and lateral 36-inch films plus supine side-bending films: - UIV (upper instrumented vertebra): the upper end vertebra of the main structural curve, or the proximal stable vertebra, typically T2 to T4 for a main thoracic curve. Stopping too low, or at the apex of thoracic kyphosis, invites proximal junctional kyphosis.
- LIV (lowest instrumented vertebra): the stable vertebra (bisected by the CSVL) or, failing that, the neutral vertebra (most closely bisected by the CSVL). Stopping too short invites distal adding-on; stopping too long sacrifices lumbar motion. The full Lenke classification system, which underpins this decision, is detailed in Background & Evidence below. Consent specifically for neurological injury (0.5 to 1 percent, permanent paralysis 0.1 to 0.5 percent), surgical site infection (3 to 5 percent overall), blood loss requiring transfusion (30 to 50 percent), pseudarthrosis (2 to 5 percent), proximal junctional kyphosis (10 to 30 percent), implant failure (1 to 2 percent), and the permanence of fusion (loss of motion at fused segments). Benefits are curve correction of 50 to 70 percent, halted progression, and improved cosmesis and self-image, with satisfaction of 80 to 90 percent.
The Operation
The goal: through a single posterior midline incision, expose the posterior elements subperiosteally across the planned levels, place segmental pedicle screws at every level, decorticate a fusion bed, then use contoured rods with compression, distraction and derotation to correct the three-dimensional deformity, and finally graft and close. The exposure is the foundation of everything that follows and is laid out in full as the first steps below.
Posterior spinal fusion — operative sequence
- General endotracheal anaesthesia with large-bore access and an arterial line. Use total intravenous anaesthesia (TIVA with propofol and remifentanil): avoid neuromuscular blockade after intubation (it abolishes MEPs) and keep volatile agents below 1 MAC.
- Tranexamic acid for blood conservation: 10 to 15 mg/kg loading dose, then 1 mg/kg/hr until closure (reduces blood loss 30 to 50 percent). Maintain MAP greater than 65 to 70 mmHg and normothermia above 36 degrees C.
- Set up mandatory neuromonitoring and record baselines: SSEPs (posterior columns, median and tibial nerves), MEPs (corticospinal tract, recorded from abductor hallucis, tibialis anterior and abductor digiti minimi), and triggered EMG for pedicle screws (threshold greater than 8 to 10 mA is safe). Re-confirm signals after positioning.
- Position prone on a radiolucent Jackson table. The abdomen must hang free (chest and pelvic supports only) to decompress the IVC and epidural veins, reducing blood loss 30 to 50 percent. Pad every pressure point, especially the eyes (risk of retinal artery occlusion). Arms at 90 degrees abduction or less (more risks brachial plexus stretch); hips flexed 10 to 20 degrees.
- Palpate and mark the spinous processes from two levels above the planned UIV to two levels below the planned LIV.
- Make a single midline posterior incision through skin and subcutaneous tissue (typically 30 to 50 cm depending on curve extent). Cauterise or ligate perforating vessels.
- Identify the thick lumbodorsal (thoracolumbar) fascia overlying the paraspinal muscles and incise it in the midline over the spinous processes.
- Using a Cobb elevator, elevate the erector spinae (spinalis, longissimus, iliocostalis) subperiosteally off the posterior elements. Subperiosteal dissection preserves muscle blood supply and minimises bleeding.
- Expose the spinous processes, laminae, facet joints and transverse processes bilaterally out to the transverse-process tips. The TP tips mark the lateral pedicle anatomy and guide screw placement.
- Dissect laterally to the transverse-process tips but no further. Going lateral to the TP in the thoracic spine risks breaching the pleura.
- Place self-retaining retractors (deep blade on the transverse processes) and achieve meticulous haemostasis: electrocautery for muscle bleeding, bone wax sparingly on cancellous bone (excess wax inhibits fusion).
- Verify levels with intraoperative fluoroscopy before any screw placement. Identify a known landmark (C7, the most prominent cervical spinous process; the ribs, where T12 bears the last rib; or the iliac crest at L4 to L5) and count from there.
