OPLL (Ossification of Posterior Longitudinal Ligament)

Definition OPLL is a hyperostotic condition characterized by calcification and ossification of the posterior longitudinal ligament. It results in spinal canal stenosis and myelopathy.

Etiology

• Genetic: Strong familial inheritance. Associated with collagen genes (COL11A2, COL6A1).
• Metabolic: Associated with Diabetes (NIDDM), Obesity, and DISH.
• Mechanical: Stress on the ligament may trigger osteogenesis.

Pathology

• Begins as hypertrophy of the ligament.
• Progresses to cartilaginous proliferation.
• Ends in enchondral ossification.
• Can penetrate the dura mater ("Dural Ossification"), making surgical separation impossible without dural resection.

The Posterior Longitudinal Ligament (PLL)

• Runs along the posterior aspect of the vertebral bodies (within the canal).
• Acts to prevent hyperflexion.
• In OPLL, it becomes a space-occupying lesion anterior to the cord.

The K-Line (Kyphosis Line)

• A virtual line drawn on a lateral Neutral X-ray.
• Start: Midpoint of C2 Spinal Canal.
• End: Midpoint of C7 Spinal Canal.
• Significance: Defines the anterior limit of the spinal canal.
• K-Line Positive: The OPLL mass lies ANTERIOR to the line. (Good for posterior surgery).
• K-Line Negative: The OPLL mass CROSSES the line. (Posterior surgery will fail as cord cannot drift back past the mass).

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Presentation

• Similar to CSM but often more severe/rapid once symptomatic.
• Myelopathy: Hands (clumsy), Gait (ataxic), Bladder (late).
• Radiculopathy: Can occur if lateral extension involves roots.
• Trauma: Acute quadriplegia after minor fall is a classic presentation (stiff spine + stenosis).

Examination

• UMN signs (Hyperreflexia, Clonus, Hoffman's).
• Limited ROM (Stiff neck - often has DISH).

The workup above repeatedly relies on "canal occupancy" and the ossification "shape (beak/hill/mushroom)" as prognostic levers, but neither is defined. Both are measured on the CT and both predict whether a cord will become myelopathic and how it will respond to surgery, so they deserve to be spelled out.

The occupying ratio (OR). This is the single most-quoted number in OPLL. It is the maximum antero-posterior thickness of the ossified mass divided by the antero-posterior diameter of the spinal canal at the same level, expressed as a percentage (measured on the mid-sagittal CT or axial bone window):

Occupying ratio = (AP thickness of OPLL ÷ AP canal diameter) × 100

A higher ratio means less reserve space for the cord. A ratio approaching or exceeding about 60% is the classic threshold associated with a high likelihood of myelopathy and a poorer natural history; combined with dynamic factors (segmental mobility on flexion-extension) it is one of the radiographic predictors of deterioration that push towards surgery rather than observation. A very high ratio also argues against posterior surgery alone, because even a fully drifted cord can remain draped over a large anterior mass.

The shape of the mass. Two masses with the same occupying ratio do not behave the same way - the cross-sectional shape matters:

Lateral deviation of the mass off the midline is an additional warning sign: an asymmetric beak loads one side of the cord and limits the uniform posterior drift that laminoplasty depends on, so a laterally-deviated, high-ratio beak is one of the patterns that tips the decision toward an anterior or circumferential strategy.

Observation

• Many patients have OPLL incidentally.
• Progression rate is slow but steady.
• Contraindications to observation: Progressive myelopathy (mJOA score dropping), acute onset.
• Advice: Avoid contact sports, fall prevention, collar for comfort only.

The evidence base and the controversies section both invoke ACAF, yet the technique is never described. It is the most important recent addition to OPLL surgery and a high-yield viva topic, because it is designed specifically to solve the problem that makes anterior corpectomy so dangerous: peeling a dura-adherent ossified mass off the cord.

The core idea. In a conventional corpectomy the surgeon removes the vertebral bodies and then tries to resect the OPLL, risking a massive unrepairable dural tear. ACAF instead moves the whole vertebral-body-plus-OPLL complex forward as a single unit rather than removing the ossified mass at all:

1. Anterior plate and screws are positioned first, with the screws set to the intended new (anterior) position.
2. The vertebral bodies bearing the OPLL are isolated by bilateral longitudinal osteotomies/grooves at the body-pedicle junction, and the discs above and below are released, freeing a "bone-OPLL complex".
3. The freed complex is then lifted (ante-displaced) anteriorly and held in its new forward position by tightening it down onto the pre-contoured plate.

Because the OPLL is never separated from the dura - the cord is decompressed by translating the whole anterior wall forward - the dreaded step of stripping ossified dura is avoided, which is the rationale for ACAF's lower CSF-leak profile in difficult, dura-adherent disease.

