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

Risk Factors

Historical Context

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)

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

Etiologies

📊 Management Algorithm

Click to expand

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:

Limitations: Cannot restore lost lordosis or correct fixed deformity.

Medications

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

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.

Goals of Surgical Correction

Radiographic Goals:

1. SVA under 5cm (ideally 0-3cm)
2. PI-LL mismatch under 10 degrees
3. Restore lumbar lordosis to match pelvic incidence
4. Maintain coronal balance

Clinical Goals:

1. Allow upright posture without compensation
2. Reduce pain and disability
3. Improve walking tolerance and ADLs
4. Minimize complications

Surgical Options Overview

Surgical Planning

Preoperative Assessment:

Osteotomy Level Selection:

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:

1. Exposure: Midline incision, subperiosteal dissection
2. Screw placement: Pedicle screws 3-4 levels above and below osteotomy
3. Temporary rods: Place to maintain stability

Osteotomy Steps:

1. Laminectomy: Complete removal of lamina, spinous process at osteotomy level
2. Facetectomy: Remove inferior and superior facets bilaterally
3. Pedicle resection: Remove pedicles bilaterally (identify nerve roots)
4. Posterior body resection:
   • Remove posterior 1/3 to 1/2 of vertebral body
   • Create 30-40 degree wedge
   • Taper resection laterally (egg-shaped)
5. Nerve root decompression: Mobilize nerve roots, protect during closure

Closure:

1. Remove temporary rods
2. Place final rods (pre-contoured with lordosis)
3. Close osteotomy site SLOWLY:
   • 1-2mm at a time
   • Check neuromonitoring after each increment
   • Use cantilever maneuver
4. Compress instrumentation
5. Decorticate fusion bed
6. 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.

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:

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

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.

Patient-Reported Outcomes

Improvement Rates:

Patient Satisfaction:

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

Radiographic Outcomes

SVA Correction:

PI-LL Correction:

Complication Rates (Meta-Analysis)

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

1. 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.

2. 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.

3. 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.

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

5. 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.

6. 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.

7. 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.

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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

Tertiary Referral: Flatback syndrome surgery is performed at major spine centres with fellowship-trained deformity surgeons. Intraoperative neuromonitoring (SSEPs, MEPs, EMG) is mandatory for osteotomy procedures.

PBS-Subsidised Care: Bone-targeted agents for osteoporosis optimization are PBS-listed. Physiotherapy and pain management are available through Enhanced Primary Care (EPC) plans.

Pre-operative Workup: Bone densitometry (DEXA), nutritional assessment, and cardiopulmonary optimization are standard before major deformity surgery. High-risk patients require multidisciplinary perioperative care.

Rehabilitation: Inpatient rehabilitation following flatback correction is typically 2-4 weeks in dedicated spinal units. Long-term physiotherapy for postural retraining and core strengthening is recommended.

PBS Medications

• Tranexamic acid: Unrestricted for antifibrinolytic therapy during major spine surgery
• Bone morphogenetic protein (BMP): Not PBS-listed; private purchase approximately $3,000-5,000 per kit
• Teriparatide (Forteo): PBS-listed for severe osteoporosis - consider preoperative optimization

Australian Spine Registry Data

• PSO complication rates in Australia: Neurologic 12-18%, rod fracture 15-22%
• Average hospital stay: 7-10 days for PSO
• Revision surgery rate: 25-30% at 5 years
• Patient satisfaction: 75-80% at 2-year follow-up

eTG Recommendations

Antibiotic Prophylaxis:

• Cefazolin 2g IV at induction, then 2g every 4 hours during surgery
• If penicillin allergic: Vancomycin 15-20mg/kg IV
• Continue for 24 hours postoperatively
• Consider vancomycin powder at wound closure

DVT Prophylaxis:

• Enoxaparin 40mg SC daily starting 12-24 hours postoperatively
• Continue for 4-6 weeks (major deformity surgery)
• Sequential compression devices intraoperatively
• Early mobilization critical

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 FRACS examination preparation.