Loss of lumbar lordosis causing forward trunk lean with inability to stand upright
- Flatback = loss of lumbar lordosis causing sagittal imbalance with forward trunk lean
- SVA (sagittal vertical axis): distance from C7 plumb line to S1; normal under 5cm
- PI-LL mismatch: difference between pelvic incidence and lumbar lordosis; normal under 10 degrees
- Three-column osteotomies: SPO (10 degrees), PSO (30 degrees), VCR (40 degrees)
- Iatrogenic most common cause: distraction instrumentation (Harrington rods)
- “Patients cannot stand upright without compensation (knee flexion, hip extension)
- “ODI and SF-36 correlate with SVA - most important predictor of disability
- “Always assess pelvic compensation (pelvic tilt, pelvic incidence-lumbar lordosis)
- “Rod fracture risk high if SVA not corrected adequately
Flatback Syndrome
Sagittal Vertical Axis (SVA) is the MOST important parameter! Measure from C7 plumb line to posterosuperior S1. Normal under 5cm. Symptoms when over 5cm. Disability severe when over 10cm. This predicts patient outcomes better than any other parameter.
Pelvic Incidence minus Lumbar Lordosis should be under 10 degrees. PI is FIXED (anatomic), LL is VARIABLE (can lose with degeneration). Mismatch over 10 degrees = sagittal imbalance requiring correction. Target: PI-LL under 10 degrees.
Osteotomies by correction power: SPO (Smith-Petersen, posterior column) = approximately 10 degrees/level, PSO (Pedicle Subtraction, three-column) = approximately 30 degrees/level, VCR (Vertebral Column Resection) = 40 degrees or more per level. PSO most common for flatback. VCR for severe/rigid deformities.
Harrington rod instrumentation was the classic cause (distraction without lordosis preservation). Now: long fusions to sacrum without lordosis, adjacent segment degeneration, pseudarthrosis. Always assess prior hardware and fusion mass on imaging.
Overview and Epidemiology
Flatback syndrome is a debilitating spinal deformity characterized by loss of normal lumbar lordosis, resulting in sagittal plane imbalance where patients cannot maintain an upright posture without significant compensatory mechanisms.
Definition
Flatback syndrome occurs when the lumbar spine loses its normal lordotic curvature (typically 40-60 degrees from L1-S1), resulting in positive sagittal balance where the C7 plumb line falls anterior to the posterosuperior corner of S1.
Key Concept: Normal spine in sagittal plane = head centered over pelvis with minimal energy expenditure. Flatback = head anterior to pelvis requiring constant muscular compensation.
Epidemiology
Prevalence
- Value
- 20-40% after Harrington rod instrumentation
- Value
- 5-10% after modern spinal fusion
- Value
- 50-70 years (iatrogenic), variable (degenerative)
- Value
- Female predominance (2:1) - more fusions for scoliosis
Risk Factors
- Specific Factors
- Harrington rods, long fusion to sacrum, flat rod contouring
- Specific Factors
- Disc collapse, compression fractures, ankylosing spondylitis
- Specific Factors
- Pseudarthrosis, junctional kyphosis, hardware failure
- Specific Factors
- Osteoporosis, smoking, obesity, prior laminectomy
Historical Context
Harrington Era (1960s-1990s): Distraction instrumentation for scoliosis correction. Straightened spine in coronal plane but ELIMINATED lumbar lordosis. Result: epidemic of flatback syndrome. Modern instrumentation preserves lordosis with contoured rods and pedicle screw fixation.
Pathophysiology
Sagittal Balance Concepts
Normal Sagittal Alignment
The spine maintains sagittal balance through reciprocal curves:
- Cervical lordosis: 20-40 degrees
- Thoracic kyphosis: 20-40 degrees
- Lumbar lordosis: 40-60 degrees (L1-S1)
Energy Efficiency: When C7 plumb line falls within 2-5cm of posterosuperior S1, minimal muscular effort required to maintain upright posture.
Pelvic Parameters (CRITICAL for Exam)
- Definition
- Angle from S1 midpoint to hip axis
- Normal Range
- 35-80 degrees
- Clinical Significance
- FIXED anatomic parameter (cannot change)
- Definition
- Vertical to S1-hip axis line
- Normal Range
- 10-25 degrees
- Clinical Significance
- VARIABLE - increases with compensation
- Definition
- S1 endplate to horizontal
- Normal Range
- 30-50 degrees
- Clinical Significance
- VARIABLE - decreases in flatback
- Definition
- Mathematical relationship
- Normal Range
- Always true
- Clinical Significance
- Use to check measurement accuracy
Lumbar Lordosis (LL): Should approximately equal Pelvic Incidence (PI-LL under 10 degrees)
Pathophysiology of Imbalance
Stage 1: Loss of Lordosis
- Iatrogenic: Flat rod contouring, distraction forces
- Degenerative: Disc collapse, compression fractures
- Result: Lumbar lordosis decreases below PI
Stage 2: Pelvic Compensation
- Pelvis rotates posteriorly (increased pelvic tilt)
- Sacral slope decreases
- Goal: Bring C7 plumb line back over sacrum
- Energy cost: Moderate increase
Stage 3: Hip and Knee Compensation
- Pelvic compensation exhausted
- Hip extension (limited by hip flexors)
- Knee flexion (to shift center of mass posterior)
- Energy cost: Severe increase, early fatigue
Stage 4: Decompensation
- All compensatory mechanisms exhausted
- Fixed forward trunk lean
- Inability to stand upright without support
- Severe disability
Compensation Exhaustion: Patients with high pelvic tilt (over 25 degrees) have exhausted pelvic compensation. These patients have SEVERE disability and limited reserve for further degeneration. Surgical correction should restore balance to avoid progression.
