OPLL

Numbers

Incidence of OPLL in

Asian populations at 2.4%,

Japan reporting the highest rates.

non-Asian populations 0.16%

OPLL is twice as common in men as in women, and

Symptomatic OPLL typically presents in the 5th to 6th decade of life.

Associated Diseases

Musculoskeletal conditions

DISH or Forestier disease

One study found OPLL in 50% of patients with DISH.

Rare cases include DISH with continuous-type OPLL leading to cervical myelopathy and hypermobility at C1–2 after multilevel fusion.

Ankylosing spondylitis
Other spondyloarthropathies.

Schizophrenia

20% have OPLL

Observed in dizygotic twins.

Down syndrome

Pathology

OPLL form through endochondral ossification.

Histopathologically, it is primarily composed of lamellar bone with mature Haversian canals.

Ultrastructural studies of the ligamentum flavum in OPLL patients reveal

atrophic elastic bundles,
microfibril disappearance,
irregular collagen fibril alignment,
Extracellular plasma membrane-invested particles resembling matrix vesicles.

Hypertrophy of the posterior longitudinal ligament is considered an early stage of OPLL,

showing similar histological and biochemical characteristics, including staining by BMP and TGF-β.

OPLL patients often exhibit increased overall bone mineral density (BMD), although BMD may decrease with advancing OPLL.

Pathogenesis

Poorly understood but some theories are present

Cellular Characteristics:

Ligament cells from OPLL patients exhibit osteoblast-like characteristics, including high alkaline phosphatase activity and responsiveness to calcitonin and calcitriol.

Genetic Factors:

Given the higher prevalence in Asian populations, genetic factors are suspected.
Specific collagen genes, such as (not all study results are reproduce-able)

Human collagen α2 gene (COL11A2) on chromosome 6p
Collagen 6A1 gene (COL6A1) on chromosome 21q22.3

NPPS gene (nucleotide pyrophosphatase) mutations

which produces an inhibitor of calcification, have also been linked to OPLL development in mouse models, though later human studies have shown conflicting results.

Other genes, including human retinoic X receptor β, TGFβ, BMP4, vitamin D receptor gene, promyelotic leukemia zinc finger gene, and RUNX2, have anecdotal links to OPLL.

Hormonal Factors:

Bone morphogenetic proteins (BMPs), known for inducing ectopic bone and cartilage formation, are believed to be significant.

BMP receptors are increased in ossified ligament tissue,
BMP-2 stimulates osteogenic differentiation in ligament cells from OPLL patients.

Polymorphisms in the BMP-2 gene have shown associations with genetic susceptibility and severity of cervical OPLL in certain populations.

Transforming growth factor-β (TGF-β1) polymorphisms, OPLL predisposition or the extent of ossification.
Elevated serum levels of menatetrenone and activin have been correlated with OPLL formation.

Biomarkers:

Upregulated serum biomarkers (e.g., PRO2675, human serum albumin complexes, proapolipoprotein, retinol binding protein)
Downregulated one (α1-microglobulin/bikunin precursor)
Increased serum procollagen Type I carboxyl-terminal peptide and intact osteocalcin have also been demonstrated.

Metabolic Factors:

Non–insulin-dependent diabetes mellitus is suggested as a risk factor,

Insulin potentially inducing osteogenic differentiation in spinal ligament cells.

Environmental Factors:

Mechanical stress in spinal ligaments has been investigated as a factor in OPLL development and progression.

Mechanical stress can induce osteogenic differentiation and gene expression of various proteins, including alkaline phosphatase, osteopontin, BMPs, and Type I collagen.

Lifestyle Factors:

Increased risk of OPLL.

Frequent consumption of pickles,
non-daily rice consumption,
family history of myocardial infarction,
high body mass index at age 40,
long working hours, and night shifts

Decrease risk of OPLL

Frequent consumption of chicken and soy products,
Good sleeping habits

Natural History

Symptomatic OPLL is typically detected in elderly patients.

