Flatback Syndrome

High-yield overview

Loss of lumbar lordosis causing forward trunk lean with inability to stand upright

5cmSVA threshold for symptoms

10°PI-LL mismatch threshold

30°PSO correction per level

80%Patient satisfaction post-correction

Osteotomy Types

SPO

PatternSmith-Petersen (posterior only)

Treatment10 degrees per level

PSO

PatternPedicle Subtraction (3-column)

Treatment30 degrees per level

VCR

PatternVertebral Column Resection

Treatment40+ degrees per level

Critical Must-Knows

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)

Clinical Pearls

"
Patients cannot stand upright without compensation (knee flexion, hip extension)
"
ODI and SF-36 correlate with SVA - most important predictor of disability
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Always assess pelvic compensation (pelvic tilt, pelvic incidence-lumbar lordosis)
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Rod fracture risk high if SVA not corrected adequately

High Yield Exam Points

SVA is King

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.

PI-LL Mismatch

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.

Osteotomy Hierarchy

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.

Iatrogenic is Most Common

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.

At a Glance

Aspect	Key Information
Definition	Loss of lumbar lordosis causing sagittal imbalance
Most common cause	Iatrogenic (Harrington rods, long fusion)
Cardinal symptom	Forward trunk lean, cannot stand upright
Key measurement	SVA (C7 plumb to S1) - normal under 5cm
PI-LL target	Under 10 degrees mismatch
Gold standard imaging	Standing full-length lateral spine X-ray
First-line surgical	Pedicle Subtraction Osteotomy (PSO)
PSO correction	25-30 degrees lordosis per level
Neurologic risk	10-30% with PSO/VCR

Mnemonic

FLATBACKFlatback Syndrome Features

F	Forward trunk lean Cannot stand upright, compensatory knee/hip flexion
L	Lordosis loss Lumbar spine flat or kyphotic
A	Anterior imbalance C7 plumb line falls anterior to S1
T	Ten degrees PI-LL Mismatch threshold for surgery (over 10 degrees)
B	Back pain severe Paraspinal fatigue from constant compensation
A	Assessment with SVA Sagittal vertical axis - key measurement
C	Correction with osteotomy PSO (30 degrees), VCR (40 degrees)
K	Knee and hip compensation Flexed knees, extended hips to maintain balance

F	Forward trunk lean Cannot stand upright, compensatory knee/hip flexion	T	Ten degrees PI-LL Mismatch threshold for surgery (over 10 degrees)	C	Correction with osteotomy PSO (30 degrees), VCR (40 degrees)
L	Lordosis loss Lumbar spine flat or kyphotic	B	Back pain severe Paraspinal fatigue from constant compensation	K	Knee and hip compensation Flexed knees, extended hips to maintain balance
A	Anterior imbalance C7 plumb line falls anterior to S1	A	Assessment with SVA Sagittal vertical axis - key measurement

Hook:The spine is FLAT in the BACK!

Mnemonic

SVA-PILLRadiographic Parameters

S	Sagittal Vertical Axis C7 plumb to S1, normal under 5cm
V	Vertical alignment Head over pelvis alignment
A	Anterior displacement Positive SVA = C7 anterior to S1
P	Pelvic Incidence Fixed anatomic parameter (angle from S1 to hip axis)
I	Incidence minus lordosis PI-LL mismatch calculation
L	Lumbar Lordosis Measured L1-S1, should match PI within 10 degrees
L	Less than 10 degrees Target: PI-LL under 10 degrees mismatch

S	Sagittal Vertical Axis C7 plumb to S1, normal under 5cm	P	Pelvic Incidence Fixed anatomic parameter (angle from S1 to hip axis)	L	Less than 10 degrees Target: PI-LL under 10 degrees mismatch
V	Vertical alignment Head over pelvis alignment	I	Incidence minus lordosis PI-LL mismatch calculation
A	Anterior displacement Positive SVA = C7 anterior to S1	L	Lumbar Lordosis Measured L1-S1, should match PI within 10 degrees

Hook:Take a PILL to measure SVA!