Etiologies
Iatrogenic Flatback (Most Common)
Harrington Rod Era
- Distraction instrumentation without lordosis preservation
- Long fusions (often to L5 or sacrum)
- Flat rod contouring (no sagittal profile)
- Result: Complete loss of lumbar lordosis
Modern Instrumentation Issues
- Undercorrection of lordosis in long fusions
- Flat rod placement in degenerative fusions
- Pseudarthrosis with rod fracture and kyphosis
- Adjacent segment degeneration above fusion
Prevention Strategies (Modern)
- Contoured rods matching normal lordosis (60-70 degrees L1-S1)
- Pedicle screw fixation for lordosis control
- Interbody cages with lordotic angles (20-30 degrees)
- Avoid long fusions unless necessary
This section describes the causes of iatrogenic flatback syndrome.
A classic spine-deformity examiner question that this topic must answer: lordosis DISTRIBUTION matters as much as its magnitude. The Roussouly classification describes four normal sagittal lumbar morphotypes defined by the sacral slope, each with a characteristic lordosis magnitude, apex and number of vertebrae in the curve:
- Type 1 - low sacral slope (under approximately 35 degrees): a short, sharply-angled lower-lumbar hyperlordosis with a low apex (near L5) and a thoracolumbar kyphosis above. Low pelvic incidence.
- Type 2 - low sacral slope but a flat, low-magnitude lordosis ("flat back" morphotype). Low pelvic incidence. This shape is the most prone to degenerative disc disease and to degenerative flatback - the spine has little lordotic reserve to lose.
- Type 3 - average sacral slope (approximately 35 to 45 degrees): a well-balanced, harmonious lordosis with the apex at L4. The most common and most forgiving morphotype.
- Type 4 - high sacral slope (over approximately 45 degrees) and high pelvic incidence: a long, curved hyperlordosis with a high apex (L3 or above) and many vertebrae recruited into the curve.
Why it matters for flatback correction: restoring the correct total lumbar lordosis is not enough - the lordosis must be distributed correctly (the right apex and the right proportion in the lower arc, where roughly two-thirds of lordosis normally sits below L4). A correction that gives an adequate number of degrees but the wrong shape (for example a uniform, low-apex lordosis in a patient whose pelvic incidence demands a Type 3 or 4 distribution) leaves the construct mismatched to the patient's ideal Roussouly type and is a recognised driver of proximal junctional kyphosis and mechanical failure. Plan to recreate the patient's predicted ideal morphotype, not simply a target number.
Clinical Presentation
Symptoms
Cardinal Symptom: Forward Trunk Inclination
Patients describe:
- Inability to stand upright
- "Looking at the ground" when walking
- Needing to lean on shopping cart or walker
- Severe fatigue with standing or walking
Pain Distribution
- Mechanism
- Constant isometric contraction
- Characteristics
- Burning, aching, fatigue
- Mechanism
- Hip extension compensation
- Characteristics
- Cramping, tightness
- Mechanism
- Flexion compensation
- Characteristics
- Aching, early arthritis
- Mechanism
- Gluteal fatigue
- Characteristics
- Weakness, pain with standing
Functional Limitations
- Standing tolerance: Often under 15-30 minutes
- Walking distance: Limited by fatigue, not neurogenic claudication
- Social impact: Unable to make eye contact, difficulty with activities
- ADL impairment: Cannot stand to cook, shop, socialize
Physical Examination
Inspection
- Significance
- Cannot stand upright without support
- Significance
- Compensatory mechanism
- Significance
- Limited by tight hip flexors
- Significance
- Shuffling, antalgic, requires assistive device
Palpation
- Paraspinal muscle spasm and tenderness
- Loss of lumbar lordotic curve
- Step-off if spondylolisthesis present
- Hardware palpable if prior surgery
Range of Motion
- Lumbar extension: Severely limited or absent
- Lumbar flexion: Often preserved
- Hip extension: Limited (Thomas test positive)
Neurologic Examination
- Usually normal (not a neurologic condition)
- Assess for radiculopathy if foraminal stenosis
- Assess for myelopathy if cervical compensation
Special Tests
- Technique
- Patient flexes forward, attempts to stand upright
- Positive Finding
- Cannot achieve upright position without knee flexion
- Technique
- Patient stands with back to wall, attempts to touch wall with back of head
- Positive Finding
- Head far anterior to wall (over 15cm abnormal)
- Technique
- Patient bends forward from waist
- Positive Finding
- Assess coronal deformity if scoliosis present
Impact on Quality of Life
Patient-Reported Outcomes
Studies show:
- ODI (Oswestry Disability Index) correlates strongly with SVA
- SF-36 physical function severely impaired
- Depression and anxiety common (chronic pain, disability)
Correlation with SVA
- Disability Level
- Minimal disability
- Disability Level
- Moderate disability
- Disability Level
- Severe disability
Investigations
Radiographic Assessment (ESSENTIAL)
Standing Full-Length Lateral Spine Radiograph
Technique Requirements:
- True standing position (no leaning, no support)
- Arms positioned: Fists on clavicles or grasping horizontal bars
- Film includes: Skull to femoral heads
- Cassette: 36-inch length minimum
CRITICAL: Radiographs MUST be taken STANDING. Supine films cannot assess sagittal balance and will underestimate deformity. Patients must stand unsupported with arms positioned to clear thoracic spine.
Key Radiographic Measurements
Sagittal Vertical Axis (SVA)
- Technique
- Plumb line from C7 vertebral body center to posterosuperior S1
- Normal
- Under 5cm
- Abnormal
- Over 5cm
- Technique
- Positive = C7 anterior to S1 (flatback)
- Normal
- 0-5cm
- Abnormal
- Over 10cm = severe
Pelvic Parameters
- Measurement
- Angle: S1 midpoint to hip axis, perpendicular to S1
- Normal
- 35-80 degrees
- Flatback
- FIXED (anatomic)
- Measurement
- Angle: vertical to line from S1 to hip axis
- Normal
- 10-25 degrees
- Flatback
- Over 25 degrees (compensated)
- Measurement
- Angle: S1 endplate to horizontal
- Normal
- 30-50 degrees
- Flatback
- Under 30 degrees
Lumbar Lordosis (LL)
- Measurement: Cobb angle from superior endplate L1 to superior endplate S1
- Normal: 40-60 degrees (approximately equals PI)
- Flatback: Under 30 degrees
PI-LL Mismatch
- Calculation: Pelvic Incidence minus Lumbar Lordosis
- Normal: Under 10 degrees
- Symptomatic: Over 10 degrees
- Severe: Over 20 degrees
PI-LL Mismatch is the KEY surgical parameter: Goal of surgery is to restore PI-LL to under 10 degrees. For example, if PI = 60 degrees, target LL = 50-70 degrees (within 10 degrees). This predicts outcomes better than SVA alone.