OPLL progression rates,

56.5% at 2 years for cervical OPLL,

being more common in younger patients with continuous- and mixed-type OPLL.

The rate of progression can vary, with some studies showing rapid progression in the 4th decade of life that gradually decreases later.

Long-term follow-up (mean 17.6 years):

Only 17% of patients initially without myelopathy developed it during the follow-up, suggesting that prophylactic surgery for asymptomatic patients is unnecessary.

Factors associated with myelopathy development;

Static factors

All patients with more than 60% spinal canal stenosis on plain radiography developed myelopathy,

Dynamic factors

Those with myelopathy had significantly greater range of motion.
Trauma can also induce sudden-onset myelopathy in patients with mixed or segmental type OPLL.

Clinical Presentation

The clinical presentation of OPLL depends on the

size of the ossification,
spinal canal diameter,
Spinal range of motion.

Patients can be asymptomatic, or present with neurological deficits such as radiculopathy, myelopathy, and in severe cases, bowel and bladder symptoms.

Symptom onset is usually gradual, but trauma can lead to sudden-onset myelopathy.

Tandem Ossification:

Thoracic tandem ossification (including thoracic OLF and/or OPLL) was found in 33.8% of patients with cervical OPLL, suggesting the need for simultaneous thoracic spine studies.

Classification

Four types based on lateral plain radiography:

A. Continuous type: A long lesion extending over several vertebral bodies.
B. Segmental type: One or several separate lesions behind the vertebral bodies.
C. Mixed type: A combination of continuous and segmental types.
D. Circumscribed type: The lesion mainly located posterior to a disc space.

Radiological Evaluation

Plain Radiography:

Simplest for detection but has limitations in reliability for classification, particularly for continuous-type OPLL.

Useful for detecting and accurately locating OPLL, precisely depicting dimensions and extent of spinal canal stenosis.
A "mushroom or hill shape" on axial CT and a sharp radiolucent line between the vertebral body and ossified ligament are characteristic.
Dural ossification

CT is superior to MRI for detecting dural ossification

Associated with a higher incidence of new neurological deficits and CSF leakage during anterior decompression.

Non-segmental cervical OPLL is most likely associated with dural ossification.

Double-layer sign on bone window CT (anterior and posterior rims of hyperdense ossification separated by a central hypodense mass) is more pathognomonic for dural penetration than a single-layer sign.

In thoracic OPLL, dural ossification is even more common (80% rate) and can be detected in both segmental and non-segmental types.
Min 2007:

Dural defects were present in

52.6% double-layer signs
13.6% with single-layer signs

A: The double-layer sign, consisting of anterior and posterior ossified rims separated by a centrally hypertrophied PLL. In the axial view, the double arrow shows the method of measurement of the central hypodense mass, and in the sagittal view the arrow points to the level being demonstrated in the axial view. B: The single-layer sign, consisting of a single homogeneous ossified PLL mass. In the sagittal view, the arrow points to the level being demonstrated in the axial view.

Upper: Double-layer sign, consisting of anterior and posterior ossified rims separated by a centrally hypertrophied PLL.
Lower: Single-layer sign, consisting of a single homogeneous ossified PLL mass.

Not used for diagnosing small ossified lesions due to signal hypointensity on T1- and T2-weighted images.
MRI is sensitive for:

Associated disc protrusion (found in 60% of cervical OPLL cases, 81% in segmental type)
Determining the actual level of spinal cord compression → guiding surgical treatment.

Signal hyperintensity on T2 correlates with

More severe neurological deficits
Poor neurological outcomes if it expands postoperatively.

Matsuyama spinal cord shape classification

Matsuyama 2004.pdf

112.5 KB

Predicing neurological recovery after laminoplasty for OPLL

Triangular shape having the worst prognosis and least expansion after surgery.