Mnemonic

SPVOsteotomy Options

S	Smith-Petersen Osteotomy (SPO) Posterior column only, approximately 10 degrees/level, mobile disc needed
P	Pedicle Subtraction Osteotomy (PSO) 3-column, 30 degrees/level, workhorse for flatback
V	Vertebral Column Resection (VCR) Complete vertebrectomy, 40 degrees, severe deformity

S	Smith-Petersen Osteotomy (SPO) Posterior column only, approximately 10 degrees/level, mobile disc needed
P	Pedicle Subtraction Osteotomy (PSO) 3-column, 30 degrees/level, workhorse for flatback
V	Vertebral Column Resection (VCR) Complete vertebrectomy, 40 degrees, severe deformity

Hook:SPecial Vertebral procedures - ascending power!

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

Parameter	Value
Historic prevalence	20-40% after Harrington rod instrumentation
Current prevalence	5-10% after modern spinal fusion
Peak age	50-70 years (iatrogenic), variable (degenerative)
Gender	Female predominance (2:1) - more fusions for scoliosis

Risk Factors

Category	Specific Factors
Iatrogenic	Harrington rods, long fusion to sacrum, flat rod contouring
Degenerative	Disc collapse, compression fractures, ankylosing spondylitis
Post-surgical	Pseudarthrosis, junctional kyphosis, hardware failure
Patient factors	Osteoporosis, smoking, obesity, prior laminectomy

Historical Context

Clinical Pearl

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)

Parameter	Definition	Normal Range	Clinical Significance
Pelvic Incidence (PI)	Angle from S1 midpoint to hip axis	35-80 degrees	FIXED anatomic parameter (cannot change)
Pelvic Tilt (PT)	Vertical to S1-hip axis line	10-25 degrees	VARIABLE - increases with compensation
Sacral Slope (SS)	S1 endplate to horizontal	30-50 degrees	VARIABLE - decreases in flatback
PI = PT + SS	Mathematical relationship	Always true	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.

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

Location	Mechanism	Characteristics
Paraspinal muscles	Constant isometric contraction	Burning, aching, fatigue
Thighs (anterior)	Hip extension compensation	Cramping, tightness
Knees	Flexion compensation	Aching, early arthritis
Buttocks	Gluteal fatigue	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

Finding	Significance
Forward trunk lean	Cannot stand upright without support
Knee flexion	Compensatory mechanism
Hip extension	Limited by tight hip flexors
Gait	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

Flatback Special Tests

Test	Technique	Positive Finding
Sagittal balance test	Patient flexes forward, attempts to stand upright	Cannot achieve upright position without knee flexion
Wall test	Patient stands with back to wall, attempts to touch wall with back of head	Head far anterior to wall (over 15cm abnormal)
Scoliosis forward bend test	Patient bends forward from waist	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

SVA	Disability Level
Under 5cm	Minimal disability
5-10cm	Moderate disability
Over 10cm	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)

Measurement	Technique	Normal	Abnormal
SVA	Plumb line from C7 vertebral body center to posterosuperior S1	Under 5cm	Over 5cm
Interpretation	Positive = C7 anterior to S1 (flatback)	0-5cm	Over 10cm = severe

Pelvic Parameters

Parameter	Measurement	Normal	Flatback
Pelvic Incidence (PI)	Angle: S1 midpoint to hip axis, perpendicular to S1	35-80 degrees	FIXED (anatomic)
Pelvic Tilt (PT)	Angle: vertical to line from S1 to hip axis	10-25 degrees	Over 25 degrees (compensated)
Sacral Slope (SS)	Angle: S1 endplate to horizontal	30-50 degrees	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

Clinical Pearl

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:

Type	SVA	PT	Interpretation
Type 0	Under 5cm	Under 25 degrees	Compensated, minimal symptoms
Type I	5-10cm	Under 25 degrees	Mild imbalance
Type II	Over 10cm	Under 25 degrees	Severe imbalance, compensation failing
Type III	Any	Over 25 degrees	Severe, pelvic compensation exhausted

Surgical Implications:

Type 0: Conservative management
Type I: Consider surgery if symptomatic
Type II-III: Surgery usually indicated

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:

Exercise Type	Examples	Benefit
Core strengthening	Planks, bridges, dead bugs	Improve paraspinal endurance
Hip flexor stretching	Thomas stretch, kneeling lunge	Reduce compensatory hip extension
Hamstring stretching	Seated hamstring stretch	Allow pelvic rotation
Postural training	Wall slides, chin tucks	Awareness and positioning

Limitations: Cannot restore lost lordosis or correct fixed deformity.

