What is pseudoarthrosis of the lumbar spine?

Pseudoarthrosis of the Lumbar Spine: Definition and Management

Pseudoarthrosis of the lumbar spine refers to the failure to achieve solid bony fusion following spinal fusion surgery, typically defined as the absence of osseous fusion by the 1-year post-operative time point. 1 This condition represents a significant complication of lumbar arthrodesis that can lead to persistent pain, disability, and need for revision surgery.

Clinical Presentation and Diagnosis

Patients with lumbar pseudoarthrosis typically present with:

• Recurrent or persistent axial back pain that may worsen with activity
• Pain that improves with rest or recumbency
• Possible radicular symptoms
• Symptoms that develop months to years after the initial fusion surgery

Diagnostic Imaging

The ACR Appropriateness Criteria recommends the following imaging approaches for evaluating pseudoarthrosis 2:

1. CT without IV contrast:

   • Most effective for assessing osseous fusion
   • Can detect hardware failure including prosthetic loosening, malalignment, or metallic fracture
   • Equal to MRI for predicting significant spinal stenosis

2. Flexion-extension radiographs:

   • Useful to evaluate for abnormal motion/increased dynamic mobility
   • Helps detect vertebral body nonunion

3. MRI with and without contrast:

   • Useful when there is concern for infection or soft tissue complications
   • May be limited by metal artifact from hardware

4. SPECT or SPECT/CT:

   • Not recommended as initial imaging
   • May be an adjunct in cases of painful pseudoarthrosis or periprosthetic loosening
   • Can offer diagnostic information when CT or MRI findings are equivocal

5. CT myelography:

   • Useful in patients with significant artifact from metallic surgical hardware on MRI
   • Occasionally more accurate in diagnosing nerve root compression in the lateral recess
   • Disadvantage of requiring lumbar puncture for intrathecal contrast injection

Risk Factors for Pseudoarthrosis

Several factors increase the risk of developing pseudoarthrosis 1, 3:

• Durotomy during surgery (2.2 times increased risk)
• Multi-level fusion (increased risk with more levels)
• Smoking history
• Metabolic disorders
• Inadequate instrumentation
• Poor surgical technique
• Workers' compensation or legal claims

Treatment Options

Treatment of lumbar pseudoarthrosis typically involves revision surgery with the following considerations 1, 4:

1. Surgical approach:

   • Combined anterior and posterior approach has shown higher fusion rates (90%) compared to posterior-only approaches 4
   • Replacing loose instrumentation
   • Use of more rigid fixation systems

2. Biologics:

   • Use of more potent biological agents to enhance fusion
   • Autogenous bone grafting

3. Interbody fusion techniques:

   • ALIF (Anterior Lumbar Interbody Fusion)
   • TLIF (Transforaminal Lumbar Interbody Fusion)
   • PLIF (Posterior Lumbar Interbody Fusion)

4. Alternative techniques:

   • Discoplasty has been reported as a less invasive salvage option for elderly patients with pseudoarthrosis 5

Outcomes and Prognosis

While radiographic fusion rates with revision surgery can be high (up to 90% with combined anteroposterior approach), functional outcomes may be less favorable 4:

• Approximately 35% of patients may still experience functional failure despite solid fusion
• Poor prognostic factors include:
  • Preoperative narcotic use
  • Abnormal neurologic findings before revision surgery
  • Workers' compensation or legal claims

Prevention Strategies

Prevention of pseudoarthrosis includes 1:

• Careful patient selection
• Smoking cessation
• Optimization of metabolic factors
• Use of appropriate instrumentation and biologics
• Meticulous surgical technique
• Adequate fusion length and proper sagittal balance

Key Pitfalls and Caveats

1. The diagnosis of pseudoarthrosis should not be made on imaging alone but correlated with clinical symptoms
2. CT scans are more reliable than plain radiographs for demonstrating fusion status
3. The degree of motion on flexion-extension radiographs that definitively indicates pseudoarthrosis remains controversial
4. Treatment should address not only the pseudoarthrosis but also any adjacent segment disease or hardware failure
5. Careful attention to sagittal balance is essential during revision surgery to prevent adjacent segment degeneration

Pseudoarthrosis remains a challenging complication of spinal fusion surgery that requires careful diagnosis and thoughtful surgical planning to achieve successful outcomes.