Intermediate for those with boomerang

Best for those with teardrop shape

Management

Conservative

Typically symptomatic, involving pain medication, anti-inflammatory drugs, and opioids.

Surgical Management of Cervical OPLL

Surgical Procedure	Advantages	Disadvantages
laminectomy	simple, less operative time & blood loss, low immediate complication	risk of OPLL progression; risk of kyphotic deformity, spinal instability, & neurological deterioration due to scar tissue formation; ineffective in severe kyphosis & large OPLL
laminectomy w/ fusion	relatively simple, low complication rate, decreased risk of kyphotic deformity & spinal instability	risk of OPLL progression, ineffective in cases w/ severe kyphotic deformity & large OPLL
laminoplasty	relatively simple, low complication rate compared w/ ant approach, decreased risk of kyphotic deformity, spinal instability & neurological deterioration due to scar tissue formation compared w/ laminectomy alone	risk of OPLL progression, limited effectiveness in cases w/ severe kyphotic deformity & large OPLL
ant approach	direct ant decompression of OPLL	high complication rate (neurological deterioration, graft complication, CSF leakage), limitation in cases w/ long segment OPLL or OPLL involving C-2
combined ant & pst approach	direct ant decompression of OPLL	more op time & blood loss

Decision of approach

Surgical decision making

Fujiyoshi 2008

For patients in the K-line (-) group, posterior approach surgeries are not appropriate, and anterior decompression surgery is recommended as the first choice.

Shin 2025

Anterior decompression with fusion (ADF) consistently yielded the best outcomes in K line + or K line - group

For patients with COR ≥ 50% and/or K-line (+), laminoplasty (LP) was found to be optimal.
For patients with COR ≥ 50% and K-line (-), laminectomy with fusion (LF) offered better results than laminoplasty.

Gabriel Lu- Cervical Spine Research Society 2025 presentation

Indication:

Anterior Surgery

1-2 or 3 levels are affected.
≥60% compression is present.
The C2-C7 Sagittal Vertical Axis (SVA) is > 4 cm.
The spine is kyphotic.
There's significant radicular pain or neck pain.

Posterior Non-Fusion (Laminoplasty)

For ≥4 levels of disease
<60% COR
The spine is lordotic (k-line positive).
There is minimal pain.
The C2-C7 SVA is < 4 cm.
The C7 SVA is < 5 cm.
The T1-S CL is < 20.

Posterior Decompression and Fusion

> 3(4) levels are affected.
The spine is kyphotic (k-line negative), painful, and has mixed opacity.
>60% COR.
There is deformity or an adjunct to multilevel posterior anterior corpectomies reconstruction.
The C2-C7 SVA is > 4 cm.
The C7 SVA is > 5 cm.
The T1-S CL is > 20.

Combined Anterior and Posterior Approach

There is multilevel rigid cervical kyphotic deformity.
The anterior cord has >60% compression.

K (kyphosis) - line

Fujiyoshi 2008.pdf

368 KB

Definition:

The K-line is defined as a straight line that connects the midpoints of the spinal canal at C2 and C7.

How to draw:

This line is typically drawn on lateral cervical radiographs in the neutral position or on midsagittal T2-weighted magnetic resonance images if C7 is obscured.

Cord movements

For many K-line (+) patients, a sufficient posterior shift and decompression can be expected even with posterior surgeries
Sufficient posterior shift of the spinal cord and neurologic improvement will not be obtained after posterior decompression surgery in the K-line (-) group.

K-line Classification

K-line (+) group:

OPLL does not exceed the K-line and remains within the ventral area
meaning there is space between the K-line and the OPLL.

K-line (-) group:

OPLL exceeds the K-line and has grown beyond it.
This can occur with a large OPLL size or even an intermediate OPLL size if the cervical spine alignment is kyphotic

COR (canal occupancy rate)

Calculation: COR was determined by calculating the maximum thickness of the OPLL as a percentage of the anteriorposterior diameter of the spinal canal at the site of the primary OPLL lesion

Outcome

Shin 2025

Shin 2025.pdf

1.7 MB

Overall better JOA recovery was observed in patients who were K-line (+) and in those with a low Canal-Occupying Ratio (COR < 50%).