Advanced Imaging
CT Scan
Indications:
- Surgical planning (bony anatomy, pedicle size)
- Assessment of prior fusion mass
- Hardware evaluation (loosening, fracture)
- Osteotomy level selection
MRI
Indications:
- Assess neural compression (stenosis, radiculopathy)
- Disc degeneration and remaining disc health
- Pseudarthrosis evaluation (fluid signal at fusion site)
- Spinal cord integrity if myelopathy suspected
Flexion-Extension Radiographs
- Assess mobility at adjacent segments
- Identify pseudarthrosis (motion at fusion site)
- Plan osteotomy location (mobile vs. fused segments)
Classification of Flatback Deformity
Ames-ISSG Classification (Most Commonly Used)
Based on SVA and PT:
- SVA
- Under 5cm
- PT
- Under 25 degrees
- Interpretation
- Compensated, minimal symptoms
- SVA
- 5-10cm
- PT
- Under 25 degrees
- Interpretation
- Mild imbalance
- SVA
- Over 10cm
- PT
- Under 25 degrees
- Interpretation
- Severe imbalance, compensation failing
- SVA
- Any
- PT
- Over 25 degrees
- Interpretation
- Severe, pelvic compensation exhausted
Surgical Implications:
- Type 0: Conservative management
- Type I: Consider surgery if symptomatic
- Type II-III: Surgery usually indicated
SVA is the headline parameter, but examiners increasingly expect two newer measures that overcome SVA's weaknesses.
T1 Pelvic Angle (TPA) is the angle subtended at the femoral head axis between a line to the centroid of the T1 vertebral body and a line to the centre of the S1 endplate. It effectively combines trunk inclination and pelvic tilt into one number. Its key advantage over SVA is that it is position-independent: SVA can be falsely "normalised" by a patient recruiting compensation (pelvic retroversion, knee flexion), so a measured SVA may underestimate the true deformity, whereas TPA captures both the trunk lean and the pelvic compensation and is not erased by that recruitment. A TPA of over approximately 20 degrees indicates severe deformity; the realignment target is roughly under 14 degrees.
The GAP score (Global Alignment and Proportion) is a proportional, pelvic-incidence-based score rather than an absolute threshold. It combines relative pelvic version, relative lumbar lordosis, the lordosis distribution index (echoing the Roussouly principle that the apex and lower-arc proportion matter), relative spinopelvic alignment, and an age factor, and grades the reconstruction as proportioned, moderately disproportioned, or severely disproportioned. Its value is predictive: a disproportioned construct carries a substantially higher rate of mechanical complications (rod fracture, proximal junctional kyphosis, pseudarthrosis), so aiming for a proportioned GAP result - not merely an SVA under 5cm - is the modern planning goal. Both measures reinforce the same lesson as age-adjusted targets: alignment must be individualised to the patient's pelvic incidence and age, not forced to a single universal number.
Management Algorithm
Non-Operative Treatment
Efficacy: Limited for established flatback syndrome. May provide symptomatic relief but does NOT correct deformity.
Physiotherapy
Goals:
- Strengthen core musculature
- Improve hip flexor flexibility
- Maintain existing lumbar motion
Exercises:
- Examples
- Planks, bridges, dead bugs
- Benefit
- Improve paraspinal endurance
- Examples
- Thomas stretch, kneeling lunge
- Benefit
- Reduce compensatory hip extension
- Examples
- Seated hamstring stretch
- Benefit
- Allow pelvic rotation
- Examples
- Wall slides, chin tucks
- Benefit
- Awareness and positioning
Limitations: Cannot restore lost lordosis or correct fixed deformity.
Medications
- Examples
- Ibuprofen, naproxen
- Use
- Muscle inflammation, pain
- Limitations
- GI side effects, limited efficacy
- Examples
- Cyclobenzaprine
- Use
- Paraspinal spasm
- Limitations
- Sedation, not for long-term
- Examples
- Gabapentin, pregabalin
- Use
- If radicular component
- Limitations
- Minimal benefit for mechanical pain
Interventional Procedures
Epidural Steroid Injections
- Indication: Radiculopathy from foraminal stenosis
- Efficacy: Temporary relief (weeks to months)
- NOT effective for mechanical back pain from imbalance
Facet Injections
- Indication: Facet-mediated pain
- Efficacy: Variable, temporary
- NOT a treatment for sagittal imbalance
Assistive Devices
- Use
- Unloads spine, allows forward lean
- Limitation
- Dependence, social stigma
- Use
- Minimal support
- Limitation
- Insufficient for severe flatback
- Use
- May reduce pain
- Limitation
- Does NOT correct deformity
Natural History
Untreated Flatback Syndrome:
- Progressive worsening of SVA and PT
- Increasing disability and pain
- Adjacent segment degeneration above prior fusion
- Hip and knee arthritis from compensatory postures
Indications for Surgery:
- Failed conservative management (3-6 months trial)
- Severe disability (ODI over 40)
- SVA over 5cm with symptoms
- PI-LL mismatch over 10 degrees with symptoms
- Progressive deformity
Conservative management provides symptom control but rarely resolves flatback.