What the evidence shows. A meta-analysis of multilevel cervical OPLL (Zhang, PMID 38157983: 7 studies, 467 patients) found that, compared with laminoplasty, ACAF gave higher JOA scores and improvement rate, better restored cervical lordosis, and lower rates of C5 palsy and axial symptoms, with less blood loss - at the cost of longer operative time and more dysphagia, and with no significant difference in CSF-leak or overall complication rate. ACAF is therefore an attractive option for multilevel, high-occupancy, K-Line-negative or dura-adherent OPLL where both a corpectomy and a laminoplasty are problematic, accepting a swallowing-morbidity and learning-curve trade-off.

• CSF Leak Protocol: If leak suspected/confirmed: Flat bed rest 24-48hrs. Acetazolamide. Lumbar Drain if persistent.
• Collar: Aspen collar 6 weeks (especially if fusion).
• Neuro Rehab: Intensive gait training.

• Surgical Outcome: Generally good if K-Line respected.
• Recurrence: OPLL mass continues to grow in 20% of cases, especially with Laminoplasty (motion preserved). Fusion arrests growth.
• Poor Prognostic Factors:
  • Diagnosis over 60 years.
  • Myelopathy duration over 1 year.
  • Massive canal occupancy (greater than 60%).
  • Trauma-induced onset.
  • High intramedullary signal intensity on T2 MRI.
  • Diabetes Mellitus (Poor wound healing, infection risk).

Progression Rates:

• Longitudinal studies show OPLL grows 2mm/year in 10% of patients.
• Anterior fusion stops this growth in the fused segments, but adjacent segment disease is accelerated.
• Laminoplasty allows continued growth, but usually the canal expansion is sufficient to accommodate it.

Global epidemiology

• Prevalence is strongly ethnicity-dependent: 1.9-4.3% in Japanese adults over 30 (Matsunaga, Spine 2012), and broadly 0.4-3% across East Asian populations (Japan, Korea, China, Taiwan).
• Much lower in populations of European and African descent (roughly 0.1-1.7%), but rising with CT use and ageing — OPLL should be on the myelopathy differential worldwide, not only in East Asian patients.
• Male predominance (about 2:1), peak presentation in the 5th-7th decades, strong associations with type 2 diabetes, obesity, and DISH.

Side-by-side guideline / consensus positions

Registry / outcome evidence

• Unlike arthroplasty, there is no dedicated implant registry for OPLL; the evidence base is dominated by large Japanese multicentre cohorts and meta-analyses (e.g. ACAF vs laminoplasty, Zhang 2024).
• Cohort data consistently show anterior reconstruction yields higher neurological recovery but greater approach-related morbidity, while posterior decompression is safer and faster.

High- vs limited-resource practice variation

• High-resource settings: routine pre-operative CT and MRI, intra-operative neuromonitoring, ultrasonic bone scalpels and microscopes for floating-method anterior surgery.
• Limited-resource settings: reliance on plain films and MRI (CT may be limited); laminectomy or laminoplasty is often preferred as a lower-risk, lower-cost option even when anterior surgery might give marginally better recovery, because dural-tear and CSF-leak management is resource-intensive.
• Trauma context: in any setting, a rigid OPLL/DISH spine is at high risk of central cord syndrome after minor hyperextension — fall prevention and early imaging of new deficits are universal priorities.

• Asymptomatic / prophylactic surgery: How aggressively to treat high canal-occupancy OPLL before myelopathy develops remains debated. High occupancy and dynamic instability predict deterioration, but prophylactic surgery carries real risk and is not universally endorsed.
• Anterior versus posterior for multilevel disease: Anterior reconstruction (corpectomy, ACAF) tends to give better neurological recovery but more approach-related morbidity (dysphagia, CSF leak, graft issues); posterior surgery is safer and faster. There is no single correct answer — alignment (K-Line), occupancy and surgeon experience drive the choice.
• Laminoplasty versus laminectomy-and-fusion: Both decompress posteriorly. Fusion arrests OPLL progression and corrects alignment but sacrifices motion and raises C5 palsy risk; laminoplasty preserves motion but allows continued ossification growth.
• Resect versus float ossified dura: The floating (or anterior controllable antedisplacement, ACAF) philosophy of not resecting dura-adherent OPLL is increasingly favoured to avoid unrepairable dural defects, but adequacy of decompression versus leak risk is still weighed case by case.
• Steroids for C5 palsy / prophylaxis: There is no high-level evidence supporting routine steroids to prevent or treat post-decompression C5 palsy; management remains largely supportive.
• Medical modulation of progression: Identification of Wnt-pathway genes such as RSPO2 raises the prospect of pharmacological control of ossification, but no disease-modifying drug therapy currently exists.