- Mark the planned UIV and LIV with a skin marker or needles under fluoroscopy. Confirm on AP and lateral views. The common error is a counting mistake from transitional or lumbosacral anomalies.
- Thoracic pedicles are small (4 to 6 mm at T4 to T8), demanding precise technique.
- Entry point: the intersection of a vertical line along the lateral border of the superior articular facet and a horizontal line bisecting the transverse process (the lateral-superior quadrant of the facet). Decorticate with a burr or awl.
- Gear-shift trajectory: start slightly lateral, then converge 10 to 15 degrees medially in the axial plane, parallel to the superior endplate in the sagittal plane. Aim for 80 percent of vertebral-body width (30 to 35 mm in the mid-thoracic), avoiding anterior cortex perforation.
- Four-wall palpation is mandatory: pass a ball-tip probe and confirm intact medial, lateral, superior and inferior walls. The medial wall is the danger (spinal cord). Confirm with triggered EMG (greater than 8 to 10 mA is safe; less than 5 mA suggests breach). Tap and insert a polyaxial screw (4.5 to 5.5 mm mid-thoracic).
- Lumbar pedicles are larger (8 to 12 mm at L1 to L4, up to 15 mm at L5) and easier to cannulate. Entry point: the junction of the lateral superior-articular-facet border and the superior border of the transverse process (the mamillary region).
- Gear-shift trajectory: start 30 to 45 degrees lateral, then redirect to 10 to 15 degrees medial convergence, creating a J-shaped path that maximises pedicle purchase. Depth 40 to 50 mm (80 percent body width). Avoid bicortical purchase (anterior vessels). The L5 root crosses the L5 pedicle anterolaterally and is most at risk.
- Four-wall palpation and triggered EMG as above. Insert 6.5 to 7.5 mm screws.
- If fusing to the sacrum: S1 entry 1 to 2 mm lateral to the S1 foramen; 25 to 30 degrees medial and caudal toward the promontory; long bicortical screws (60 to 80 mm). S2 alar-iliac screws are an alternative for long lumbosacral constructs.
- After all screws are placed and verified, prepare the fusion bed. Remove facet-joint cartilage completely (a facetectomy with osteotome or burr), since cartilage inhibits fusion.
- Decorticate all posterior elements: roughen the laminae, facets and transverse processes to expose bleeding cancellous bone (pink punctate bleeding signals a viable bed).
- Collect local autograft (spinous-process, laminar and facet bone) in a separate container for grafting later.
- Measure UIV to LIV and select 5.5 mm or 6.35 mm rods (cobalt-chrome is stiffer and holds correction; titanium is less stiff with higher fracture risk if pseudarthrosis develops).
- Rod contouring sets the final sagittal profile and is critical. Contour thoracic kyphosis of 20 to 40 degrees and lumbar lordosis of 40 to 60 degrees (approximating pelvic incidence plus or minus 10 degrees). Use smooth curves only; sharp bends create stress risers.
- Insert the concave rod first (spans a shorter distance, easier to seat), provisionally locking two to three screws at the UIV and LIV. Seat the convex rod second using rod reducers or persuaders with gentle progressive force.
- Correct in all three planes, gradually and incrementally, with continuous neuromonitoring: - Coronal: concave-side compression and convex-side distraction, applied at the apex; limit any single maneuver to less than 50 percent correction. - Axial: rod derotation. With rods provisionally secured, rotate the concave rod posteriorly (about 90 degrees), which translates apical vertebrae toward the midline and improves the rib hump by 30 to 50 percent. - Direct vertebral derotation (DVR) is an adjunct using forceps applied directly to vertebrae under fluoroscopic control.
- Typical correction is 50 to 70 percent of the preoperative Cobb; a residual of 20 to 30 degrees is acceptable. Overcorrection risks neurological injury and coronal imbalance. Sequentially tighten set screws to lock in correction.
- Bone graft is essential (fusion rates of 95 to 98 percent in AIS with modern technique). Local autograft is the gold standard (osteogenic, osteoinductive and osteoconductive); use generously.