In patients with a high COR (≥ 50%), K-line (-) status was associated with poorer neurological recovery.
When the COR was low (< 50%), outcomes were similar regardless of K-line status.

In cases of high COR, K-line status was influenced by cervical alignment, C2 slope (C2S), and T1 slope (T1S).
In cases of low COR, K-line status was mainly affected by the COR percentage itself.

Patients who were K-line (+) showed significantly greater C2–7 Cobb angle (CA) both preoperatively and postoperatively compared to K-line (-) patients.
The COR was significantly lower in the K-line (+) group than in the K-line (-) group (p< 0.001).
JOA recovery rate was significantly higher in the K-line (+) group (p< 0.001).
Following posterior decompression, improvement in JOA score was greater in K-line (+) patients than in K-line (-) patients.
No significant difference in JOA recovery was observed between K-line groups following ADF.
In the K-line (-) group, ADF resulted in significantly better neurological outcomes than posterior decompression (p< 0.001).
Among patients with COR < 50%, the JOA recovery rate did not significantly differ between K-line (+) and K-line (-) groups (p= 0.952).
Among patients with a COR ≥ 50%, K-line (+) patients had significantly higher recovery rates than K-line (-) patients (p= 0.038).
In the COR ≥ 50% group, the K-line (-) group had significantly lower C2–7 CA and higher C2S and T1S, suggesting that K-line status in high COR cases is influenced by cervical sagittal alignment.
ADF was associated with an increase in postoperative C2–7 CA, while LP led to a decrease, and LF maintained alignment.
Range of motion (ROM) was most restricted after LF and ADF and best preserved with LP.
ADF had a longer operative time than LP but shorter than LF, while intraoperative blood loss was lowest in LP and highest in LF.
ADF was associated with a higher rate of pseudoarthrosis and revision surgery, while LF had the highest incidence of C5 nerve palsy.

Wang 2024 (meta-analysis)

Improved Prognosis and Clinical Outcomes for K-line (+) Patients in patients with multi-segmental cervical OPLL compared to a negative K-line.
K-line (+) had better mJOA Score Recovery Rate than a K-line (-).
K-line (+) patients had a significantly lower NDI (Neck Disability Index)

Posterior Approach

Laminectomy:

Advantages:

Simple
Less operative time and blood loss
Low immediate complication risk.

Disadvantages:

Risk of postoperative kyphotic deformity (though it may not affect neurological outcomes),
Spinal instability
Neurological deterioration due to scar tissue formation
Limited effectiveness in severe kyphosis or large OPLL.

OPLL progression after laminectomy rarely causes neurological deterioration.

A rare case of incarcerated spinal cord herniation post-laminectomy has been reported.

Laminectomy with Fusion:

Advantages:

Decreases the risk of postoperative kyphotic deformity and spinal instability compared to laminectomy alone.
Functional improvement is similar to laminectomy or laminoplasty.
Fusion rates can be high (100% with spinous process wiring) with low complications.

Disadvantages:

Higher operative duration and intraoperative blood loss with pedicular screw fixation compared to laminoplasty.
Risk of neurovascular injury, particularly with pedicular screws.
C5 nerve root palsy can occur and is correlated with increased cervical lordosis, with tethering being a main pathogenic mechanism.

Laminoplasty (Open-Door and Double-Door):

Advantages:

Reduced risk of postoperative kyphotic deformity and neurological deficit from scar tissue formation compared to laminectomy.
Relatively simple, low complication rate compared to anterior approaches.