Medications

Class	Examples	Use	Limitations
NSAIDs	Ibuprofen, naproxen	Muscle inflammation, pain	GI side effects, limited efficacy
Muscle relaxants	Cyclobenzaprine	Paraspinal spasm	Sedation, not for long-term
Neuropathic agents	Gabapentin, pregabalin	If radicular component	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

Device	Use	Limitation
Walker with forearm supports	Unloads spine, allows forward lean	Dependence, social stigma
Cane	Minimal support	Insufficient for severe flatback
Corset/brace	May reduce pain	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:

Parameter	Assessment	Surgical Plan
SVA	5-10cm	Single-level PSO may suffice
SVA	Over 10cm	May need 2-level PSO or PSO + SPO
PI-LL	20-30 degrees	Single-level PSO (30 degrees correction)
PI-LL	Over 40 degrees	Consider VCR or 2-level PSO
Prior fusion	Solid fusion mass	Osteotomy through fusion or adjacent
Osteoporosis	DEXA T-score under -2.5	Optimize bone health, consider cement augmentation

Osteotomy Level Selection:

Level	Advantages	Disadvantages
L2	Large vertebral body, high lordosis potential	High in lumbar spine, junctional stress
L3	Most common PSO level, large body, safer	Moderate lordosis contribution
L4	Good lordosis, mid-lumbar	Smaller body, L5 root at risk
L5	Maximum lordosis potential	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

Type	Incidence	Mechanism	Management
Motor deficit	5-10%	Direct injury, ischemia, hematoma	Stop closure, release compression, imaging
Sensory deficit	15-25%	Nerve root traction	Often transient, monitor
Cauda equina	1-2%	Severe canal compromise	Immediate decompression

Vascular Injury

Vessel	Incidence	Risk Factors	Management
Aorta	0.5-1%	PSO at L4-5, osteoporotic collapse	Vascular surgery consult, open repair
Vena cava	0.5-1%	Anterior perforation	Direct repair, difficult access
Lumbar arteries	5-10%	Lateral dissection	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

Complication	Incidence	Risk Factors	Prevention
PE/DVT	5-10%	Long surgery, immobility	Chemoprophylaxis, SCDs
Pneumonia	5-8%	Prolonged intubation, pain	Early mobilization, incentive spirometry
Ileus	10-20%	Bowel retraction, narcotics	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)

Feature	Details
Incidence	20-40% after PSO
Definition	Kyphosis over 10 degrees at upper instrumented vertebra (UIV)
Risk factors	Stopping at thoracolumbar junction, osteoporosis, overcorrection
Prevention	Extend to upper thoracic spine (T9-T10), avoid overcorrection
Treatment	Extension of fusion if symptomatic or progressive

Rod Fracture

Parameter	Details
Incidence	10-20% overall (higher if SVA over 5cm postop)
Timing	6 months to 2 years
Risk factors	Undercorrection (SVA over 5cm), pseudarthrosis, single rods
Prevention	Adequate SVA correction, dual rods, solid fusion
Treatment	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

Complication Prevention

Complication	Prevention Strategy
Neurologic injury	Slow closure, neuromonitoring, adequate decompression, avoid overstretching
Vascular injury	Careful anterior dissection, stay midline, palpate aorta
Rod fracture	Adequate SVA correction (under 5cm), dual rods, solid fusion
PJK	Extend to upper thoracic, avoid overcorrection, prophylactic vertebroplasty UIV
Infection	Prophylactic antibiotics, meticulous hemostasis, vancomycin powder
Pseudarthrosis	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:

Timepoint	Assessment	Imaging
2 weeks	Wound check, suture removal	None (unless concern)
6 weeks	Clinical exam, pain assessment	AP/Lateral X-rays (standing)
3 months	Neurologic exam, function	AP/Lateral X-rays (standing)
6 months	Function, return to activities	AP/Lateral X-rays
1 year	Final assessment	AP/Lateral X-rays, CT if concern for fusion
2 years	Long-term outcome	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

Activity	Restriction Period	Rationale
Lifting	No lifting over 10 lbs for 3 months	Protect fusion, prevent hardware failure
Driving	No driving for 6 weeks (narcotics)	Safety, pain control
Return to work (desk)	3 months	Depends on pain, function
Return to work (manual)	6-12 months	Heavy labor risk to fusion
Sports	Light activities 6 months, full 1 year	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.

Outcomes and Evidence

Patient-Reported Outcomes

Improvement Rates:

Outcome Measure	Preoperative	2-Year Postoperative	Improvement
ODI	40-60 (severe disability)	20-30 (moderate)	40-60% improvement
SF-36 Physical	25-35	45-55	Significant improvement
Back pain VAS	7-8/10	3-4/10	50% reduction
Leg pain VAS	5-6/10	2-3/10	50% reduction

Patient Satisfaction:

70-80% satisfied or very satisfied
10-20% satisfied with reservations
5-10% dissatisfied

Radiographic Outcomes

SVA Correction:

Preoperative SVA	Postoperative SVA	Correction Achieved
12-15cm (average)	3-5cm (average)	8-10cm improvement
Target: Under 5cm	Achieved in 70-80%	Correlates with satisfaction

PI-LL Correction:

Preoperative PI-LL	Postoperative PI-LL	Correction
25-35 degrees (average)	5-15 degrees (average)	20-25 degrees improvement
Target: Under 10 degrees	Achieved in 60-70%	Correlates with rod fracture risk

Schwab et al. (2010) - Spinopelvic Realignment Targets

Schwab F, Patel A, Ungar B, et al. • Spine (2010)

Key Findings:

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

Clinical Implication: Provides the framework for individualised SVA, PT and PI-LL realignment targets used in flatback correction planning.

Verify on PubMed (PMID 21102297)

Smith et al. (2012) - Symptomatic Rod Fracture After Deformity Fusion

III

Smith JS, Shaffrey CI, Ames CP, et al. • Neurosurgery (2012)

Key Findings:

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

Clinical Implication: Demonstrates why adequate SVA correction and rod material/configuration matter at the osteotomy site to reduce rod fracture.

Verify on PubMed (PMID 22989960)

Bridwell et al. (2009) - Operative vs Nonoperative Treatment of Adult Deformity

Bridwell KH, Glassman S, Horton W, et al. • Spine (2009)

Key Findings:

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

Clinical Implication: Supports surgical correction over conservative care for symptomatic adult deformity once a conservative trial has failed.

Verify on PubMed (PMID 19752703)

Lagrone et al. (1988) - Landmark Description of Flatback After Fusion

Lagrone MO, Bradford DS, Moe JH, et al. • J Bone Joint Surg Am (1988)

Key Findings:

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%

Clinical Implication: Foundational paper defining flatback as an iatrogenic deformity and establishing prevention through avoiding lower-lumbar distraction instrumentation.

Verify on PubMed (PMID 3356724)

Bridwell et al. (2003) - Pedicle Subtraction Osteotomy for Fixed Sagittal Imbalance

Bridwell KH, Lewis SJ, Lenke LG, et al. • J Bone Joint Surg Am (2003)

Key Findings:

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

Clinical Implication: Landmark series quantifying the correction power of single-level PSO (roughly 30 degrees) that underpins modern flatback surgical planning.

Verify on PubMed (PMID 12637431)

Glassman et al. (2005) - Sagittal Balance Predicts Symptoms

III

Glassman SD, Berven S, Bridwell K, et al. • Spine (2005)

Key Findings:

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

Clinical Implication: Establishes sagittal vertical axis as the dominant outcome-determining parameter, prioritising sagittal over coronal correction in flatback surgery.