- Use allograft (cancellous chips) as an extender and demineralised bone matrix as a supplement when local autograft is insufficient. rhBMP-2 is off-label in the paediatric spine and controversial.
- Mix graft with the patient's blood, pack it firmly into every facet joint bilaterally (the primary fusion mass), and lay it over the decorticated laminae and along the transverse processes. Keep graft out of the canal and foramina.
- Perform final set-screw tightening with a calibrated torque wrench (80 to 120 in-lbs per system), systematically from UIV to LIV.
- Apply cross-links (transverse connectors), typically at the apex of the major curve and at the UIV, to improve torsional rigidity and prevent rod migration.
- Obtain intraoperative radiographs. Confirm screw position, coronal and sagittal alignment, balance of the C7 plumb line over the sacrum, and no hardware prominence. Check that neuromonitoring signals are stable or back to baseline.
- Achieve meticulous haemostasis (electrocautery, bone wax sparingly, topical agents such as Gelfoam-thrombin, Floseal or Surgicel). Irrigate copiously.
- Place two large-bore subfascial closed-suction drains along the fusion, brought out through separate stab incisions lateral to the main wound (not through it). Remove when output is less than 30 to 50 mL per 8-hour shift (typically POD 2 to 4).
- Vancomycin powder (1 to 2 g) is used by some surgeons before closure; evidence is mixed.
- Close in layers. The lumbodorsal fascia closure is critical for wound strength (heavy absorbable suture). Close subcutaneous layers to obliterate dead space, then subcuticular absorbable skin closure with adhesive for the best cosmetic result. Apply a sterile dressing; consider negative-pressure wound therapy for high-risk patients.
The spinal cord lies only 15 to 25 mm anterior to the lamina and is closest to the medial pedicle wall in the mid-thoracic region (T4 to T8). A medial breach can cause devastating cord injury. Prevent it with four-wall palpation of every tract, a triggered-EMG threshold greater than 8 to 10 mA, and continuous MEP/SSEP monitoring. If MEP or SSEP signals alarm, STOP immediately, verify anaesthetic depth and blood pressure (raise MAP to greater than 85 mmHg), remove or reposition the most recently placed screw, and confirm with a wake-up (Stagnara) test if signals do not recover. Prolonged compression beyond about 30 minutes causes irreversible injury.
Modern segmental pedicle-screw fixation achieves three-column correction at every level, giving powerful derotation and translation, whereas historical Harrington distraction was two-point fixation that corrected mainly in the coronal plane and flattened sagittal profile (flat-back). Suk's series established the safety of thoracic pedicle screws: 4604 screws, 1.5 percent malposition and only 0.8 percent screw-related neurological complications.
An abdomen that is not free-hanging, and inadequate tranexamic acid, are the two controllable drivers of blood loss. A less obvious cause of an intraoperative MEP drop is reversible and anaesthetic: hypotension (MAP less than 65 mmHg) or a volatile agent above 1 MAC. Always run the anaesthetic checklist before assuming a cord injury.
Aftercare & Complications
Immediate postoperative care (POD 0 to 1). Admit to ICU or a step-down unit for 24 hours with telemetry and pulse oximetry. Perform hourly neurological checks for the first 24 hours (toe wiggle, dorsiflexion and plantarflexion, light touch); any new deficit demands urgent evaluation and MRI if a hematoma or cord injury is suspected. Use multimodal analgesia (PCA opioid, scheduled acetaminophen, gabapentin or pregabalin, a muscle relaxant, and ketorolac for the first 24 to 48 hours only). Monitor hemoglobin every 6 to 12 hours with a restrictive transfusion threshold (less than 7 to 8 g/dL or symptomatic). Incentive spirometry and early sitting prevent atelectasis. Sequential compression devices start in theatre; chemical prophylaxis is reserved for higher-risk patients. A Foley catheter stays 24 to 48 hours; ileus is common and managed with bowel rest. Inpatient recovery (POD 1 to 5). Mobilise early: sit out on POD 1, ambulate with assistance POD 1 to 2, independent by POD 2 to 3. No brace is required for a stable pedicle-screw construct (a soft corset for comfort is optional). Manage drains by output trend. Obtain standing PA and lateral 36-inch films before discharge. Typical stay is 3 to 5 days once pain is controlled on oral medication, diet is tolerated, the patient ambulates independently, drains are out, and the neuro exam and wound are clean. Outpatient recovery. For the first three months (until fusion solidifies) observe no BLT: no bending at the waist, lifting greater than 5 to 10 lb, or twisting; avoid high-impact activity and encourage walking. Return to school at 3 to 4 weeks. Non-contact sports at 6 months, contact sports at 9 to 12 months after confirmed fusion. Avoid NSAIDs for the first three months (they impair fusion). Keep the incision dry for two weeks; shower after two weeks, no submersion for six weeks. Follow up at 2 weeks (wound check), 6 weeks, 3, 6 and 12 months (the 12-month CT is the gold standard for fusion), then 24 months and annual lifelong checks to watch for late PJK.
