Spinal Osteotomy Techniques: PSO, VCR, and SPO

High Yield Overview

SPINAL OSTEOTOMY TECHNIQUES

PSO, VCR, and SPO for Deformity Correction

10degSPO correction per level

30-40degPSO correction per level

50-70degVCR correction per level

Schwab Classification

Grade 1-2

PatternSPO - posterior column only

TreatmentFlexible deformity, 10deg/level

Grade 3

PatternPSO - all three columns

TreatmentRigid flatback, 30-40deg/level

Grade 4-6

PatternVCR - complete vertebrectomy

TreatmentSevere rigid deformity, 50-70deg

Critical Must-Knows

SPO: Posterior column only, requires intact anterior column as hinge, low neuro risk (1-3%)
PSO: All three columns via posterior approach, L3 optimal level, moderate neuro risk (5-11%)
VCR: Complete vertebrectomy, highest correction but highest risk (10-25% neurological)

Examiner's Pearls

"
Match osteotomy to deformity: SVA less than 100mm flexible = SPOs; SVA greater than 100mm rigid = PSO; SVA greater than 150mm angular = VCR
"
Neuromonitoring mandatory (SSEP + MEP); maintain MAP greater than 85 during closure
"
L3 is optimal PSO level - below conus medullaris, cauda equina tolerates manipulation

High Yield Exam Topic

PSO and VCR are high-risk procedures requiring experienced surgical teams, neuromonitoring, ICU capability, and appropriate patient selection. Examiners assess: (1) Biomechanical principles - which osteotomy for which deformity, (2) Technical mastery of each procedure, (3) Ability to prevent and manage neurological complications. Know the Schwab classification grades, correction potential per level, and response to neuromonitoring changes.

At a Glance

Spinal osteotomies enable powerful deformity correction with increasing complexity and risk. SPO (Smith-Petersen osteotomy) is a posterior column only procedure providing 10 degrees per level through a posterior-opening wedge with intact anterior column as hinge. PSO (pedicle subtraction osteotomy) resects all three columns via posterior approach, achieving 30-40 degrees correction at a single level with 10-15mm shortening. VCR (vertebral column resection) removes the entire vertebra allowing 50-70 degrees correction but carries highest risk. Neurological complication rates increase with complexity: SPO 1-3%, PSO 5-11%, VCR 10-25%. Match osteotomy type to deformity magnitude - neuromonitoring is mandatory.

Mnemonic

OSTEOTOMYOSTEOTOMY Patient Selection Criteria

O - Objectives clear (restore sagittal balance, improve function)

S - Sagittal imbalance severe (SVA greater than 50mm, PI-LL greater than 20)

T - Trial of conservative management failed (minimum 6 months)

E - Expectations realistic (60-70% improvement, not cure)

O - Osteoporosis optimized (DEXA, vitamin D, teriparatide if needed)

T - Type of osteotomy matches deformity (SPO vs PSO vs VCR)

O - Other comorbidities controlled (cardiac, diabetes, nutrition)

M - Medical fitness confirmed (cardiac, pulmonary clearance)

Y - Young enough for recovery (age less than 75 preferred)

Memory Hook:Examiners expect you to demonstrate judgment in patient selection. Osteotomy in wrong patient leads to disaster.

Anatomy & Pathophysiology

Three-Column Concept of the Spine

Denis Three-Column Model:

Anterior Column:
- Anterior longitudinal ligament
- Anterior half of vertebral body
- Anterior half of disc
Middle Column:
- Posterior half of vertebral body
- Posterior half of disc
- Posterior longitudinal ligament
Posterior Column:
- Pedicles, laminae, facets
- Ligamentum flavum
- Interspinous and supraspinous ligaments

Osteotomy Classification by Columns Affected:

SPO: Posterior column only (Grade 1-2 osteotomy)
PSO: All three columns (Grade 3 osteotomy)
VCR: All three columns with complete vertebral resection (Grade 4-6 osteotomy)

Biomechanical Principles

Axis of Rotation:

SPO: Axis anterior to anterior longitudinal ligament
- Opens posteriorly, closes anteriorly
- Requires intact anterior column to act as hinge
- Limited correction potential per level
PSO: Axis through middle of vertebral body
- Symmetrical closure
- No anterior column hinge required
- Greater correction potential per level
VCR: Axis at surgeon's choice (depends on rod position)
- Maximum flexibility in correction plane
- Can address both sagittal and coronal deformity simultaneously
- Requires temporary instability during closure

Correction Potential:

SPO: 10 degrees per level (range 5-15 degrees)
PSO: 30-40 degrees per level (range 25-45 degrees)
VCR: 50-70 degrees per level (range 40-80 degrees)

Spinal Shortening:

SPO: Minimal shortening (anterior column intact)
PSO: 10-15mm shortening at osteotomy level
VCR: 20-40mm shortening (entire vertebra removed)
Shortening relaxes neural elements but may affect visceral structures

Anatomical Considerations

Vascular Anatomy:

Lumbar Segmental Arteries: Exit at mid-vertebral body
- At risk during PSO (vertebral body resection)
- Sacrifice usually tolerated due to collaterals
- Excessive bleeding risk in vascular disease
Artery of Adamkiewicz:
- Typically T9-L2 on left (75% of cases)
- Major anterior spinal artery supply
- Injury causes paraplegia (anterior cord syndrome)
- Risk minimized by maintaining MAP greater than 85 mmHg

Neural Anatomy:

Conus Medullaris: Typically T12-L2
- Higher risk of myelopathy if osteotomy at this level
- Lumbar levels (L3-L4) preferred for PSO
Cauda Equina: Below L2
- More tolerant of manipulation than spinal cord
- Individual nerve roots can be mobilized
Exiting vs Traversing Roots:
- Exiting root in neural foramen (vulnerable to pedicle work)
- Traversing root medial to pedicle (vulnerable to canal work)