Verify on PubMed (PMID 15770185)

Complication Rates (Pooled Series)

Complication	Incidence	Severity
Neurologic (any)	10-30%	50% resolve by 1 year
Neurologic (permanent)	5-10%	Motor deficit most concerning
Rod fracture	10-20%	Higher if SVA over 5cm postop
PJK	20-40%	10-15% require revision
Pseudarthrosis	10-20%	5-10% require revision
Infection	5-10%	Deep infection 3-5%
Reoperation (any reason)	20-30%	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

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.
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.
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.
Glassman SD, Berven S, Bridwell K, et al. Correlation of radiographic parameters and clinical symptoms in adult scoliosis. Spine. 2005;30(6):682-8.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.

Exam Viva Scenarios

Use these scenarios to practise clinical reasoning and management decisions

CLINICAL SCENARIOModerate

Scenario 1: Flatback After Harrington Rod

CLINICAL PROMPT

"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."

PRACTICAL APPROACH

This is classic iatrogenic flatback syndrome from distraction instrumentation. I would take a systematic approach: First, confirm the diagnosis with clinical assessment (forward trunk lean, compensatory mechanisms) and radiographic parameters (SVA 14cm - severely abnormal, PI-LL mismatch 33 degrees - severe). Second, assess compensatory mechanisms (pelvic tilt 32 degrees - compensation exhausted). Third, attempt conservative management for 3-6 months (physiotherapy, medications, assistive devices). If conservative fails, I would counsel for surgical correction with pedicle subtraction osteotomy. Goal: restore SVA to under 5cm and PI-LL to under 10 degrees. I would discuss risks including neurologic injury (10-30%), rod fracture (10-20%), and need for long fusion. Expected improvement is 70-80% patient satisfaction if adequate correction achieved.

KEY CLINICAL POINTS

Recognize iatrogenic flatback from Harrington rods (distraction without lordosis)

Calculate PI-LL mismatch: 58 - 25 = 33 degrees (severe, requires 30-degree correction)

Assess pelvic compensation: PT 32 degrees (exhausted, no reserve)

Surgical goal: SVA under 5cm, PI-LL under 10 degrees

PSO at L3 would correct ~30 degrees, achieve target LL of 55-60 degrees

COMMON PITFALLS

Jumping to surgery without conservative trial (need 3-6 months)

Undercorrecting (leaving SVA over 5cm leads to rod fracture)

Not explaining compensation (examiners want to hear about pelvic tilt, hip/knee)

Forgetting to mention proximal junctional kyphosis risk (20-40%)

FURTHER QUESTIONS

"What level would you choose for PSO? (L3 most common - large body, safer)"

"What if she has osteoporosis? (Optimize bone health, consider cement augmentation, extend fusion)"

"What is your target lumbar lordosis? (Should match PI - target 55-60 degrees)"

"How do you prevent rod fracture? (Adequate correction SVA under 5cm, dual rods, solid fusion)"

CLINICAL SCENARIOModerate

Scenario 2: Degenerative Flatback

CLINICAL PROMPT

"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?"

PRACTICAL APPROACH

This is degenerative flatback syndrome with moderate sagittal imbalance. I would assess: First, the deformity severity (SVA 8cm - moderate, PI-LL mismatch 24 degrees - significant). Second, compensatory mechanisms (PT 28 degrees - some reserve remaining). Third, trial conservative management (physiotherapy, NSAIDs, epidurals for 3-6 months). If he fails conservative and has significant disability (ODI over 40), I would offer surgical correction. Options include Smith-Petersen osteotomies at multiple levels (if discs mobile) or single-level PSO (if fused/stiff). PSO at L3 would give 30 degrees correction, restoring LL to approximately 68 degrees (close to PI of 62). I would discuss risks (neurologic 10-30%, rod fracture, PJK) and expected outcomes (70-80% satisfaction if adequate correction). Would need long fusion T10-pelvis given deformity severity.