Disadvantages:

Restricted access to the hinged side (open-door),
Potential for laminar door closure (reclosure rate of 34% with traditional methods)

use plates or bone to keep door open

Axial neck pain
Loss of cervical spine range of motion

can be reduced with early mobilisation of the neck

Risk of OPLL progression
Limited effectiveness in severe kyphotic deformity and large OPLL.

Modifications:

Techniques to prevent closure include spacer insertion (bone graft or hydroxyapatite) and rigid fixation with titanium miniplates.

Adequacy of Decompression:

Intraoperative ultrasonography can evaluate decompression adequacy;
OPLL thickness > 7.2 mm may indicate insufficient decompression, though this didn't correlate with 2-year neurological outcomes.

Expansion & Indications:

Open-door laminoplasty can produce a significantly larger expansion ratio at C-6 than double-door.

Indications for open-door include

CSM with hemilateral radiculopathy
Large OPLL prominence
Tiny spinous processes.

Double-door

Indications

Usual CSM
Small/slight OPLL prominence
CSM with bilateral radiculopathy
Cervical canal stenosis with instability requiring instrumentation.

Long-term Outcomes:

Recovery rates varied from 47.9% to 63.1% in studies with >5 years follow-up. Neurological function significantly improves post-surgery, is maintained for 5 years, and then may slightly decline.

Factors influencing outcomes:

Duration and severity of myelopathy, age, preoperative kyphosis, occupying ratio > 60%, and hill-shaped ossification.
Postoperative changes in cervical alignment and OPLL progression show controversial results.

Range of Motion (ROM):

Postoperative cervical ROM decreases by approximately 32% after laminoplasty.

This loss is time-dependent, plateauing by 18 months, and does not correlate with postoperative axial neck pain.

Anterior Approach

General

Advantages:

Direct anterior decompression of OPLL.

Disadvantages:

High complication rate

Neurological deterioration
Graft complications
CSF leakage

Limited use in long segment OPLL or OPLL involving C-2.

Anterior Cervical Discectomy with Fusion (ACDF):

Procedure of choice for OPLL with associated disc herniation (present in 60% of cases).

Recovery rates range from 51% to 63.2%.

Endoscopic ACDF has cosmetic and visualisation advantages but is limited to C4–6 levels due to anatomical constraints and risk of thyroid vessel damage.

Multilevel OPLL is a contraindication.

Corpectomy (various techniques):

Anterior cervical corpectomy with fusion:

Neurological improvement rates vary from 51% to 71.7%.
Poor-grade patients (Nurick Grade 4 and 5) can achieve neurological improvement (76%).
Different graft materials (iliac crest, vertebral body, interbody fusion cages) have been used, with vertebral body grafts being the most fragile.

Anterior interbody fusion without decompression:

Effective for segmental or nodular type OPLL, suggesting dynamic factors contribute to myelopathy.

Open-window corpectomy: Ozer 1999

perform discectomy and then make large fishmouth vertebral body decompression to decompress the deep vertebral body facing the theca to achieve decompression.

Creates a stable construct with 3-point fixation and offers better load sharing.

Satisfactory clinical and radiological outcomes reported.

Vertebral body sliding osteotomy (VBSO)

Oblique corpectomy: Preserves the ventral half of the vertebral body, potentially avoiding fusion. Provides wide exposure for OPLL resection while preserving spinal stability. Intraoperative ultrasonography is helpful for identifying vertebral artery and approach trajectory but has limitations due to artefacts from residual ossification. Can be used for combined OALL and OPLL.

Skip corpectomy: (e.g., C-4 and C-6 corpectomy with C-5 preservation) used for multilevel CSM and cervical OPLL. Improved JOA scores and strengthened construct by preserving C-5 vertebral body for screw purchase.

Wide transvertebral approach with ceramic insertion: Preserves intervertebral disc movement. Successful for segmental-type OPLL but has a narrow visual field and is not for instability or continuous/combined OPLL.