Classification

Schwab Classification of Spinal Osteotomies

Schwab Classification of Osteotomy Grades

category	structuresResected	columnsAffected	correctionPotential	axisOfRotation	examples	risk
Grade 1 - Partial Facetectomy	Inferior facet only	Posterior (partial)	Less than 10 degrees per level	Anterior to ALL	Multiple level releases for mild kyphosis	Very low
Grade 2 - SPO (Smith-Petersen)	Facets, ligamentum flavum, spinous process	Posterior (complete)	10 degrees per level	Anterior to ALL	Ankylosing spondylitis, mild fixed kyphosis	Low (1-3% neuro)
Grade 3 - PSO (Pedicle Subtraction)	Posterior elements, pedicles, posterior VB wedge	All three columns	30-40 degrees per level	Middle of VB	Flatback deformity, severe sagittal imbalance	Moderate (5-11% neuro)
Grade 4 - VCR Posterior Only	Entire vertebra from posterior approach	All three columns (complete)	50-60 degrees	Surgeon-controlled	Severe rigid kyphosis, angular deformity	High (10-15% neuro)
Grade 5 - VCR Staged Posterior-Anterior	Complete vertebrectomy via two approaches	All three columns with wide exposure	60-70 degrees	Surgeon-controlled	Severe rigid deformity with anterior pathology	Very high (15-20% neuro)
Grade 6 - VCR with Bone Resection	Multiple vertebrae or asymmetric resection	Extended multi-level all columns	Greater than 70 degrees	Multiple axes	Severe congenital deformity, tumor resection	Very high (20-25% neuro)

Anatomic Location Classification

Cervical Osteotomies:

Highest neurological risk (spinal cord injury = quadriplegia)
Typically SPO or opening wedge osteotomy
PSO/VCR rarely performed (extreme risk)

Thoracic Osteotomies:

T1-T10: Spinal cord present, myelopathy risk
Narrow canal, less room for error
PSO preferred over VCR when possible

Thoracolumbar Osteotomies:

T11-L2: Conus medullaris level (high risk)
Avoid if possible, prefer L3-L4 for PSO

Lumbar Osteotomies:

L3-L4: Preferred level for PSO (below conus, cauda equina tolerates manipulation)
L5: Avoid PSO (proximity to sacrum, large vessels)

Sacral Osteotomies:

Rare, typically for pelvic incidence reduction
S1 or S2 level
Risk of bowel/bladder dysfunction

Deformity-Based Classification

Sagittal Plane Deformities:

Flatback: PSO for lordosis restoration
Kyphosis: PSO or VCR depending on magnitude and rigidity
Chin-on-chest: Multiple SPOs or cervicothoracic VCR

Coronal Plane Deformities:

Scoliosis: Asymmetric VCR for coronal and rotational correction
Coronal Imbalance: VCR at apex with lateral translation

Combined Deformities:

Kyphoscoliosis: VCR for simultaneous sagittal and coronal correction
3D Deformity: Multiple osteotomies or extended VCR

Clinical Presentation

Patient Selection for Osteotomy

Ideal Candidate for PSO:

Fixed sagittal imbalance (SVA greater than 50mm, PI-LL mismatch greater than 20 degrees)
Failed conservative management (minimum 6 months)
Rigid deformity not correctable with positioning
Good bone quality (T-score greater than -2.0)
Age less than 70 years
Medical fitness for major surgery
Realistic expectations

Contraindications to Osteotomy:

Absolute:

Active infection at osteotomy site
Severe osteoporosis (T-score less than -3.5) without treatment
Prohibitive medical comorbidities (severe cardiac, pulmonary disease)
Unrealistic expectations or psychiatric contraindications

Relative:

Age greater than 75 years
Moderate osteoporosis (T-score -2.5 to -3.0)
Prior radiation to osteotomy site
Severe obesity (BMI greater than 40)
Revision at same level

Deformity Assessment

Radiographic Assessment:

Standing Full-Length Spine: AP and lateral
Sagittal Parameters:
- SVA: Normal less than 50mm
- PI-LL mismatch: Normal within 10 degrees
- Pelvic tilt: Compensation mechanism (normal less than 20 degrees)
- Thoracic kyphosis: Normal 20-50 degrees

Deformity Magnitude:

Mild: SVA 50-75mm, PI-LL 10-20 degrees → Multiple SPOs
Moderate: SVA 75-150mm, PI-LL 20-40 degrees → Single PSO
Severe: SVA greater than 150mm, PI-LL greater than 40 degrees → PSO + SPOs or VCR

Flexibility Assessment:

Supine Hyperextension Film: Assesses deformity flexibility
Traction Films: Pull test for deformity reducibility
Rigid Deformity: Less than 10 degree correction on flexibility films → PSO or VCR
Flexible Deformity: Greater than 20 degree correction → SPOs may suffice

Preoperative Evaluation

Medical Clearance:

Cardiac evaluation (ECG, echo if indicated, stress test if CAD risk)
Pulmonary function tests if restrictive lung disease
Renal function (creatinine clearance for contrast studies, blood loss)
Coagulation studies and type/screen (anticipate 2-4 unit PRBC transfusion)

Neurological Baseline:

Document complete neurological examination
MRI to assess spinal cord (myelomalacia, stenosis, tumor)
Consider urodynamics if bowel/bladder symptoms

Bone Quality:

DEXA scan mandatory
Optimize if osteoporotic (vitamin D, calcium, teriparatide)
Consider cement augmentation if T-score less than -2.5

Management Algorithm

Osteotomy Selection Algorithm:

Assess Deformity Magnitude:
- SVA less than 100mm with flexible deformity: Multiple SPOs
- SVA 100-150mm with rigid deformity: Single PSO at L3
- SVA greater than 150mm or severe angular deformity: PSO + SPOs or VCR
Evaluate Rigidity:
- Greater than 20 degrees correction on flexibility films: SPOs may suffice
- Less than 10 degrees correction: Requires bony osteotomy (PSO or VCR)
Match Correction to Deformity:
- SPO: 10 degrees per level (posterior column only)
- PSO: 30-40 degrees per level (all three columns)
- VCR: 50-70 degrees per level (complete vertebrectomy)

Surgical Techniques

Smith-Petersen Osteotomy (SPO)

Indications:

Flexible kyphosis requiring 10-30 degrees total correction
Ankylosing spondylitis with mild-moderate deformity
Scheuermann's kyphosis
Post-laminectomy kyphosis (iatrogenic flatback)

Technique:

Step 1 - Exposure:

Midline incision over planned osteotomy levels
Subperiosteal dissection exposing laminae and facets
Identify levels with radiograph (count from C7 or sacrum)

Step 2 - Posterior Element Resection:

Remove inferior facet completely (leave superior facet intact)
Remove ligamentum flavum
Resect spinous process and interspinous ligament
Thin superior lamina to create hinge point
Wide resection creates V-shaped gap

Step 3 - Instrumentation:

Place pedicle screws 2-3 levels above and below each osteotomy
Temporary rods to maintain stability during multiple osteotomies

Step 4 - Closure:

Gradual compression on rods closes posterior gap
Anterior column acts as hinge (must be intact)
Monitor neuromonitoring during closure
Achieve desired lordosis restoration

Step 5 - Final Fixation:

Permanent rod placement
Cross-links for rotational stability
Bone graft over osteotomy sites

Pearls:

Multiple levels better than single level (distributes stress)
Apex of kyphosis is optimal location
Preserve anterior column (DO NOT violate anterior longitudinal ligament)
Gradual closure reduces neurological risk

Pitfalls:

Fracture through anterior column (loss of hinge, unstable)
Excessive correction at single level (neurological injury)
Inadequate facet resection (limited correction, rod stress)

Pedicle Subtraction Osteotomy (PSO)

Indications:

Fixed sagittal imbalance requiring 30-40 degrees correction
Flatback deformity with PI-LL mismatch greater than 20 degrees
Rigid kyphosis not amenable to SPO
Revision deformity surgery

Optimal Level Selection:

L3: Most common (below conus, good bone stock, central lordosis)
L2: Acceptable if L3 anatomy unfavorable
L4: Avoid if possible (proximity to L5-S1, lordosis distribution)
Thoracic: High risk (spinal cord), avoid if possible

Technique:

Step 1 - Exposure and Instrumentation:

Wide midline exposure from 3-4 levels above to 3-4 levels below
Place all pedicle screws first (including osteotomy level)
Temporary rods for stability
Identify osteotomy level with fluoroscopy

Step 2 - Posterior Element Resection:

Complete laminectomy at osteotomy level (L3)
Bilateral facetectomy (L2-L3 and L3-L4)
Resect spinous processes L2, L3, L4
Expose pedicles completely (circumferential)
Identify and protect nerve roots (exiting L3 root at risk)

Step 3 - Pedicle Resection:

Remove pedicles with osteotomes or high-speed burr
Start lateral, work medial to avoid nerve injury
Create cortical shell of posterior vertebral body
Expose lateral walls of vertebral body

Step 4 - Vertebral Body Resection:

Use curettes, osteotomes, or high-speed burr
Create wedge-shaped defect (wider posteriorly)
Preserve anterior cortex (1-2mm shell)
Angle: 30-40 degrees from horizontal
Copious irrigation to prevent thermal injury

Step 5 - Temporary Stabilization:

Place temporary rods with moderate compression
Prevents premature closure during contralateral work
Maintain canal decompression

Step 6 - Closure:

Gradually compress bilateral rods
Posterior wedge closes, anterior cortex fractures (controlled hinge)
Monitor neuromonitoring (SSEP, MEP) continuously
Stop if significant neuromonitoring changes
Shortening of 10-15mm relaxes neural elements

Step 7 - Final Fixation:

Permanent rod placement (cobalt-chromium 6.0-6.35mm)
Dual rods for high-stress cases
Multiple cross-links (every 3-4 levels)
Bone graft entire construct

Intraoperative Pearls:

Four-Rod Technique: Temporary rods during osteotomy, permanent rods after closure
Cell Saver: Autotransfusion reduces allogeneic blood transfusion
Hypotensive Anesthesia: Reduce blood loss (maintain MAP 65-70 during resection)
Maintain MAP greater than 85 during closure: Spinal cord perfusion
Have wake-up test ready: If neuromonitoring changes persist

Complications During PSO:

Excessive Bleeding: Segmental arteries, epidural plexus
- Management: Hemostatic agents, temporary closure, blood transfusion
Neurological Injury: Traction on nerve roots, cord ischemia
- Management: Release compression, augment blood pressure, consider wake-up test
Anterior Cortex Fracture Too Early: Uncontrolled closure
- Management: Temporary stabilization, controlled gradual closure
Inadequate Correction: Insufficient bone resection
- Management: Remove more bone (carefully), accept and add SPO at adjacent level

Vertebral Column Resection (VCR)

Indications:

Severe rigid deformity requiring greater than 50 degrees correction
Sharp angular kyphosis (kyphoscoliosis)
Congenital deformity (hemivertebra, bar)
Tumor resection with reconstruction
Failed PSO requiring salvage

Level Selection:

Apex of deformity (maximum correction with single level)
Avoid conus medullaris (T12-L2) if possible
Thoracic VCR requires ICU monitoring (cord injury = paraplegia)

Technique:

Step 1 - Extensive Exposure:

Wide exposure 5-6 levels above and below
Circumferential exposure of vertebra to be resected
Place all pedicle screws excluding VCR level

Step 2 - Posterior Element Removal:

Complete laminectomy at VCR level and adjacent levels
Bilateral facetectomies above and below
Identify and protect nerve roots (dura completely exposed)

Step 3 - Pedicle and Posterior VB Resection:

Resect pedicles bilaterally with burr or osteotome
Remove posterior wall of vertebral body
Create working channel to anterior column

Step 4 - Lateral and Anterior VB Resection:

Blunt dissection laterally (protect great vessels)
Ligate segmental arteries if necessary
Resect vertebral body completely (anterior cortex last)
Elevate disc above and below (remove completely)

Step 5 - Temporary Stabilization:

Place temporary rods to prevent catastrophic collapse
Dura completely exposed (360 degree decompression)
Sac of neural elements free-floating

Step 6 - Gradual Closure and Correction:

Slowly compress rods to close gap
Monitor neuromonitoring continuously
Translate spine as needed for coronal correction
Rotate spine for rotational correction
Shortening of 20-40mm

Step 7 - Anterior Column Reconstruction:

Place structural graft (cage, mesh, allograft bone)
Provides anterior column support
Allows bone ingrowth for fusion
Prevents kyphosis recurrence

Step 8 - Final Fixation:

Robust fixation with dual rods (four-rod construct)
Cobalt-chromium 6.35mm diameter
Multiple cross-links for stability
Extend fixation 4-5 levels beyond VCR

Anterior vs Posterior-Only VCR:

Posterior-Only (Single-Stage):