- Recognition
- Intraoperative MEP or SSEP change (greater than 50 percent amplitude drop or greater than 10 percent latency increase); postoperative new weakness, sensory deficit, or bowel or bladder dysfunction. Urgent MRI if suspected.
- Prevention
- Continuous MEP/SSEP monitoring, four-wall pedicle palpation, triggered EMG greater than 8 mA, distraction less than 50 percent per maneuver, TIVA without blockade, MAP greater than 65 mmHg.
- Management
- STOP correction, raise MAP to greater than 85 mmHg, remove or reposition the most recent screw, wake-up test to confirm, urgent re-exploration if confirmed; high-dose methylprednisolone is controversial.
- Recognition
- Early (under 6 weeks): erythema, warmth, swelling, drainage, fever, raised inflammatory markers (CRP greater than 100 is strongly suggestive). Late: persistent pain, sinus tract.
- Prevention
- Optimise nutrition (albumin greater than 3.5) and glucose (less than 180), smoking cessation, cefazolin 2 g within 60 min of incision, meticulous haemostasis, normothermia; vancomycin powder is controversial.
- Management
- Superficial: oral antibiotics, irrigation and debridement (I&D) if abscess. Deep: return to theatre for I&D with deep cultures, preserve hardware if early and stable, culture-specific IV antibiotics for 6 weeks; remove hardware only as last resort.
- Recognition
- Months to years postoperatively: proximal back pain, visible kyphosis above the UIV. Defined as greater than 10 degrees kyphosis from UIV to UIV plus 2, and greater than 10 degrees more than preoperative.
- Prevention
- Avoid a UIV at the apex of thoracic kyphosis; choose UIV at the upper end vertebra or stable proximal thoracic (T2 to T4). Avoid over-distraction; restore balanced sagittal alignment. Consider prophylactic hooks, tether or cement in high-risk patients.
- Management
- Asymptomatic and stable: observe with serial radiographs. Symptomatic: conservative trial (PT, NSAIDs, bracing, injections). Progressive, severe, or junctional failure (fracture, neurology): revision with proximal extension of fusion.
- Recognition
- Persistent pain beyond 6 to 12 months, mechanical pain eased by rest. Rod fracture equals pseudarthrosis until proven otherwise; screw halo on X-ray. Flexion-extension motion greater than 3 mm; CT (gold standard) shows no bridging bone.
- Prevention
- Adequate decortication, generous local autograft, rigid fixation, avoid NSAIDs for 3 months, smoking cessation, optimise nutrition (vitamin D greater than 30).
- Management
- Asymptomatic with a stable construct: observe. Symptomatic or rod fracture: revision fusion with thorough decortication, copious graft, larger or dual rods; extend levels or add anterior fusion if recurrent.
- Recognition
- Progressive coronal curve distal to the LIV within the first 2 years: trunk shift, shoulder or waist imbalance, C7 plumb line drifting off the sacrum.
- Prevention
- Select the LIV as the stable or neutral vertebra; include any distal structural curve (corrects less than 25 degrees on bending); watch for disc wedging greater than 3 mm below the planned LIV.
- Management
- Mild (under 10 degrees, balanced): observe. Moderate: trial of observation or bracing if still growing. Severe or progressive (greater than 20 degrees): revision with distal extension to a new stable vertebra.