KEY CLINICAL POINTS

Degenerative cause: multiple disc collapse causing lordosis loss

PI-LL calculation: 62 - 38 = 24 degrees (requires ~25-30 degree correction)

PT 28 degrees shows some pelvic compensation remaining (not exhausted like Type III)

PSO preferred over multiple SPOs if anterior column stiff (disc collapse)

Target LL approximately 60-70 degrees (within 10 degrees of PI 62)

COMMON PITFALLS

Choosing SPO when anterior column is stiff from disc collapse (will not close)

Not recognizing need for long fusion (deformity requires T10-pelvis)

Undercorrecting (24 degree mismatch needs full 25-30 degree PSO)

Forgetting about adjacent segment risk above short fusion

FURTHER QUESTIONS

"SPO vs PSO - which would you choose? (PSO - anterior column stiff from disc collapse)"

"What if he has vascular claudication too? (Vascular workup, may need vascular surgery first)"

"How do you assess fusion at 1 year? (CT scan for bridging bone, flexion-extension X-rays)"

"What if rod fractures at 18 months? (Assess fusion, SVA, and pseudarthrosis - likely needs revision)"

CLINICAL SCENARIOStandard

Scenario 3: Postoperative Neurologic Deficit

CLINICAL PROMPT

"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?"

PRACTICAL APPROACH

This is a neurologic emergency. I would immediately: First, STOP the procedure and assess the situation. Second, partially open the osteotomy (release closure by 2-3mm) to decompress neural elements. Third, check for technical issues (pedicle screw malposition, hematoma, over-closure). Fourth, optimize spinal cord perfusion (raise blood pressure to MAP 85-90mmHg, ensure adequate hemoglobin). Fifth, if signals do not return, perform imaging (intraoperative CT or fluoroscopy) to assess hardware and canal. If signals partially recover, I would accept less correction and close osteotomy more gradually. If no recovery, consider wake-up test to assess clinical function. Postoperatively, close neurologic monitoring, MRI if deficit persists to rule out hematoma. Document extensively and counsel family. Most deficits are transient from traction or ischemia and improve over weeks to months, but permanent deficit occurs in 5-10% of PSO cases.

KEY CLINICAL POINTS

STOP immediately when neuromonitoring changes occur

Release closure to decompress neural elements (reverse the maneuver)

Check technical factors: screw position, canal, hematoma

Optimize perfusion: MAP 85-90mmHg, hemoglobin over 9-10g/dL

Document meticulously and communicate with patient/family

Most deficits transient (50% resolve), but permanent deficit risk 5-10%

COMMON PITFALLS

Continuing closure hoping signals return (will worsen injury)

Not checking blood pressure (hypotension can cause cord ischemia)

Assuming screw malposition without imaging (may be traction injury)

Forgetting wake-up test option (clinical assessment can guide decision)

Not documenting thoroughly (medicolegal essential)

FURTHER QUESTIONS

"What if signals don't return after opening? (Wake-up test, intraoperative CT, optimize perfusion)"

"What is the natural history of PSO neurologic deficits? (50% resolve by 1 year, 5-10% permanent)"

"How do you prevent this complication? (Slow closure, continuous monitoring, adequate decompression)"

"What would you tell the family postoperatively? (Honest discussion, deficit occurred, monitoring, hopeful but uncertain prognosis)"

MCQ Practice Points

Clinical Pearl

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.

Clinical Pearl

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.

Clinical Pearl

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.

Clinical Pearl

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.

Clinical Pearl

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.

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

Body / Group	Position on Sagittal Realignment
SRS-Schwab (ISSG)	Classification grading by SVA, PT and PI-LL; targets SVA under 4cm, PT under 20-25 degrees, PI-LL under 10 degrees
AO Spine / AOSpine deformity	Endorses age-adjusted alignment targets (older patients tolerate higher SVA/PI-LL); three-column osteotomy for fixed deformity
Scoliosis Research Society	Maintains adult deformity outcome registry; emphasises sagittal over coronal correction (Glassman 2005)
NICE / BOA (UK)	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.