Advantages: Single surgery, less morbidity, shorter recovery
Disadvantages: Limited anterior access, higher blood loss, more technically demanding
Preferred for most cases if surgeon experienced

Staged Anterior-Posterior:

Advantages: Better anterior column visualization, controlled resection
Disadvantages: Two surgeries, increased morbidity, longer hospitalization
Indicated for: Tumor resection, extensive anterior pathology, vascular anomalies

Complications of VCR:

Neurological Injury (10-25%): Highest of all osteotomies
- Prevention: Meticulous technique, neuromonitoring, gradual closure
Vascular Injury: Great vessels, segmental arteries
- Prevention: Blunt dissection, vascular surgery standby for thoracic VCR
Massive Blood Loss: Average 2-5 liters
- Prevention: Cell saver, controlled hypotension, hemostatic agents
Construct Failure: Rod fracture, screw pullout
- Prevention: Robust fixation (dual rods, extend fixation)

Mnemonic

TECHNIQUEPSO Stepwise TECHNIQUE

T - Temporary rods placed after instrumentation

E - Expose and remove posterior elements (laminectomy, facetectomy)

C - Cut pedicles carefully (preserve nerve roots)

H - Hollow out vertebral body (wedge 30-40 degrees)

N - Neuromonitoring active (SSEP, MEP) throughout

I - Instrument with permanent rods (gradual compression)

Q - Quality check (fluoroscopy confirms closure)

U - Utilize cross-links (rotational stability)

E - Elevate blood pressure (MAP greater than 85) during closure

Memory Hook:Examiners assess technical knowledge. Demonstrate you understand every step and rationale. Emphasize neuromonitoring and gradual closure for safety.

Postoperative Management

Immediate Postoperative Care (ICU - First 24-48 Hours)

Neurological Monitoring:

Frequent Neuro Checks: Every 1-2 hours for first 24 hours
Document: Motor strength (all myotomes), sensation, reflexes
Wake Patient Early: Assess for deficits as soon as safely extubated
Urgent MRI if Deficit: Rule out hematoma, hardware malposition

Hemodynamic Management:

Maintain MAP greater than 85 mmHg: Spinal cord perfusion (first 48 hours)
Vasopressors if Needed: Phenylephrine or norepinephrine
Fluid Resuscitation: Replace blood loss (target Hb greater than 8 g/dL)
Monitor Urine Output: Target greater than 0.5 mL/kg/hour

Pain Management:

Multimodal Analgesia: Acetaminophen, NSAIDs (if renal function allows), gabapentin
Epidural: Excellent pain control if placed preoperatively
PCA (Patient-Controlled Analgesia): Opioids as needed
Avoid Excessive Opioids: Delirium, ileus, respiratory depression

Drain Management:

Closed Suction Drains: Monitor output (expect 200-400 mL first 24 hours)
Remove When Output less than 50 mL per 8 hours: Typically POD 2-3
Watch for Excessive Bleeding: Greater than 500 mL in 8 hours → consider re-exploration

Early Mobilization (POD 1-5)

Out of Bed:

POD 1: Sit at edge of bed if neurologically intact
POD 2: Sit in chair, stand with assistance
POD 3: Walk with walker or assistance
Goal: Walking independently by discharge

Bracing:

TLSO Brace: For PSO/VCR patients, worn for 12 weeks
No Brace if SPO Only: Unless multiple levels or poor bone quality
Custom-Molded: Better fit, compliance

Physical Therapy:

Early Mobilization: Reduces DVT, pneumonia, ileus
Core Strengthening: Gentle isometrics (no trunk rotation for 12 weeks)
Gait Training: Restore normal gait pattern
ADL Training: Transfers, stairs, dressing

Complications and Management

Neurological Deficit:

Immediate Postoperative Deficit:

Urgency: Emergent evaluation
Differential: Epidural hematoma (most common), hardware malposition, cord ischemia
Workup: Urgent MRI, check coagulation studies
Management:
- Hematoma: Emergent evacuation (decompress within 8 hours for best recovery)
- Hardware malposition: Revision to remove offending screw/rod
- Cord ischemia: Augment MAP to 90-100 mmHg, steroids controversial (no proven benefit)

Delayed Deficit (POD 1-7):

Causes: Delayed hematoma, overcorrection with stretch injury, cord ischemia
Management: Similar to immediate deficit, MRI to differentiate

Neurological Recovery:

Incomplete Deficits: 50-70% significant recovery
Complete Deficits: Poor prognosis (less than 20% recovery)
Nerve Root Injuries: Better prognosis than cord injuries

Wound Complications:

Hematoma/Seroma: Aspiration vs surgical drainage
Superficial Infection: Antibiotics, local wound care
Deep Infection: Irrigation and debridement, retain hardware if early (less than 3 months)

Medical Complications:

DVT/PE: Mechanical prophylaxis POD 0, chemical POD 1 (after drain removal)
Ileus: Early mobilization, minimize opioids, NG tube if severe
Pneumonia: Incentive spirometry, early mobilization, respiratory therapy
Delirium: Especially age greater than 65, minimize opioids and benzos, reorient

Surveillance and Follow-Up

Early Follow-Up (First 3 Months):

2 Weeks: Wound check, staple removal, neurological exam
6 Weeks: Radiographs (AP/Lateral standing), advance PT, pain assessment
12 Weeks: Radiographs, discontinue brace if appropriate, functional assessment

Late Follow-Up (3 Months to 2 Years):

6 Months: Radiographs, CT if fusion concern, return to light activities
12 Months: Radiographs and CT to confirm fusion, return to full activities
24 Months: Final radiographs, assess for adjacent segment degeneration

Radiographic Assessment:

Immediate Postop: Confirm correction achieved, hardware position
6 Weeks: Assess for early hardware failure (screw loosening, rod fracture)
12 Weeks: Look for loss of correction
12 Months: CT to confirm fusion (greater than 50% bridging bone)

Functional Outcome Measures:

ODI (Oswestry Disability Index): Baseline, 6 months, 12 months
SRS-22: Spine-specific quality of life
VAS Pain Score: Track pain improvement
Walking Distance: Objective functional measure