- Recognition
- Acute pain, loss of correction, palpable prominence, audible pop. X-ray shows broken rod (usually at the apex) or screw. Implant failure usually signals pseudarthrosis.
- Prevention
- Adequate rod diameter (5.5 or 6.35 mm), smooth contour bends, cobalt-chrome for fatigue resistance; achieve solid fusion.
- Management
- With solid fusion on CT and asymptomatic: observe. Symptomatic: hardware removal once fusion confirmed (12 to 24 months). With pseudarthrosis: revision fusion with new hardware.
- Recognition
- POD 3 to 10: nausea, vomiting, early satiety, distension. Upper GI shows a cut-off at the third part of the duodenum; CT angiography shows an SMA-aortic angle less than 25 degrees.
- Prevention
- Maintain perioperative nutrition, avoid over-correction of lumbar lordosis, early mobilisation and upright positioning, high index of suspicion in thin patients (BMI less than 18.5).
- Management
- Conservative (successful in 80 to 90 percent): NPO, NG decompression, IV hydration or TPN, prone or left-lateral positioning, prokinetics, small frequent meals. Surgery (duodenojejunostomy) is rarely needed.
Other early complications include wound dehiscence (local care or reclosure depending on depth), symptomatic hematoma (return to theatre for evacuation), ileus (bowel rest, promotility agents, resolves by POD 3 to 5), and pulmonary complications (atelectasis, pneumonia, PE, managed with incentive spirometry, mobilisation, antibiotics or anticoagulation as appropriate). Other late complications include chronic pain (multimodal management; investigate hardware prominence, adjacent facet arthritis, or nerve injury) and junctional degeneration (adjacent-segment disc and facet wear, treated conservatively first). All show that PJK is the dominant long-term issue and that any rod fracture should be treated as pseudarthrosis until proven otherwise.
Viva & Exam Focus
SAFE PEDICLESAFE PEDICLE — thoracic and lumbar pedicle screw placement
LENKELENKE — classification and fusion-level selection
The cord lies 15 to 25 mm anterior to the lamina, closest in the mid-thoracic region (T4 to T8) where the canal AP diameter is only 12 to 15 mm. Protect with continuous MEP/SSEP monitoring, a 10 to 15 degrees convergent trajectory parallel to the endplate, four-wall palpation, triggered EMG greater than 8 to 10 mA, distraction less than 50 percent per maneuver, and a wake-up test if signals change. A medial breach is catastrophic.
Roots exit the foramina 2 to 5 mm inferior and 3 to 5 mm lateral to the pedicle. The L5 root crosses the L5 pedicle anterolaterally and is most at risk. Protect with a trajectory parallel to the superior endplate (avoid inferior angulation), four-wall palpation, and triggered EMG greater than 8 to 10 mA.
Segmental arteries and veins run along the lateral and anterior body, 10 to 15 mm lateral to the pedicle and 30 to 40 mm anterior to the posterior cortex; the aorta bifurcates at L4. Protect by limiting screws to 80 percent body depth and avoiding lateral breach; bicortical purchase is contraindicated in the thoracic and upper lumbar spine.
The dura lies immediately deep to the ligamentum flavum, only 2 to 5 mm from the lamina (least in the thoracic spine). Protect by using Kerrison rongeurs angled away from the dura, starting laterally and working medially, and palpating frequently. A CSF leak is repaired primarily with 4-0 or 5-0 Nurolon, with fibrin glue or a fascial graft for a large tear.
The parietal pleura lies 10 to 20 mm lateral to the transverse-process tips; the right side is more at risk (the aorta pushes structures rightward). Protect by dissecting subperiosteally only to the TP tips and not beyond, and avoiding aggressive lateral retraction. A recognised tear is repaired primarily if accessible, with a chest tube for a significant pneumothorax; small tears may seal spontaneously.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A 15-year-old girl has a 55-degree right thoracic curve (T5 to T12) and a 38-degree left lumbar curve (L1 to L4). On right bending the thoracic curve corrects to 35 degrees and the lumbar curve to 10 degrees. What is the Lenke classification and what are your fusion levels?”