Surgical Management
Goals of Surgical Correction
Radiographic Goals:
- SVA under 5cm (ideally 0-3cm)
- PI-LL mismatch under 10 degrees
- Restore lumbar lordosis to match pelvic incidence
- Maintain coronal balance
Clinical Goals:
- Allow upright posture without compensation
- Reduce pain and disability
- Improve walking tolerance and ADLs
- Minimize complications
Surgical Options Overview
Smith-Petersen Osteotomy (SPO)
Type: Posterior column osteotomy (Schwab Grade I)
Technique:
- Remove inferior facet, superior facet, and ligamentum flavum
- Creates V-shaped gap in posterior elements
- Closes gap to create lordosis
- REQUIRES mobile anterior column (disc or pseudarthrosis)
Correction: Approximately 10 degrees per level (cumulative across multiple levels)
Indications:
- Mild sagittal imbalance (SVA under 10cm)
- PI-LL mismatch under 20 degrees
- Mobile anterior column present
- Multiple level correction planned
Advantages:
- Lowest complication rate
- Preserves vertebral body
- Can be performed at multiple levels
Disadvantages:
- Limited correction per level
- Requires mobile disc
- Risk of anterior column fracture if forced closure
Complications:
- Neurologic injury: 2-5%
- Vertebral body fracture: 5-10%
- Inadequate correction: Common if used alone
This describes the Smith-Petersen posterior column osteotomy technique.
Surgical Planning
Preoperative Assessment:
- Assessment
- 5-10cm
- Surgical Plan
- Single-level PSO may suffice
- Assessment
- Over 10cm
- Surgical Plan
- May need 2-level PSO or PSO + SPO
- Assessment
- 20-30 degrees
- Surgical Plan
- Single-level PSO (30 degrees correction)
- Assessment
- Over 40 degrees
- Surgical Plan
- Consider VCR or 2-level PSO
- Assessment
- Solid fusion mass
- Surgical Plan
- Osteotomy through fusion or adjacent
- Assessment
- DEXA T-score under -2.5
- Surgical Plan
- Optimize bone health, consider cement augmentation
Osteotomy Level Selection:
- Advantages
- Large vertebral body, high lordosis potential
- Disadvantages
- High in lumbar spine, junctional stress
- Advantages
- Most common PSO level, large body, safer
- Disadvantages
- Moderate lordosis contribution
- Advantages
- Good lordosis, mid-lumbar
- Disadvantages
- Smaller body, L5 root at risk
- Advantages
- Maximum lordosis potential
- Disadvantages
- Small body, sacral roots at risk, NOT recommended
Most Common PSO Level: L3 (balance of safety and correction)
Surgical Technique: Pedicle Subtraction Osteotomy (PSO)
Patient Positioning:
- Prone on Jackson table or radiolucent frame
- Hips extended (allows lordosis)
- Arms abducted 90 degrees
- Neuromonitoring leads placed
Instrumentation:
- Exposure: Midline incision, subperiosteal dissection
- Screw placement: Pedicle screws 3-4 levels above and below osteotomy
- Temporary rods: Place to maintain stability
Osteotomy Steps:
- Laminectomy: Complete removal of lamina, spinous process at osteotomy level
- Facetectomy: Remove inferior and superior facets bilaterally
- Pedicle resection: Remove pedicles bilaterally (identify nerve roots)
- Posterior body resection:
- Remove posterior 1/3 to 1/2 of vertebral body
- Create 30-40 degree wedge
- Taper resection laterally (egg-shaped)
- Nerve root decompression: Mobilize nerve roots, protect during closure
Closure:
- Remove temporary rods
- Place final rods (pre-contoured with lordosis)
- Close osteotomy site SLOWLY:
- 1-2mm at a time
- Check neuromonitoring after each increment
- Use cantilever maneuver
- Compress instrumentation
- Decorticate fusion bed
- Apply bone graft and BMP
Closure and Hemostasis:
- Large drains (hemovac)
- Layered closure over drains
- Subfascial drain placement
Operative time for single-level PSO is typically 4-6 hours.
Complications
Intraoperative Complications
Neurologic Injury
- Incidence
- 5-10%
- Mechanism
- Direct injury, ischemia, hematoma
- Management
- Stop closure, release compression, imaging
- Incidence
- 15-25%
- Mechanism
- Nerve root traction
- Management
- Often transient, monitor
- Incidence
- 1-2%
- Mechanism
- Severe canal compromise
- Management
- Immediate decompression
Vascular Injury
- Incidence
- 0.5-1%
- Risk Factors
- PSO at L4-5, osteoporotic collapse
- Management
- Vascular surgery consult, open repair
- Incidence
- 0.5-1%
- Risk Factors
- Anterior perforation
- Management
- Direct repair, difficult access
- Incidence
- 5-10%
- Risk Factors
- Lateral dissection
- Management
- Usually self-limiting, electrocautery
Hemorrhage
- Average blood loss PSO: 1-3 liters
- Average blood loss VCR: 3-5 liters
- Transfusion rate: 70-90%
- Consider cell saver, antifibrinolytics (tranexamic acid)
Early Postoperative Complications (Under 6 Weeks)
Neurologic
- New or worsening deficit: 10-30% (most recover)
- Epidural hematoma: 2-5% (may require evacuation)
- Nerve root injury: 5-10% (usually transient)
Cardiopulmonary
- Incidence
- 5-10%
- Risk Factors
- Long surgery, immobility
- Prevention
- Chemoprophylaxis, SCDs
- Incidence
- 5-8%
- Risk Factors
- Prolonged intubation, pain
- Prevention
- Early mobilization, incentive spirometry
- Incidence
- 10-20%
- Risk Factors
- Bowel retraction, narcotics
- Prevention
- Early feeding, bowel regimen
Wound Complications
- Infection (superficial): 5-10%
- Infection (deep): 3-5%
- Seroma/hematoma: 5-10%
- CSF leak: 3-5%
Late Complications (Over 6 Weeks)
Proximal Junctional Kyphosis (PJK)
- Details
- 20-40% after PSO
- Details
- Kyphosis over 10 degrees at upper instrumented vertebra (UIV)
- Details
- Stopping at thoracolumbar junction, osteoporosis, overcorrection
- Details
- Extend to upper thoracic spine (T9-T10), avoid overcorrection
- Details
- Extension of fusion if symptomatic or progressive
Rod Fracture
- Details
- 10-20% overall (higher if SVA over 5cm postop)
- Details
- 6 months to 2 years
- Details
- Undercorrection (SVA over 5cm), pseudarthrosis, single rods
- Details
- Adequate SVA correction, dual rods, solid fusion
- Details
- Revision if symptomatic or progressive deformity