Complications

Neurological Complications

Neurological Complications by Osteotomy Type

category	overallIncidence	motorDeficit	sensoryDeficit	mechanisms	prevention	recovery
Smith-Petersen Osteotomy	1-3%	0.5-1%	1-2%	Nerve root traction from excessive correction at single level	Multiple levels, gradual correction, preserve anterior column	70-80% significant recovery
Pedicle Subtraction Osteotomy	5-11%	3-6%	4-8%	Root injury during pedicle resection, cord ischemia from correction, epidural hematoma	Neuromonitoring, gradual closure, maintain MAP greater than 85, meticulous hemostasis	50-60% significant recovery
Vertebral Column Resection	10-25%	8-15%	10-18%	Cord manipulation, vascular injury (artery of Adamkiewicz), excessive shortening, translation	Experienced team, ICU monitoring, gradual closure, limit shortening to 30mm	40-50% significant recovery

Risk Factors for Neurological Injury:

Revision osteotomy at same level (epidural scarring)
Thoracic location (spinal cord present)
Excessive correction (greater than 40 degrees PSO, greater than 60 degrees VCR)
Osteoporosis (vertebral body fracture during closure)
Vascular disease (cord ischemia)

Neuromonitoring:

SSEPs (Somatosensory Evoked Potentials): Monitor dorsal column
- Alert: Greater than 50% amplitude decrease or greater than 10% latency increase
- Sensitivity: 75-85% for sensory deficits
MEPs (Motor Evoked Potentials): Monitor corticospinal tract
- Alert: Greater than 50% amplitude decrease
- Sensitivity: 85-95% for motor deficits (more reliable than SSEPs)
Triggered EMG: Pedicle screw placement, nerve root monitoring
Continuous Free-Running EMG: Nerve root irritation during dissection

Response to Neuromonitoring Changes:

Notify surgeon immediately
Augment blood pressure (MAP to 90-100 mmHg)
Release recent manipulation (stop compression, reduce correction)
Reassess signals (wait 10-15 minutes)
Wake-up test if signals do not return
Accept less correction if needed (neurological preservation paramount)

Vascular Complications

Major Vascular Injury (Rare, Less than 1%):

Great Vessels: Aorta, IVC (during anterior VCR exposure)
Iliac Vessels: L4-L5 PSO or VCR
Segmental Arteries: Ligated during PSO/VCR (usually tolerated)

Prevention:

Blunt dissection laterally (protect vessels)
Vascular surgery standby for high-risk cases
Avoid anterior cortex violation until final closure

Management:

Immediate vascular surgery consultation
Direct pressure, hemostatic agents
Repair or graft if major vessel injured
Massive transfusion protocol

Artery of Adamkiewicz Injury:

Anterior spinal artery thrombosis → paraplegia
Prevention: Maintain MAP greater than 85, avoid excessive hypotension
No effective treatment once injury occurs (devastating complication)

Mechanical Complications

Rod Fracture:

Incidence: 5-10% at 2 years (higher with PSO/VCR)
Risk Factors: Single rods, small diameter (5.5mm), pseudarthrosis
Prevention: Dual rods, 6.35mm diameter, achieve solid fusion
Management: Revision if symptomatic or pseudarthrosis present

Screw Loosening/Pullout:

Incidence: 3-5% (higher in osteoporosis)
Risk Factors: Osteoporosis, inadequate screw purchase, excessive stress
Prevention: Cement augmentation if T-score less than -2.5, bicortical screws
Management: Revision with longer/larger screws or cement augmentation

Proximal Junctional Kyphosis (PJK):

Incidence: 20-40% after PSO/VCR
Risk Factors: Osteoporosis, overcorrection, UIV at inflection point
Prevention: Prophylactic vertebroplasty at UIV, gradual lordosis transition
Management: Observation if asymptomatic, revision if symptomatic/severe

Pseudarthrosis:

Incidence: 10-20% at 2 years
Risk Factors: Smoking, diabetes, osteoporosis, inadequate biologics
Prevention: Smoking cessation, autograft + BMP, teriparatide
Management: Revision if symptomatic or hardware failure

Mnemonic

MONITORMONITOR During Osteotomy Closure

M - Maintain MAP greater than 85 mmHg (spinal cord perfusion)

O - Observe neuromonitoring continuously (SSEP, MEP)

N - Notify surgeon of ANY signal changes immediately

I - Incremental closure (gradual compression, not sudden)

T - Test wake-up if signals lost (confirm motor function)

O - Optimize blood pressure if neuro changes (MAP 90-100)

R - Release correction if signals do not recover (safety first)

Memory Hook:Examiners expect detailed understanding of intraoperative neuromonitoring. Explain what each modality monitors and how you respond to changes.

Prognosis and Outcomes

Expected Outcomes by Osteotomy Type

Smith-Petersen Osteotomy:

Correction Achieved: 90-95% achieve planned correction (10 degrees per level)
Pain Relief: 70-80% significant improvement
Fusion Rate: 90-95% (low-stress osteotomy)
Complication Rate: 15-25% (mostly minor)
Patient Satisfaction: 75-85%

Pedicle Subtraction Osteotomy:

Correction Achieved: 80-90% achieve planned correction (30-40 degrees)
Sagittal Balance: SVA less than 50mm achieved in 85-90%
Pain Relief: 65-75% significant improvement
Functional Improvement: 60-70% meaningful ODI improvement
Fusion Rate: 85-90%
Complication Rate: 40-50% (major complications 10-15%)
Patient Satisfaction: 65-75%

Vertebral Column Resection:

Correction Achieved: 75-85% achieve planned correction (50-70 degrees)
Pain Relief: 60-70% significant improvement
Functional Improvement: 55-65% meaningful improvement
Fusion Rate: 75-85%
Complication Rate: 50-70% (major complications 20-30%)
Patient Satisfaction: 55-65%

Predictors of Success

Positive Predictors:

Appropriate osteotomy selection (match to deformity)
Achievement of solid fusion
Restoration of sagittal balance (SVA less than 50mm, PI-LL within 10 degrees)
Good bone quality (T-score greater than -2.0)
Age less than 65 years
Non-smoker
Single osteotomy (vs multiple or revision)
Realistic expectations

Negative Predictors:

Severe osteoporosis (T-score less than -3.0)
Active smoking
Multiple comorbidities (Charlson index greater than 3)
Revision osteotomy at same level
Chronic opioid use preoperatively
Poor nutritional status (albumin less than 3.5)
Unrealistic expectations (expect complete cure)

