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Ossification of the Posterior Longitudinal Ligament (OPLL)

Summary

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  • OPLL is a hyperostotic condition characterised by ectopic ossification of the posterior longitudinal ligament of the spine
  • Most commonly affects the cervical spine, leading to spinal cord compression and myelopathy
  • Diagnosis relies on clinical presentation and imaging findings, with CT and MRI being the modalities of choice1

Pathophysiology

  • Exact aetiology remains unclear, but involves:
    • Genetic factors (e.g. COL6A1, BMP2, and TGF-β1 genes)
    • Metabolic disorders (e.g. diabetes mellitus, obesity)
    • Mechanical stress on the ligament
  • Ossification process:
    • Metaplasia of ligamentous cells to chondrocytes
    • Subsequent endochondral ossification
    • Progressive calcification and bone formation within the ligament

Demographics

  • Prevalence:
    • Higher in East Asian populations (2-4% in Japan)
    • Less common in Western countries (0.1-1.7%)
  • Age of onset:
    • Typically presents in the 5th to 6th decade of life
  • Gender distribution:
    • Male predominance (2:1 to 3:1 male-to-female ratio)

Diagnosis

  • Clinical presentation:
    • Neck pain and stiffness
    • Myelopathy symptoms (e.g. gait disturbance, hand clumsiness)
    • Radiculopathy (less common)
  • Physical examination:
    • Decreased range of motion in the cervical spine
    • Upper motor neuron signs (e.g. hyperreflexia, Hoffman's sign)
    • Sensory deficits in the upper and lower extremities
  • Classification:
    • Continuous type
    • Segmental type
    • Mixed type
    • Localised type (also known as circumscribed type)

Imaging

  • Plain radiographs:
    • Limited sensitivity, especially in early stages
    • May show linear ossification along the posterior aspect of vertebral bodies
  • Computed Tomography (CT):
    • Gold standard for diagnosis and classification
    • Demonstrates extent and morphology of ossification
    • Helps in surgical planning
  • Magnetic Resonance Imaging (MRI):
    • Best for evaluating spinal cord compression and myelopathy
    • T2-weighted images show hypointense signal of ossified ligament
    • Useful for assessing disc herniations and other soft tissue abnormalities

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  • 60-year-old patient with worsening myelopathy affecting the lower limbs.
  • The vertebral canal stenosis was caused by a hypointense/hyperdense ossified posterior longitudinal ligament.
  • The cord was compressed with multiple short segments of myelopathic signal change.

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  • A 70-year-old patient presented with a mild myelopathy affecting the lower limbs.
  • CT showed extensive calcification and thickening of the posterior longitudinal ligament, which returned low signal on all MRI sequences.
  • The cord was slightly flattened but there was no T2-hyperintense myelopathic signal change.

Treatment

  • Surgical decompression (anterior or posterior) for progressive myelopathy. CT best shows the ossified ligament, which is T2-hypointense/low signal on all MRI sequences

Differential diagnosis

Differential Diagnosis Differentiating Feature
Diffuse Idiopathic Skeletal Hyperostosis (DISH) Primarily affects anterior longitudinal ligament; OPLL affects posterior longitudinal ligament
Degenerative Disc Disease Typically affects intervertebral discs; OPLL involves ossification of ligament
Cervical Spondylotic Myelopathy Caused by degenerative changes; OPLL is a specific ossification process
Ankylosing Spondylitis Primarily affects sacroiliac joints and spine; OPLL is localised to posterior longitudinal ligament
Spinal Cord Tumour Presents as a focal mass; OPLL shows continuous or segmental ossification along the ligament
Herniated Cervical Disc Acute onset, typically at a single level; OPLL is chronic and often multi-level
Rheumatoid Arthritis of the Cervical Spine Affects facet joints and atlantoaxial articulation; OPLL affects the ligament
Fluorosis Affects multiple bones and ligaments; OPLL is specific to posterior longitudinal ligament
Hypoparathyroidism Causes generalized ligament calcification; OPLL is localised to posterior longitudinal ligament
Ossification of the Ligamentum Flavum Affects ligamentum flavum; OPLL affects posterior longitudinal ligament

  1. Le et al. Ossification of the Posterior Longitudinal Ligament: Pathophysiology, Diagnosis, and Management. 2022. The Journal of the American Academy of Orthopaedic Surgeons - Open in new tab. ↩