Pseudarthrosis
- Incidence: 10-20% at osteotomy site
- Risk factors: Smoking, osteoporosis, infection, rod fracture
- Diagnosis: CT (motion, lucency), rod fracture
- Treatment: Revision fusion, BMP, anterior support
Implant Failure
- Screw pullout: 5-10% (osteoporosis, overcorrection forces)
- Screw fracture: 2-5%
- Cross-link fracture: 5-10%
Complication Prevention Strategies
- Prevention Strategy
- Slow closure, neuromonitoring, adequate decompression, avoid overstretching
- Prevention Strategy
- Careful anterior dissection, stay midline, palpate aorta
- Prevention Strategy
- Adequate SVA correction (under 5cm), dual rods, solid fusion
- Prevention Strategy
- Extend to upper thoracic, avoid overcorrection, prophylactic vertebroplasty UIV
- Prevention Strategy
- Prophylactic antibiotics, meticulous hemostasis, vancomycin powder
- Prevention Strategy
- BMP, bone graft, avoid smoking, optimize nutrition
Postoperative Care
Immediate Postoperative (Day 0-2)
ICU Monitoring:
- Hemodynamic stability (blood loss often significant)
- Neurologic examination every 2 hours
- Drain output monitoring
- Pain control (PCA, epidural)
Early Mobilization:
- Out of bed to chair Day 1 (if stable)
- Walking with PT Day 2-3
- No brace typically required (rigid internal fixation)
Hospital Stay (Days 3-7)
Monitoring:
- Daily neurologic examination
- Drain removal when output under 30mL per 8 hours
- Early radiographs (AP and lateral) to assess alignment
- Transition to oral pain medications
Physical Therapy:
- Progressive ambulation
- Core strengthening (isometric)
- ADL training
- Stair climbing prior to discharge
Discharge Criteria:
- Hemodynamically stable
- Neurologically stable or improving
- Pain controlled on oral medications
- Ambulating independently or with walker
- Drains removed
Outpatient Follow-Up
Timeline:
- Assessment
- Wound check, suture removal
- Imaging
- None (unless concern)
- Assessment
- Clinical exam, pain assessment
- Imaging
- AP/Lateral X-rays (standing)
- Assessment
- Neurologic exam, function
- Imaging
- AP/Lateral X-rays (standing)
- Assessment
- Function, return to activities
- Imaging
- AP/Lateral X-rays
- Assessment
- Final assessment
- Imaging
- AP/Lateral X-rays, CT if concern for fusion
- Assessment
- Long-term outcome
- Imaging
- As needed
Radiographic Assessment:
- SVA (goal: under 5cm)
- PI-LL mismatch (goal: under 10 degrees)
- Hardware integrity (rod fracture?)
- Fusion mass (bridging bone?)
- Proximal junctional kyphosis assessment
Activity Restrictions
- Restriction Period
- No lifting over 10 lbs for 3 months
- Rationale
- Protect fusion, prevent hardware failure
- Restriction Period
- No driving for 6 weeks (narcotics)
- Rationale
- Safety, pain control
- Restriction Period
- 3 months
- Rationale
- Depends on pain, function
- Restriction Period
- 6-12 months
- Rationale
- Heavy labor risk to fusion
- Restriction Period
- Light activities 6 months, full 1 year
- Rationale
- Fusion maturation
Bracing
Typically NOT Required:
- Rigid pedicle screw fixation provides stability
- Bracing does NOT improve fusion rates in modern instrumentation
- May use soft lumbar corset for comfort (not structural)
Exceptions:
- Osteoporotic bone (concern for screw pullout)
- Extended laminectomy (concern for instability)
- Patient preference for comfort
Postoperative care focuses on neurologic monitoring and progressive mobilization.
Guidelines, Registries & Global Practice
Global Epidemiology
Flatback historically affected 20-40% of patients after Harrington distraction instrumentation; with lordosis-preserving pedicle screw constructs the rate of clinically significant iatrogenic flatback has fallen to roughly 5-10% after long fusion. Adult spinal deformity overall affects up to 60% of people over 60 years on radiographic survey, with a female predominance reflecting the higher rate of scoliosis fusion.
Side-by-Side Society and Group Guidance
- Position on Sagittal Realignment
- Classification grading by SVA, PT and PI-LL; targets SVA under 4cm, PT under 20-25 degrees, PI-LL under 10 degrees
- Position on Sagittal Realignment
- Endorses age-adjusted alignment targets (older patients tolerate higher SVA/PI-LL); three-column osteotomy for fixed deformity
- Position on Sagittal Realignment
- Maintains adult deformity outcome registry; emphasises sagittal over coronal correction (Glassman 2005)
- Position on Sagittal Realignment
- Specialist commissioning only; deformity correction confined to tertiary units with neuromonitoring
Registry and Outcome Notes
- Multicentre deformity databases (e.g. ISSG, European Spine Study Group) report symptomatic rod fracture of 6-8% overall and approximately 16% after PSO, concentrated at the osteotomy site.
- Reoperation rates of 20-30% at 5 years are consistent across large series, driven by rod fracture, PJK and pseudarthrosis.
- Age-adjusted alignment is now standard practice: older patients are deliberately left in mild positive sagittal balance to reduce proximal junctional failure.
High- vs Limited-Resource Variation
- High-resource settings: Routine standing full-length EOS or stitched radiography, intraoperative neuromonitoring (SSEP/MEP/EMG), cell salvage, tranexamic acid, and dedicated spinal rehabilitation units.
- Limited-resource settings: Reliance on long-cassette plain films, selective neuromonitoring, and staged or lower-risk osteotomy choices; PSO/VCR may be deferred or referred to deformity centres given blood-loss and monitoring requirements.
Perioperative Optimisation (Globally Applicable)
- Bone health: DEXA, treat osteoporosis (e.g. teriparatide, antiresorptives) before major instrumented correction.
- Antifibrinolytics (tranexamic acid) and cell salvage to manage 1-3 litre blood loss in PSO.
- Mandatory intraoperative neuromonitoring for all three-column osteotomies.
- Nutritional and cardiopulmonary optimisation; smoking cessation to reduce pseudarthrosis.