Prevascular extraoral retropharyngeal approach:

Reported as relatively safe for the upper cervical spine (C2–4 OPLL), with low rates of permanent dysphagia.

Combined Anterior and Posterior Approach:

Advantages:

Direct anterior decompression of OPLL.

Disadvantages:

More operative time
More blood loss.

Surgical Management of Thoracic OPLL

Surgical outcomes for thoracic OPLL are generally poorer than for cervical OPLL due to several factors:

Natural kyphosis restricts backward shift of the spinal cord after posterior decompression.
Thoracic spinal cord is relatively avascular, making it more vulnerable to ischemic injury.
Ribcage restricts surgical approaches.

Surgical Options:

Posterior decompressive Laminectomy:

Disadvantages:

Indirect decompression, high risk for postoperative paraparesis and late neurological deterioration.
Disrupts posterior tension band, leading to instability.

Simultaneous posterior instrumented fusion is recommended due to dynamic factors and kyphosis progression.
Beak-type OPLL has a higher risk of neurological deterioration than flat-type OPLL after posterior surgery.

Laminoplasty:

Can be used safely for thoracic OPLL at the nonkyphotic upper thoracic spine (T1–4).
Mean recovery rate of 54.5% reported, with cases of transient motor paralysis.

Posterior Decompression with Fusion:

Advantages:

Generally lower complication rates and neurological deterioration compared to posterior decompression alone or OPLL extirpation.
No cases of postoperative paralysis or late neurological deterioration were observed in one study.

Outcomes:

Mean recovery rate of 58.1%, with maximal recovery typically around 9 months.
Considerable neurological improvement is expected despite persistent spinal cord impingement.

Kyphosis Correction:

Posterior decompression with 5°–15° kyphosis correction with instrumented fusion has shown complete decompression and backward shift of the spinal cord without aggravated myelopathy.
Recovery rates vary from 56% to 68%.
An ossification-kyphosis angle > 23° at the decompression site indicates insufficient USS echo-free space.

all patients with < 23° had echo-free space

Anterior Approach (Thoracic):

Advantages:

Direct OPLL removal.

Disadvantages:

Technically demanding,
poor surgical results,

especially in severe preoperative spinal cord compression.

High complication rates

Neurological deterioration (10.5%)
CSF leakage (31.6%).

Poor outcomes associated with poor preoperative JOA scores and immediate postoperative neurological deterioration.

Circumspinal Decompression through Posterior Approach:

Advantages:

Immediate anterior and posterior decompression and/or stabilisation in a single operation.

Disadvantages:

Technically demanding,

More operative time
More blood loss.

High complication rates:

40% dural tear,
10% deep infection
33% postoperative neurological deterioration.

Decompression of 5 or more vertebral levels associated with poorer outcomes.

Staged Posterior Approach Surgery:

Addresses anatomical factors inhibiting posterior shift of the spinal cord (longitudinal factors like anterior pulling effects and dorsal dura restraining effects; axial factors like anterior dural adhesion to OPLL, dural ossification, and anterior tethering effect of thoracic roots/dentate ligaments).
First stage:

Extensive cervicothoracic laminoplastic decompression, with or without posterior longitudinal durotomy, to eliminate longitudinal factors.

Second stage (if inadequate decompression):

Elimination of axial factors through root release with total laminofacetectomy and anterolateral dural release, with or without OPLL resection.

Advantages:

Safety, allowing preparation of severely compressed spinal cord before extensive manipulation.
Neurological improvements comparable to successful anterior approaches.

Factors correlate with better surgical outcomes (Thoracic OPLL):

Shorter duration of symptoms
Milder myelopathy

Surgical Management of Lumbar OPLL

Most cases use a posterior approach.

Symptomatic lumbar OPLL usually occurs in the upper lumbar spine due to the broader posterior longitudinal ligament

Presents with cauda equina syndrome.

Combined anterior-posterior surgery is recommended for large OPLL occupying much of the spinal canal.