Long-Term Outcomes

5-Year Outcomes:

Maintained Correction: 75-85% maintain SVA less than 50mm
Fusion Rate: 85-95% if solid at 1 year
Adjacent Segment Disease: 20-30% develop symptomatic ASD
Reoperation Rate: 15-25%
- PJK (most common reason): 8-12%
- Pseudarthrosis: 3-5%
- Rod fracture: 3-5%
- Infection: 2-3%

10-Year Outcomes:

Limited data due to recent adoption of techniques
Cumulative reoperation rate: 25-35%
Patient satisfaction maintained: 60-70% of those initially satisfied
Adjacent segment degeneration: cumulative 35-45%

Evidence Base

PSO Outcomes in Flatback Deformity

Wang et al. • European Spine Journal (2016)

Key Findings:

1,348 patients undergoing PSO analyzed in systematic review
Mean lumbar lordosis correction was 31.2 degrees
SVA improvement was 86.8mm
Neurological complication rate 11.1% (transient 7.4%, permanent 3.7%)
Fusion rate at 2 years was 87.3%

Clinical Implication: PSO is highly effective for severe sagittal imbalance but carries significant neurological risk. Supports neuromonitoring and meticulous technique as standards of care.

Comparison of SPO vs PSO for Sagittal Imbalance

Cho et al. • Spine (2005)

Key Findings:

Patients with SVA less than 100mm treated with multiple SPOs achieved similar sagittal balance (mean SVA 42mm) as single PSO
Lower complication rate with SPOs (18% vs 39%, p=0.01) for mild-moderate deformity
Patients with SVA greater than 100mm had better correction with PSO

Clinical Implication: Supports algorithm: mild-moderate deformity (SVA less than 100mm) can be treated with multiple SPOs with lower risk; severe deformity (SVA greater than 100mm) requires PSO for adequate correction.

Neuromonitoring Reduces Neurological Injury in PSO

Quraishi et al. • Spine (2015)

Key Findings:

Multimodal neuromonitoring (SSEP + MEP) during PSO reduced neurological complication rate from 15.7% to 6.3% (p=0.02)
MEPs were more sensitive than SSEPs for detecting impending motor deficits (92% vs 71%)

Clinical Implication: Multimodal neuromonitoring significantly reduces neurological injury and should be considered standard of care for PSO and VCR procedures.

VCR for Severe Rigid Deformity

Lenke et al. • Spine (2009)

Key Findings:

VCR achieved mean correction of 55 degrees for severe rigid deformities
Overall complication rate was 54%
Neurological deficits in 17% (permanent 6%, transient 11%)
Fusion rate at 2 years was 81%

Clinical Implication: VCR is effective for severe rigid deformities not correctable with PSO, but complication rate is very high. Patient selection and experienced surgical team are critical.

Cement Augmentation Reduces Screw Loosening in Osteoporotic PSO

Hu et al. • Journal of Neurosurgery: Spine (2018)

Key Findings:

Osteoporotic patients (T-score less than -2.5) undergoing PSO with cement-augmented screws had lower screw loosening rate (4.2% vs 18.7%, p less than 0.01)
Lower proximal junctional kyphosis rate with cement augmentation (12% vs 28%, p=0.04)

Clinical Implication: Supports routine cement augmentation of screws in osteoporotic patients undergoing PSO/VCR to reduce fixation failure and PJK.

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOModerate

Intraoperative Neuromonitoring Changes During PSO

EXAMINER

"You are performing a L3 PSO for flatback deformity in a 62-year-old woman. After completing the vertebral body resection, you begin gradual closure of the osteotomy. At 20 degrees of correction, neurophysiology reports bilateral MEP amplitudes have dropped by 70% compared to baseline. SSEPs are stable. Your patient is hemodynamically stable with MAP of 75 mmHg."

EXCEPTIONAL ANSWER

This is a significant intraoperative neuromonitoring alert indicating impending motor deficit. My immediate response follows a systematic protocol: First, I notify the team that we have a neuromonitoring change and stop all compression on the rods immediately. Second, I communicate with anesthesia to augment blood pressure to MAP of 90-100 mmHg to improve spinal cord perfusion. Third, I release the compression slightly (reduce correction by 5-10 degrees) to relieve any tension on neural elements. Fourth, I wait 10-15 minutes for signals to recover while maintaining elevated blood pressure. Fifth, if MEPs do not return to baseline, I would perform a wake-up test to assess actual motor function. If wake-up test shows motor deficit, I accept the current correction (20 degrees still clinically meaningful) and complete fixation. If wake-up test is normal despite persistent MEP changes, I may cautiously attempt additional gradual correction with continuous monitoring. Patient safety is paramount - neurological preservation takes priority over achieving ideal radiographic correction.

KEY POINTS TO SCORE

MEP changes (greater than 50% amplitude drop) are highly predictive of motor deficit and require immediate action

Stop compression immediately when alert occurs - do NOT continue hoping signals will recover

Augment MAP to 90-100 mmHg to improve spinal cord perfusion (potential ischemia)

Release compression partially to relieve neural tension - may restore signals

Wake-up test is gold standard if signals do not recover - assesses actual motor function

Accept less correction if needed - neurological preservation is paramount

COMMON TRAPS

✗Do NOT ignore MEP changes or continue closure - high risk of permanent motor deficit

✗Do NOT rely on SSEPs alone - MEPs more sensitive for motor pathway monitoring

✗Do NOT assume signals will recover spontaneously - active intervention required

✗Do NOT proceed with full planned correction if signals do not return - accept less correction

✗Do NOT delay wake-up test if signals remain abnormal after intervention - confirm motor function

LIKELY FOLLOW-UPS

"What is the sensitivity and specificity of MEPs for predicting motor deficits?"

"How would you modify your response if SSEPs were also lost?"

"What would you do if wake-up test revealed bilateral leg weakness?"

"Could this complication have been prevented with different technique?"

"How would you counsel the patient postoperatively if permanent deficit occurred?"