“During pedicle screw placement at T7 the neuromonitoring team alerts you to a 60 percent drop in MEP amplitudes in the left lower limb immediately after screw insertion, with unchanged SSEPs. What is your immediate management?”
“Two years after PSF T4 to L2 for AIS, a 14-year-old boy's thoracic curve is stable at 27 degrees (from a 60-degree preoperative curve), but you note a new 32-degree kyphosis from T2 to T4 (preoperative 15 degrees). What has happened, what are the risk factors, and how do you manage him?”
Indications
- Cobb angle greater than 45 to 50 degrees (SRS threshold)
- Progression greater than 5 degrees over 6 months despite bracing
- Skeletally mature with curves greater than 40 degrees and unacceptable deformity
- Thoracic curves greater than 50 degrees (adult progression risk)
- Whole-spine MRI mandatory preoperatively in all presumed AIS
Exposure & positioning
- Prone on a Jackson table with the abdomen hanging free (cuts blood loss 30 to 50 percent)
- Midline posterior incision; subperiosteal elevation to the transverse-process tips and no further (pleura)
- Verify levels with fluoroscopy before any screw
- TIVA, no neuromuscular blockade, MAP greater than 65 mmHg, TXA 10 to 15 mg/kg load then 1 mg/kg/hr
Pedicle screws
- Thoracic entry: lateral-superior facet quadrant; lumbar entry: facet to TP junction
- 10 to 15 degrees medial convergence, parallel to the endplate, 80 percent body depth
- Four-wall palpation mandatory; triggered EMG greater than 8 to 10 mA safe
- Polyaxial screws; L5 root most at risk at L5
Correction
- Concave compression plus convex distraction, less than 50 percent per maneuver
- Rod derotation: rotate the concave rod posteriorly to translate the apex and reduce the rib hump
- Continuous neuromonitoring; 50 to 70 percent correction typical, residual 20 to 30 degrees acceptable
- Three-column segmental correction supersedes Harrington distraction
Danger zones
- Spinal cord 15 to 25 mm anterior to lamina; medial breach catastrophic
- Nerve roots 2 to 5 mm inferior to pedicle; L5 root at risk
- Segmental vessels 10 to 15 mm lateral; avoid bicortical thoracic/upper-lumbar
- Dura 2 to 5 mm deep to flavum; angle Kerrisons away
- Pleura 10 to 20 mm lateral to TP tips; dissect only to the tips
Complications
- Neurological injury 0.5 to 1 percent: stop, raise MAP, remove recent screw, wake-up test
- Infection 3 to 5 percent: cefazolin, I&D for deep, preserve hardware if early
- PJK 10 to 30 percent: most common long-term; observe if asymptomatic
- Pseudarthrosis 2 to 5 percent: rod fracture equals pseudarthrosis; revise if symptomatic
- Adding-on 5 to 10 percent: LIV error; prevent by stopping at the stable vertebra
Aftercare
- ICU 24 hours with hourly neuro checks; multimodal analgesia; avoid NSAIDs 3 months
- Mobilise POD 1, no brace needed; drains out when less than 30 to 50 mL per 8 hours
- Discharge POD 3 to 5; no BLT for 3 months
- Non-contact sports 6 months, contact sports 9 to 12 months after confirmed fusion
- CT at 12 to 24 months is the gold standard for fusion; annual lifelong checks for PJK
Exam tips
- Know Lenke cold: type 1 to 6, modifier A/B/C, sagittal minus/N/plus
- Structural curve: greater than 25 degrees and corrects less than 25 degrees on bending
- MEP drop greater than 50 percent: stop, run the checklist, address the recent screw
- PJK definition and that asymptomatic disease is observed
- Rod fracture is pseudarthrosis until proven otherwise
Background & Evidence