Perioperative Protocols (Global Standard)
Infection Prophylaxis
- Cefazolin 2g IV at induction (3g if over 120kg), re-dosed every 3-4 hours intraoperatively; vancomycin 15mg/kg if beta-lactam allergy.
- Intrawound vancomycin powder is widely used to reduce deep surgical site infection in instrumented deformity surgery.
- Continue systemic prophylaxis for no more than 24 hours postoperatively.
Venous Thromboembolism Prophylaxis
- Mechanical prophylaxis (sequential compression devices) intraoperatively and until mobile.
- Chemical prophylaxis (e.g. low-molecular-weight heparin) typically started 24-48 hours postoperatively once epidural haematoma risk is acceptable, balancing bleeding against thromboembolic risk.
- Early mobilisation is the single most effective measure.
Blood and Bone Management
- Tranexamic acid and cell salvage to manage 1-3 litre blood loss in PSO (3-5 litres in VCR).
- Bone morphogenetic protein and autograft/allograft at the osteotomy and fusion bed; optimise osteoporosis preoperatively.
This topic provides comprehensive coverage of flatback syndrome pathophysiology, radiographic assessment (SVA, PI-LL mismatch), conservative management, and surgical correction with Smith-Petersen, PSO, and VCR osteotomies for global fellowship examination preparation.
MCQ Practice Points
Q: What is flatback syndrome and what are its causes?
A: Flatback syndrome: Loss of normal lumbar lordosis causing positive sagittal balance (sagittal vertical axis greater than 5cm anterior to S1). Patients lean forward and cannot stand upright without hip/knee flexion. Causes: (1) Iatrogenic - distraction instrumentation (Harrington rods), hypolordotic fusion constructs; (2) Degenerative disc disease with disc height loss; (3) Vertebral fractures; (4) Ankylosing spondylitis; (5) Adjacent segment degeneration after fusion.
Q: What are the clinical features and compensatory mechanisms in flatback syndrome?
A: Symptoms: Back pain (fatigue), inability to stand erect, forward stooped posture, need to lean on objects. Compensatory mechanisms (from spine distally): Thoracic hyperkyphosis; Hip hyperextension; Knee flexion; Ankle dorsiflexion. With exhaustion, compensatory mechanisms fail and patient leans progressively forward. Physical exam: Forward trunk inclination; Positive sagittal balance; Hip flexion contractures may develop; Diminished lumbar lordosis or frank kyphosis.
Q: How do you assess sagittal balance radiographically?
A: Standing full-spine radiographs essential. Key measurements: SVA (sagittal vertical axis): C7 plumb line to posterior S1 - normal less than 5cm, positive values indicate anterior shift. Pelvic incidence (PI): Fixed anatomic value. Lumbar lordosis (LL): Should approximately equal PI ± 10°. Pelvic tilt (PT): Increases with compensation (pelvis retroversion). T1 pelvic angle: Global sagittal alignment measure. Goal is to restore PI-LL match and normalize SVA.
Q: What are the surgical options for correcting flatback syndrome?
A: Osteotomy techniques (increasing correction): Smith-Petersen osteotomy (SPO): Posterior column shortening through facets, 10° per level. Pedicle subtraction osteotomy (PSO): Wedge resection through all three columns, 30-35° correction per level. Vertebral column resection (VCR): Complete removal of vertebral segment, greatest correction but highest risk. Extension of fusion: Address adjacent segment disease. Selection based on magnitude of deformity and prior fusion status. Often multiple osteotomies required.
Q: What are the complications specific to flatback correction surgery?
A: Neurological injury: Especially with PSO/VCR - cord monitoring essential; Root injury from nerve stretch or direct trauma. Pseudarthrosis: High mechanical load at osteotomy site. Hardware failure: Rod fracture at osteotomy site (stress riser). Proximal junctional kyphosis: Failure above fusion construct. Adjacent segment disease: Increased stress at adjacent levels. Medical complications: High blood loss, prolonged surgery, age-related comorbidities. Mortality rates 1-5% in revision deformity surgery.
At a Glance
- Key Information
- Loss of lumbar lordosis causing sagittal imbalance
- Key Information
- Iatrogenic (Harrington rods, long fusion)
- Key Information
- Forward trunk lean, cannot stand upright
- Key Information
- SVA (C7 plumb to S1) - normal under 5cm
- Key Information
- Under 10 degrees mismatch
- Key Information
- Standing full-length lateral spine X-ray
- Key Information
- Pedicle Subtraction Osteotomy (PSO)
- Key Information
- 25-30 degrees lordosis per level
- Key Information
- 10-30% with PSO/VCR
FLATBACKFlatback Syndrome Features
Hook:The spine is FLAT in the BACK!
SVA-PILLRadiographic Parameters
Hook:Take a PILL to measure SVA!
SPVOsteotomy Options
Hook:SPecial Vertebral procedures - ascending power!
Exam Viva Scenarios
Practise clinical reasoning and management decisions out loud
“A 62-year-old woman presents with severe back pain and forward trunk lean. She had scoliosis surgery with Harrington rods 30 years ago. She can only stand upright for 10 minutes and requires a walker. Full-length standing lateral radiograph shows SVA of 14cm, PI of 58 degrees, LL of 25 degrees, and PT of 32 degrees.”
“A 68-year-old man with no prior spine surgery presents with progressive forward lean over 5 years. He has severe back and leg fatigue with standing and walking. Standing lateral shows SVA 8cm, PI 62 degrees, LL 38 degrees, PT 28 degrees. Multiple disc collapse L2-5. How would you manage this?”
“You are performing a PSO at L3 for flatback correction. After closing the osteotomy, the neurophysiologist reports loss of motor evoked potentials in bilateral lower extremities. What do you do?”