VIVA SCENARIOModerate

Osteotomy Selection for Complex Deformity

EXAMINER

"A 58-year-old man with previous L4-S1 fusion presents with progressive inability to stand upright. Standing radiographs show SVA of 135mm, PI-LL mismatch of 38 degrees, and pelvic tilt of 35 degrees. Supine hyperextension film shows minimal change (SVA 125mm). He has moderate osteoporosis (T-score -2.3), controlled diabetes (HbA1c 6.9%), and BMI of 32. He is motivated and has failed 12 months of conservative treatment."

EXCEPTIONAL ANSWER

This patient has severe rigid sagittal imbalance requiring osteotomy for realignment. Based on the magnitude of deformity (SVA 135mm, PI-LL 38 degrees) and rigidity (minimal correction on flexibility films), I would recommend L3 pedicle subtraction osteotomy. My reasoning: First, SVA greater than 100mm and PI-LL greater than 30 degrees typically require 30-40 degree correction which only PSO can achieve in single level. Multiple SPOs would be inadequate given rigidity. Second, L3 is optimal level (below conus medullaris, good bone stock, central lordosis distribution). Third, despite moderate osteoporosis and diabetes, these are manageable with optimization. My preoperative plan includes: 3-6 months of teriparatide for osteoporosis (anabolic bone support), vitamin D supplementation target greater than 40 ng/mL, weight optimization (BMI less than 30 preferred), and glycemic control confirmation. Surgical plan: L3 PSO with dual cobalt-chromium rods (6.35mm), extend fixation T10-pelvis, bilateral iliac screws, cement augmentation of proximal screws given osteoporosis, autograft plus BMP, and multimodal neuromonitoring throughout. I would counsel on complication risk (40-50% overall, neurological 5-11%) and expected outcome (70-80% chance of meaningful improvement in upright posture and function, but not complete cure).

KEY POINTS TO SCORE

Severe sagittal imbalance (SVA greater than 100mm, PI-LL greater than 30) requires PSO for adequate single-level correction

Rigidity on flexibility films (less than 10 degree correction) confirms need for bony osteotomy (PSO) rather than SPOs

L3 is optimal level for PSO - below conus, central lordosis, good bone stock

Osteoporosis and diabetes are relative contraindications requiring optimization but not absolute contraindications

Teriparatide pretreatment 3-6 months enhances fusion and reduces screw loosening in osteoporotic patients

Dual rods, iliac screws, and cement augmentation reduce mechanical complication risk

COMMON TRAPS

✗Do NOT choose multiple SPOs - deformity too severe and rigid, will undercorrect

✗Do NOT proceed without osteoporosis treatment - high risk of screw loosening and PJK

✗Do NOT choose VCR - excessive for this deformity, PSO sufficient and lower risk

✗Do NOT ignore diabetes - ensure HbA1c less than 7.0% for infection prevention and fusion

✗Do NOT underestimate complication risk - this is high-risk surgery requiring realistic counseling

LIKELY FOLLOW-UPS

"How would your plan change if SVA was 180mm (requiring greater than 50 degrees correction)?"

"What if DEXA showed severe osteoporosis (T-score -3.5)?"

"If patient refused teriparatide due to cost, would you still proceed?"

"How would you modify technique if patient had prior L3 laminectomy?"

"What would you tell patient about likelihood of achieving normal upright posture?"

Exam Day Cheat Sheet

MCQ Practice Points

Exam Pearl

Q: How much sagittal correction does each type of spinal osteotomy provide?

A: SPO/Ponte osteotomy (Grade 1-2): ~10° per level (posterior column only). PSO (pedicle subtraction osteotomy, Grade 3): 25-35° per level (all three columns). VCR (vertebral column resection, Grade 4-6): greater than 40° per level, unlimited correction. Choose based on correction needed and deformity type.

Exam Pearl

Q: What is the key anatomical difference between SPO and PSO?

A: SPO (Smith-Petersen): Resects posterior elements only; correction through disc space opening anteriorly (hinges on ALL). Requires mobile anterior column. PSO: Resects pedicles and wedge of vertebral body; closure is bone-on-bone, no disc involvement. PSO preferred when anterior column fused or osteoporotic.

Exam Pearl

Q: What is the major complication risk difference between PSO and VCR?

A: PSO blood loss: 1.5-3L average; VCR blood loss: 3-5L average. Neurological risk: PSO ~5-10%, VCR ~15-20%. VCR requires circumferential decompression with temporary spinal cord instability. Both require neuromonitoring. VCR reserved for severe rigid deformities, tumors, or failed prior surgery.

Exam Pearl

Q: What is the Schwab classification of spinal osteotomies?

A: Grade 1: Partial facetectomy. Grade 2: Complete facetectomy (Ponte). Grade 3: PSO through single vertebra. Grade 4: VCR single vertebra. Grade 5: VCR two adjacent vertebrae. Grade 6: VCR three+ vertebrae. Higher grades = more correction possible but higher morbidity. Guides surgical planning.

Exam Pearl

Q: What are the indications for pedicle subtraction osteotomy (PSO)?

A: Fixed sagittal imbalance greater than 10-15cm, ankylosed spine (AS, DISH), failed prior fusion with kyphosis, iatrogenic flatback syndrome. Performed at apex of deformity or L3 (L2-L4 acceptable). Contraindicated at previously instrumented/fused levels without hardware removal. Goal: Restore SVA to within 5cm of sacrum.

Australian Context

Australian Epidemiology and Management

Complex Spine Surgery in Australia:

Spinal osteotomy procedures concentrated at major tertiary centres (Royal North Shore, St Vincent's Melbourne, Royal Adelaide, Princess Alexandra Brisbane, Royal Perth)
Fellowship-trained complex spine surgeons perform majority of PSO/VCR procedures
Australian Spine Society (AOSS) maintains registry for deformity surgery outcomes
Multidisciplinary spine deformity clinics at major centres coordinate complex cases

RACS Orthopaedic Training Relevance:

Spinal osteotomies are high-yield FRACS Orthopaedic examination topics
Key exam focus: Schwab classification, osteotomy selection based on deformity, neuromonitoring principles
Viva scenarios commonly test response to neuromonitoring changes and patient selection
Understanding of biomechanical principles (correction potential, axis of rotation) is examined

Private Health Insurance:

Complex spine surgery requires prosthesis billing (rods, screws, cages)
Prostheses List items covered under hospital insurance
Extended ICU and hospital stay typical for PSO/VCR (7-14 days)

AHPRA and TGA Considerations:

Spinal implants (pedicle screws, rods, cages) require TGA registration
BMP (bone morphogenetic protein) usage for fusion augmentation is off-label in spine
Informed consent must address specific TGA-registered implant details

Training Pathway:

AOSS Complex Spine Surgery Fellowship (1-2 years post-FRACS)
International fellowship options (USA scoliosis centres, AOSpine fellowship)
Minimum 50 PSO cases before independent practice recommended

Neuromonitoring Services:

Dedicated intraoperative neurophysiology technicians required
Available at all major Australian centres performing complex osteotomies
SSEP and MEP monitoring standard of care for PSO/VCR

High-Yield Exam Summary

Osteotomy Essentials - Match Type to Deformity

•SPO: Posterior column only, 10 degrees per level, flexible deformity, anterior column intact as hinge, low risk (1-3% neuro)
•PSO: All three columns, 30-40 degrees per level, rigid flatback/severe sagittal imbalance, moderate risk (5-11% neuro)
•VCR: Complete vertebrectomy, 50-70 degrees, severe rigid angular deformity, high risk (10-25% neuro)
•Selection: SVA less than 100mm flexible → SPOs; SVA 100-150mm rigid → PSO; SVA greater than 150mm or angular → PSO + SPOs or VCR

PSO Optimal Level Selection

•L3 most common (below conus medullaris at T12-L2, cauda equina tolerates manipulation better than cord, good bone stock)
•L2 acceptable if L3 unfavorable anatomy
•Avoid L4 (too close to L5-S1, lordosis distribution), avoid thoracic (spinal cord present, myelopathy risk)
•Avoid T12-L2 (conus medullaris, high risk)
•Flexibility films assess rigidity (less than 10 degree correction = rigid, needs bony osteotomy)

PSO Stepwise Technique - TECHNIQUE Mnemonic

•T-Temporary rods after all instrumentation
•E-Expose and remove posterior elements (laminectomy L3, facetectomy L2-L3 and L3-L4)
•C-Cut pedicles carefully (preserve L3 nerve roots)
•H-Hollow vertebral body (30-40 degree wedge, preserve 1-2mm anterior cortex)
•N-Neuromonitoring active (SSEP, MEP) throughout
•I-Instrument with permanent rods (gradual compression closes wedge)
•Q-Quality check fluoroscopy, U-Utilize cross-links (stability)
•E-Elevate blood pressure (MAP greater than 85) during closure

Neuromonitoring and Response - MONITOR Mnemonic

•M-Maintain MAP greater than 85 mmHg (cord perfusion)
•O-Observe SSEP and MEP continuously
•N-Notify surgeon ANY signal changes immediately
•I-Incremental closure (gradual, not sudden)
•T-Test wake-up if signals lost
•O-Optimize BP to 90-100 if neuro changes
•R-Release correction if signals do not recover (safety first)
•Alert criteria: MEP greater than 50% amplitude drop; SSEP greater than 50% amplitude drop or greater than 10% latency increase

Patient Selection - OSTEOTOMY Mnemonic

•O-Objectives clear (restore balance, improve function)
•S-Sagittal imbalance severe (SVA greater than 50mm, PI-LL greater than 20)
•T-Trial conservative failed (minimum 6 months)
•E-Expectations realistic (60-70% improvement not cure)
•O-Osteoporosis optimized (DEXA, teriparatide if T-score less than -2.5)
•T-Type matches deformity, O-Other comorbidities controlled
•M-Medical fitness confirmed, Y-Young enough (age less than 75 preferred)
•Absolute contraindications: active infection, severe osteoporosis untreated, prohibitive medical risk

Complications by Type

•SPO: 1-3% neuro, 15-25% overall complications (mostly minor), 90-95% fusion
•PSO: 5-11% neuro, 40-50% overall complications (major 10-15%), 85-90% fusion, 5-10% rod fracture at 2 years
•VCR: 10-25% neuro, 50-70% overall complications (major 20-30%), 75-85% fusion, massive blood loss (2-5 liters average)
•Medical complications all types: DVT/PE 3-5%, infection 3-8%, PJK 20-40%

Intraoperative Pearls

•Four-rod technique: temporary rods during resection, permanent rods for closure
•Cell saver: autotransfusion reduces allogeneic blood (important in PSO/VCR)
•Hypotensive anesthesia during resection: MAP 65-70 reduces blood loss
•Maintain MAP greater than 85 during closure: spinal cord perfusion
•Gradual closure: 5-10 degrees at a time, monitor signals, wait 2-3 minutes between compressions
•Wake-up test ready: if MEPs lost and do not recover, confirms motor function

Expected Outcomes

•SPO: 90-95% achieve correction, 70-80% pain relief, 75-85% satisfaction, 90-95% fusion
•PSO: 80-90% achieve correction (SVA less than 50mm in 85-90%), 65-75% pain relief, 85-90% fusion
•VCR: 75-85% achieve correction, 60-70% pain relief, 55-65% satisfaction, 75-85% fusion
•Positive predictors: appropriate osteotomy selection, solid fusion, SVA less than 50mm restored, age less than 65, non-smoker
•Negative predictors: severe osteoporosis, smoking, multiple comorbidities, revision at same level

Postoperative Management

•ICU first 24-48 hours: neuro checks every 1-2 hours, maintain MAP greater than 85 mmHg
•Early mobilization: POD1 sit, POD2 stand/walk, reduces DVT/pneumonia/ileus
•TLSO brace 12 weeks for PSO/VCR
•DVT prophylaxis: mechanical POD0, chemical POD1 (after drain removal)
•Follow-up: 6 weeks radiographs, 12 weeks discontinue brace, 12 months CT confirm fusion
•Urgent MRI if neurological deficit: rule out hematoma, hardware malposition, cord ischemia

Examiner Expectations

•Demonstrate systematic approach to osteotomy selection based on deformity characteristics
•Explain biomechanical principles (axis of rotation, columns affected, correction potential)
•Show detailed technical knowledge of PSO steps (not just 'do osteotomy')
•Emphasize neuromonitoring and response to changes (safety-focused)
•Discuss realistic outcomes (PSO 65-75% pain relief, 40-50% complication rate, not cure)
•Show judgment in patient selection; explain when NOT to operate

Spinal Osteotomy Techniques: PSO, VCR, and SPO

High Yield Overview