Epidemiology and natural history. Adolescent idiopathic scoliosis is the most common form of scoliosis, with a strong genetic component (around 30 percent have an affected family member) and a female predominance, peaking around the adolescent growth spurt. Weinstein's 50-year natural-history study reframes the surgical indication: untreated late-onset idiopathic scoliosis shows no excess mortality versus controls, but curves greater than 80 degrees with a thoracic apex markedly raise the risk of exertional dyspnoea (adjusted OR 9.75), and chronic back pain is more common than in controls (61 versus 35 percent) though usually mild to moderate. Surgery therefore primarily halts progression and improves trunk balance and cosmesis rather than prolonging life, justifying surgery for large thoracic curves and observation or bracing for smaller ones. Pathoanatomy. AIS is a three-dimensional deformity: a coronal curve, altered sagittal profile, and axial rotation of the vertebral bodies toward the convexity (the ribs follow the bodies, producing the posterior rib hump on the convex side). The asymmetry of growth and loading drives progression through the adolescent growth spurt, tracked by the Risser sign of skeletal maturity. The Lenke classification — the system that determines fusion levels. The Lenke system is the global standard for AIS and directly drives which curves are fused. It has three components: a curve type (1 to 6) based on which curves are structural, a lumbar modifier (A/B/C) based on the position of the lumbar apex relative to the centre sacral vertical line (CSVL), and a sagittal modifier (minus/N/plus) based on the T5 to T12 kyphosis. A curve is structural when its Cobb angle is greater than 25 degrees and it corrects by less than 25 degrees on side-bending films.
- Definition
- Only the main thoracic curve is structural
- Surgical implication
- Fuse the thoracic curve only
- Definition
- Proximal and main thoracic curves both structural
- Surgical implication
- Fuse both thoracic curves
- Definition
- Main thoracic and thoracolumbar or lumbar both structural
- Surgical implication
- Fuse thoracic and lumbar
- Definition
- Proximal thoracic, main thoracic and TL/L all structural
- Surgical implication
- Fuse all three curves
- Definition
- Only the thoracolumbar or lumbar curve is structural
- Surgical implication
- Fuse the lumbar curve only
- Definition
- TL/L is the primary curve, main thoracic also structural
- Surgical implication
- Fuse both
- Definition
- Apex between the pedicles, does not cross the CSVL
- Surgical implication
- Lumbar fusion usually not needed
- Definition
- Apex touches the CSVL or sits just medial to it
- Surgical implication
- Consider lumbar extension
- Definition
- Apex crosses the CSVL medially
- Surgical implication
- Lumbar extension typically required
- Definition
- T5 to T12 kyphosis under 10 degrees
- Surgical implication
- Restore kyphosis during correction
- Definition
- T5 to T12 kyphosis 10 to 40 degrees
- Surgical implication
- Maintain kyphosis
- Definition
- T5 to T12 kyphosis over 40 degrees
- Surgical implication
- Limit derotation to preserve kyphosis
Key evidence. The modern operation rests on three pillars: the Lenke classification for level selection (Lenke 2001), the safety and power of thoracic pedicle screws (Suk 2001), and the recognition that PJK is the dominant long-term complication (Kim 2005). Blood conservation with tranexamic acid is now Level I supported (Verma 2014), and neuromonitoring cut the permanent neurological injury rate from around 1 percent to 0.1 percent (Nuwer 1995). Full citations and findings are in References.
References
Adolescent idiopathic scoliosis: a new classification to determine extent of spinal arthrodesis (Lenke classification)
- Three-component system: curve type 1 to 6, lumbar modifier (A/B/C) based on the apex-to-CSVL relationship, and sagittal thoracic modifier (minus/N/plus) based on the T5 to T12 Cobb angle.
- Interobserver and intraobserver kappa were 0.74 to 0.89 for curve type, 0.80 to 0.84 for lumbar modifier, and 0.94 to 0.97 for sagittal modifier (good to excellent reliability).
- Substantially more reliable than the older King classification and directly guides which curves are structural and must be fused.
Thoracic pedicle screw fixation in spinal deformities: are they really safe?
- 462 patients, 4604 thoracic pedicle screws: malposition rate 1.5 percent (67 screws), of which only 4 were medial; screw-related neurological complications in 0.8 percent (one transient paraparesis, three dural tears).