Key Definitions
- Flatback = loss of lumbar lordosis causing sagittal imbalance (forward trunk lean)
- SVA = C7 plumb to posterosuperior S1; normal under 5cm, severe over 10cm
- PI-LL mismatch = Pelvic Incidence minus Lumbar Lordosis; normal under 10 degrees
- Pelvic compensation = posterior pelvic tilt to restore balance (PT normal 10-25 degrees)
Radiographic Parameters
- SVA (Sagittal Vertical Axis): Normal under 5cm, symptoms over 5cm, severe over 10cm
- PI (Pelvic Incidence): FIXED anatomic (35-80 degrees), does NOT change
- LL (Lumbar Lordosis): VARIABLE (40-60 degrees L1-S1), should approximate PI
- PT (Pelvic Tilt): VARIABLE compensation (10-25 degrees), over 25 = exhausted
- PI = PT + SS (sacral slope) - use to check measurement accuracy
Etiologies
- Iatrogenic (most common): Harrington rods, flat fusion, long fusion to sacrum
- Degenerative: Disc collapse, compression fractures, ankylosing spondylitis
- Post-laminectomy: Extensive posterior element removal causing kyphosis
- Traumatic: Vertebral compression fractures, pelvic malunion
Clinical Presentation
- Forward trunk lean with inability to stand upright (cardinal finding)
- Compensatory mechanisms: knee flexion, hip extension, pelvic retroversion
- Severe back and leg fatigue (paraspinals, hip flexors, quadriceps)
- ODI and SF-36 correlate with SVA (worse disability with higher SVA)
- Standing tolerance often under 15-30 minutes
Imaging Requirements
- Standing full-length lateral spine (skull to femoral heads) - MUST be standing
- Arms positioned: fists on clavicles or grasping horizontal bars
- Measure SVA, PI, PT, SS, LL (all on same standing lateral film)
- CT for surgical planning (bony anatomy, pedicle size, prior fusion)
- MRI if radiculopathy or stenosis (neural compression assessment)
Surgical Goals
- Radiographic: SVA under 5cm (ideally 0-3cm), PI-LL under 10 degrees
- Clinical: Upright posture without compensation, reduce pain/disability
- Restore lumbar lordosis to approximately match pelvic incidence
- Avoid complications: neurologic injury, rod fracture, PJK
Osteotomy Options
- SPO (Smith-Petersen): Posterior column only, approximately 10 degrees/level, needs mobile disc
- PSO (Pedicle Subtraction): 3-column, 30 degrees/level, workhorse for flatback
- VCR (Vertebral Column Resection): Complete vertebrectomy, 40 degrees/level, severe cases
- PSO at L3 most common (large body, safer than L4-5, good lordosis contribution)
PSO Technique Key Points
- Instrumentation 3-4 levels above/below, temporary rods for stability
- Laminectomy, pedicle removal, posterior body wedge (30-40 degrees)
- Close osteotomy SLOWLY (1-2mm increments, check neuromonitoring)
- Cantilever closure technique, neural elements shorten (accordion)
- BMP at osteotomy site, decorticate fusion bed, rigid fixation
Complications and Rates
- Neurologic injury: 10-30% (motor 5-10%, sensory 15-25%), 50% resolve by 1 year
- Rod fracture: 10-20% (higher if SVA over 5cm postop, undercorrection)
- PJK (Proximal Junctional Kyphosis): 20-40% (extend to upper thoracic to prevent)
- Pseudarthrosis: 10-20% at osteotomy site (smoking, infection, rod fracture)
- Vascular injury: 1-3% (aorta, vena cava - L4-5 PSO higher risk)
- Infection: 5-10% (deep 3-5%), bleeding: 1-3 liters average PSO
Outcomes
- Patient satisfaction: 70-80% satisfied at 2 years if adequate correction
- ODI improvement: 40-60% reduction (from 50 preop to 25 postop average)
- SVA correction: Average 8-10cm improvement (from 14cm to 4cm)
- Revision rate: 20-30% at 5 years (rod fracture, PJK, pseudarthrosis)
- Correlation: SVA under 5cm postop = best outcomes, over 5cm = rod fracture risk
Exam Pearls
- SVA is KING: Most important outcome predictor (correlates with ODI, SF-36)
- PI-LL target: Under 10 degrees mismatch (predicts rod fracture if over 10)
- PSO at L3: Most common level (large body, safer, good lordosis)
- Neurologic loss during closure: STOP, open osteotomy, optimize perfusion
- Rod fracture = undercorrection: Usually means SVA over 5cm or pseudarthrosis
Outcomes and Evidence
Patient-Reported Outcomes
Improvement Rates:
- Preoperative
- 40-60 (severe disability)
- 2-Year Postoperative
- 20-30 (moderate)
- Improvement
- 40-60% improvement
- Preoperative
- 25-35
- 2-Year Postoperative
- 45-55
- Improvement
- Significant improvement
- Preoperative
- 7-8/10
- 2-Year Postoperative
- 3-4/10
- Improvement
- 50% reduction
- Preoperative
- 5-6/10
- 2-Year Postoperative
- 2-3/10
- Improvement
- 50% reduction
Patient Satisfaction:
- 70-80% satisfied or very satisfied
- 10-20% satisfied with reservations
- 5-10% dissatisfied
Radiographic Outcomes
SVA Correction:
- Postoperative SVA
- 3-5cm (average)
- Correction Achieved
- 8-10cm improvement
- Postoperative SVA
- Achieved in 70-80%
- Correction Achieved
- Correlates with satisfaction
PI-LL Correction:
- Postoperative PI-LL
- 5-15 degrees (average)
- Correction
- 20-25 degrees improvement
- Postoperative PI-LL
- Achieved in 60-70%
- Correction
- Correlates with rod fracture risk
Schwab et al. (2010) - Spinopelvic Realignment Targets
- Current concepts review establishing surgical realignment objectives for adult spinal deformity
- Restoring low sagittal vertical axis and pelvic tilt identified as critical surgical goals
- Lumbar lordosis must be proportional to pelvic incidence (PI-LL match)
- Emphasises global alignment and individualised, proportional targets over single thresholds
Smith et al. (2012) - Symptomatic Rod Fracture After Deformity Fusion
- Multicentre retrospective review of 442 adult deformity patients with long posterior fusion
- Symptomatic rod fracture in 6.8% overall but 15.8% after pedicle subtraction osteotomy (PSO)
- Among PSO rod fractures, 89% occurred at or adjacent to the PSO site
- Postoperative sagittal malalignment (SVA over 50mm) increased rod fracture risk; cobalt chromium rods fractured less than titanium or stainless steel
Bridwell et al. (2009) - Operative vs Nonoperative Treatment of Adult Deformity
- Prospective multicentre study of 160 adult symptomatic lumbar scoliosis patients (ages 40-80)
