Ossification of the Posterior Longitudinal Ligament (OPLL)¶
Definition¶
Ossification of the posterior longitudinal ligament (OPLL) is a condition in which the posterior longitudinal ligament undergoes ectopic bone formation within the vertebral canal, resulting in narrowing of the spinal canal and potential compression of the spinal cord or nerve roots. It is most common in the cervical spine and in East Asian populations.
Epidemiology¶
- Prevalence: 2–4% in Japan; 0.1–1.7% in Western populations
- Male predominance (2:1)
- Mean age of presentation: 50–60 years
- Most common location: cervical spine (C2–C5), followed by thoracic spine
- Associated with DISH (~25% of OPLL patients also have DISH), diabetes, and metabolic syndrome
Classification (Morphologic Types on CT)¶
| Type | Description | Canal Narrowing |
|---|---|---|
| Continuous | Ossification spans multiple vertebral bodies as a long, continuous bar | Most severe |
| Segmental | Ossification behind individual vertebral bodies with gaps at disc levels | Moderate |
| Mixed | Combination of continuous and segmental | Variable |
| Circumscribed | Focal ossification behind one or two vertebral segments | Least severe |
Imaging Findings¶
CT — Gold Standard for Characterization¶
- Hyperdense ossification posterior to the vertebral bodies within the spinal canal
- Best evaluated on sagittal and axial reformats
- Measure: AP thickness of OPLL, percent canal occupation, and remaining canal diameter
- Occupying ratio (OPLL thickness / AP canal diameter × 100): >60% strongly associated with myelopathy
- CT is superior to MRI for delineating the extent and morphology of ossification
MRI¶
| Finding | Appearance |
|---|---|
| OPLL mass | Low signal on all sequences (ossified bone); may have variable signal if immature ossification |
| Cord compression | Cord deformation, flattening against the OPLL mass |
| Myelopathy | T2 hyperintensity within the cord at the level of maximal compression |
| Myelomalacia | T1 hypointensity within the cord — indicates irreversible damage |
Radiography¶
- Opaque strip posterior to the vertebral bodies on the lateral view
- Subtle and easily missed — CT is far more sensitive
Clinical Pearl
OPLL presents a unique surgical challenge: anterior approaches (ACDF, corpectomy) risk dural tears because the ossified ligament is often adherent to or even fused with the dura. Posterior approaches (laminoplasty, laminectomy) avoid the ossified mass but may be less effective for severe anterior compression. The surgical approach depends on the number of levels involved, the morphologic type, and the degree of kyphosis. CT is essential for preoperative planning — it defines the OPLL morphology and identifies dural ossification (which predicts high risk of CSF leak with anterior surgery).
Key Points¶
- OPLL is ectopic ossification of the PLL within the spinal canal — most common in the cervical spine
- Higher prevalence in East Asian populations; associated with DISH and diabetes
- CT is the gold standard for morphologic classification and surgical planning
- Occupying ratio >60% strongly predicts myelopathy
- MRI is essential for evaluating cord compression and signal change
- Surgery is complex — approach depends on OPLL morphology and extent
References¶
- Abiola R, Rubery P, Mesfin A. Ossification of the Posterior Longitudinal Ligament: Etiology, Diagnosis, and Outcomes of Nonoperative and Operative Management. Global Spine Journal. 2016;6(2):195-204. https://pmc.ncbi.nlm.nih.gov/articles/PMC4771496/
- Tetreault L, Nakashima H, Kato S, et al. A Systematic Review of Classification Systems for Cervical Ossification of the Posterior Longitudinal Ligament. Global Spine Journal. 2019;9(1):85-103. https://journals.sagepub.com/doi/10.1177/2192568217720421
- Ashman C. Ossification of the Posterior Longitudinal Ligament: Bone in a Bad Place. Radsource MRI Web Clinic. August 2019. https://radsource.us/ossification-posterior-longitudinal-ligament-bone-bad-place/
- Singh H, Khanna V, Sivasankar R, Mothukuri R. Ossification of Posterior Longitudinal Ligament. Medical Journal Armed Forces India. 2004;60(3):284-286. https://pmc.ncbi.nlm.nih.gov/articles/PMC4923222/
- Gaillard F, Bell D, et al. Ossification of the posterior longitudinal ligament. Radiopaedia.org. https://radiopaedia.org/articles/ossification-of-the-posterior-longitudinal-ligament