Is an ossified posterior longitudinal ligament (OPLL) considered unstable?

Ossification of the Posterior Longitudinal Ligament (OPLL): Stability Assessment

Ossification of the posterior longitudinal ligament (OPLL) itself is not considered inherently unstable, but it can lead to progressive spinal canal narrowing and neurological deterioration without necessarily causing mechanical instability.

Pathophysiology and Stability Considerations

OPLL is characterized by heterotopic ossification of the posterior longitudinal ligament that can result in:

• Progressive narrowing of the spinal canal 1
• Potential compression of the spinal cord and nerve roots 1
• Most commonly affects the cervical spine (3.2% prevalence) compared to thoracic spine (0.8%) 1
• Higher prevalence in Asian populations (4.6% in Korean population vs 1.7% in white US population) 1

Stability Assessment

OPLL itself typically does not cause mechanical instability of the spine for several reasons:

1. The ossification process actually creates additional structural support along the posterior aspect of the vertebral bodies
2. The condition represents a hyperostotic state rather than a destabilizing process 2
3. The primary clinical concern is neurological compromise from spinal canal stenosis, not instability 1

Diagnostic Evaluation

Imaging Modalities for OPLL

• CT scan: Gold standard for OPLL diagnosis with 94-100% sensitivity 3

  • Superior for identifying OPLL type, thickness, and extent 1
  • Best for evaluating neuroforaminal and spinal canal narrowing 1

• Plain radiographs: Limited sensitivity (49-82%) 3

  • May serve as initial screening tool 1
  • Less reliable for definitive diagnosis 1

• MRI: Limited sensitivity (32-44.3%) for OPLL detection 1

  • Primary value is in assessing cord compression and signal changes 1
  • Better for evaluating soft tissue and neural structures 3

Clinical Implications of Imaging

• CT myelography in flexion and extension can identify position-dependent cord compression in cervical spinal stenosis from OPLL 1
• Signal changes on T2-weighted MRI correlate with worse neurological outcomes 4
• Higher mass occupying ratio of OPLL correlates with worse clinical scores 4

Management Considerations

Conservative Management

• Appropriate for asymptomatic patients or those with mild symptoms 5
• Includes physical therapy, NSAIDs, and activity modification 3
• Close monitoring is essential as OPLL can progress over time 6

Surgical Indications

Surgical intervention should be considered for:

1. Progressive neurological deficits
2. Myelopathy or severe radiculopathy
3. Evidence of significant cord compression

Surgical Approach Selection

• Anterior approach: Showed 58% neurological improvement rate 4

  • Preferred for focal OPLL causing significant anterior compression
  • Directly addresses the compressive pathology

• Posterior approach: Showed 31% neurological improvement rate 4

  • Laminectomy with fusion is recommended over laminectomy alone 1
  • Prevents late deformity compared to laminectomy without fusion 1

Important Considerations and Pitfalls

1. Progression risk: OPLL can continue to grow even after posterior decompression surgery 6

   • Long-term studies show both longitudinal and transverse disease progression in patients treated surgically and conservatively 6

2. Dural penetration: The presence of dural penetration by OPLL correlates with OPLL subtype and increases surgical risk 4

3. Delayed neurological deterioration: Despite radiographic progression, the rate of neurological decline after laminoplasty is relatively low 6

4. Surgical complications: Risk of C5 nerve root injury during decompressive procedures 1

5. Monitoring considerations: Intraoperative neurophysiological monitoring is recommended during surgery for OPLL to detect potential iatrogenic injury 1

Conclusion

OPLL represents a progressive ossification process that can cause neurological compromise through spinal canal stenosis, but it does not typically cause mechanical instability of the spine. The primary clinical concern is neurological deterioration from cord compression rather than instability. Appropriate imaging with CT and MRI is essential for diagnosis and surgical planning, with surgical intervention indicated for progressive neurological deficits or significant cord compression.