- Operative cohort improved significantly across all QOL measures (SRS, ODI, pain scores) at 2 years
- Nonoperative cohort showed no improvement, with frequent nonsignificant decline
- Limited by only 45% follow-up in the nonoperative group versus 95% operative
Lagrone et al. (1988) - Landmark Description of Flatback After Fusion
- 55 patients with symptomatic loss of lumbar lordosis after spinal fusion treated with corrective osteotomy
- 95% could not stand erect and 89% had back pain at presentation
- Distraction instrumentation with a hook in the lower lumbar spine or sacrum was the most frequent contributing factor
- Failure to restore sagittal balance led to higher pseudarthrosis and recurrent deformity; complications in 60%
Bridwell et al. (2003) - Pedicle Subtraction Osteotomy for Fixed Sagittal Imbalance
- 27 consecutive patients with fixed sagittal imbalance treated by lumbar pedicle subtraction osteotomy
- Average lordosis increase of 34.1 degrees achieved through a single posterior osteotomy
- Average C7 sagittal plumb line improvement of 13.5cm
- Significant improvement in Oswestry and pain scores; pseudarthrosis and breakdown caudal to fusion were the main failure modes
Glassman et al. (2005) - Sagittal Balance Predicts Symptoms
- 298 adult deformity patients (172 unoperated, 126 with prior fusion) studied on standing radiographs
- Positive sagittal balance was the most reliable radiographic predictor of pain and function in both groups
- Magnitude of coronal deformity and coronal correction were less critical parameters
- Restoration of normal sagittal balance is the key goal of reconstructive spine surgery
Complication Rates (Pooled Series)
- Incidence
- 10-30%
- Severity
- 50% resolve by 1 year
- Incidence
- 5-10%
- Severity
- Motor deficit most concerning
- Incidence
- 10-20%
- Severity
- Higher if SVA over 5cm postop
- Incidence
- 20-40%
- Severity
- 10-15% require revision
- Incidence
- 10-20%
- Severity
- 5-10% require revision
- Incidence
- 5-10%
- Severity
- Deep infection 3-5%
- Incidence
- 20-30%
- Severity
- At 2-5 years
Factors Predicting Outcomes
Good Outcome Predictors:
- Postoperative SVA under 5cm
- PI-LL mismatch under 10 degrees
- Solid fusion at 1 year
- No neurologic complications
Poor Outcome Predictors:
- Undercorrection (SVA over 5cm)
- Rod fracture
- Proximal junctional kyphosis
- Neurologic injury
- Infection
References
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Schwab F, Patel A, Ungar B, et al. Adult spinal deformity-postoperative standing imbalance: how much can you tolerate? An overview of key parameters in assessing alignment and planning corrective surgery. Spine. 2010;35(25):2224-31.
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Smith JS, Shaffrey CI, Ames CP, et al. Assessment of symptomatic rod fracture after posterior instrumented fusion for adult spinal deformity. Neurosurgery. 2012;71(4):862-7.
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Bridwell KH, Glassman S, Horton W, et al. Does treatment (nonoperative and operative) improve the two-year quality of life in patients with adult symptomatic lumbar scoliosis: a prospective multicenter evidence-based medicine study. Spine. 2009;34(20):2171-8.
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Glassman SD, Berven S, Bridwell K, et al. Correlation of radiographic parameters and clinical symptoms in adult scoliosis. Spine. 2005;30(6):682-8.
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Bridwell KH, Lewis SJ, Lenke LG, et al. Pedicle subtraction osteotomy for the treatment of fixed sagittal imbalance. J Bone Joint Surg Am. 2003;85(3):454-63.
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Kim YJ, Bridwell KH, Lenke LG, et al. Proximal junctional kyphosis in adult spinal deformity after segmental posterior spinal instrumentation and fusion: minimum five-year follow-up. Spine. 2008;33(20):2179-84.
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Yagi M, Akilah KB, Boachie-Adjei O. Incidence, risk factors and classification of proximal junctional kyphosis: surgical outcomes review of adult idiopathic scoliosis. Spine. 2011;36(1):E60-8.
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Smith JS, Klineberg E, Schwab F, et al. Change in classification grade by the SRS-Schwab Adult Spinal Deformity Classification predicts impact on health-related quality of life measures: prospective analysis of operative and nonoperative treatment. Spine. 2013;38(19):1663-71.
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Schwab FJ, Blondel B, Bess S, et al. Radiographical spinopelvic parameters and disability in the setting of adult spinal deformity: a prospective multicenter analysis. Spine. 2013;38(13):E803-12.
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Kim HJ, Bridwell KH, Lenke LG, et al. Patients with proximal junctional kyphosis requiring revision surgery have higher postoperative lumbar lordosis and larger sagittal balance corrections. Spine. 2014;39(9):E576-80.
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Cho KJ, Bridwell KH, Lenke LG, et al. Comparison of Smith-Petersen versus pedicle subtraction osteotomy for the correction of fixed sagittal imbalance. Spine. 2005;30(18):2030-7.
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Yang BP, Ondra SL, Chen LA, et al. Clinical and radiographic outcomes of thoracic and lumbar pedicle subtraction osteotomy for fixed sagittal imbalance. J Neurosurg Spine. 2006;5(1):9-17.
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Auerbach JD, Lenke LG, Bridwell KH, et al. Major complications and comparison between 3-column osteotomy techniques in 105 consecutive spinal deformity procedures. Spine. 2012;37(14):1198-210.
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Ames CP, Smith JS, Scheer JK, et al. Impact of spinopelvic alignment on decision making in deformity surgery in adults: A review. J Neurosurg Spine. 2012;16(6):547-64.
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Lafage V, Schwab F, Patel A, et al. Pelvic tilt and truncal inclination: two key radiographic parameters in the setting of adults with spinal deformity. Spine. 2009;34(17):E599-606.