- Mean coronal correction 69.9 percent for idiopathic and 60.7 percent for congenital scoliosis, with no permanent screw-related neurological or visceral injury.
- Established that thoracic pedicle screws achieve superior three-column correction with a high margin of safety when placed with sound technique.
Proximal junctional kyphosis in AIS following segmental posterior spinal instrumentation and fusion: minimum 5-year follow-up
- 193 AIS patients, mean 7.3-year follow-up: PJK incidence 26 percent, defined as proximal junctional sagittal Cobb (UIV lower endplate to two supra-adjacent vertebrae) over 10 degrees and at least 10 degrees greater than preoperative.
- Most progression occurred within the first 2 years (mean 15.2 degrees) then stabilised; significant risk factors were thoracoplasty, hybrid (proximal hook, distal screw) constructs, and preoperative T5 to T12 kyphosis over 40 degrees.
- SRS-24 outcome scores did not differ between PJK and non-PJK groups.
The relative efficacy of antifibrinolytics in adolescent idiopathic scoliosis: a prospective randomized trial
- Double-blind RCT of 125 AIS patients randomised to tranexamic acid, epsilon-aminocaproic acid, or saline placebo during posterior arthrodesis.
- Both antifibrinolytics reduced estimated blood loss and the postoperative haematocrit drop; tranexamic acid additionally reduced drain output and total blood loss versus placebo and aminocaproic acid.
- No difference in transfusion rate, operative time, levels fused or screws placed between groups.
Health and function of patients with untreated idiopathic scoliosis: a 50-year natural history study
- Prospective 50-year follow-up of 117 untreated late-onset idiopathic scoliosis patients versus 62 matched controls: survival approximately 0.55 versus 0.57 expected, i.e. no excess mortality.
- Curves over 80 degrees with a thoracic apex carried a markedly increased risk of exertional dyspnoea (adjusted OR 9.75); chronic back pain was more common than controls (61 versus 35 percent) but usually mild to moderate.
- Untreated adults remained productive and functional, refuting the belief that all idiopathic scoliosis inevitably ends in disability.
Non-neurologic complications following surgery for adolescent idiopathic scoliosis
Prospective multicentre cohort of 702 AIS patients: overall non-neurologic complication prevalence 15.4 percent (respiratory 1.4 percent, wound infection 0.7 percent). Increased operative blood loss, prolonged posterior surgery or anaesthesia time, and renal disease were the main risk factors, supporting blood conservation and operative-efficiency strategies.
Somatosensory evoked potential spinal cord monitoring reduces neurologic deficits after scoliosis surgery
Landmark multicentre survey demonstrating that SSEP spinal cord monitoring reduces permanent neurological injury from around 1 percent to 0.1 percent in scoliosis surgery, establishing neuromonitoring and its alarm criteria (greater than 50 percent amplitude drop or greater than 10 percent latency increase) as the standard of care.
The Spinal Appearance Questionnaire: reliability, validity and responsiveness in idiopathic scoliosis
Validated a patient-reported instrument for perceived spinal deformity appearance that is reliable, valid and responsive to surgical curve correction, underscoring that cosmesis and self-image are central, measurable outcomes of AIS surgery and key to informed-consent counselling in adolescents.
The posterior approach for lumbar and thoracolumbar AIS: posterior shortening and pedicle screws
Prospective series of 62 thoracolumbar or lumbar AIS curves treated with wide posterior release and segmental pedicle screws (613 screws placed safely): 80 percent coronal correction (52 to 10 degrees), normalised lumbar lordosis and restored coronal balance, with no pseudarthrosis, infection or reoperation, establishing the posterior-only pedicle-screw approach as a preferred technique.
Long-term functional and radiologic outcomes after Harrington instrumentation for AIS
Long-term (mean 20.8-year) outcomes after Harrington instrumentation for AIS in 78 patients: clinical outcome did not correlate with radiographic correction, trunk strength matched the normal population and patients functioned well, though side-bending mobility was reduced in 59 percent, establishing that AIS surgery has durable functional benefit despite loss of spinal motion and that cosmesis correlates with residual curve magnitude.