Posterior ring apophyseal fracture

Posterior ring apophyseal fracture or separation, also called limbus fracture, occur in the immature skeleton, most commonly in the lumbar spine. They represent bony fractures of the vertebral body rim at the site of attachment of the Sharpey fibres of the intervertebral disc.

Terminology

Not to be confused with a limbus vertebra. 

Epidemiology

Typically, adolescent males practising sport activities.

Clinical presentation​

• back pain
• sciatica
• muscle weakness related with root innervation
• association with Scheuermann disease

Pathology

The ring apophysis is a secondary ossification centre of the vertebral endplate connected to the intervertebral disc. It is firmly attached to disc fibrous annulus through Sharpey fibres and its ossification occurs at 4-6 years old.

In the first years of life, the junction between ring apophysis and the rest of vertebral body is made through a cartilage layer, that is only completely ossified around 18 years old, and this is a weak point.

The pathophysiology remains unclear. Whilst, although trauma (acute avulsion fracture vsand/or chronic repetitive traction) is considered most likely. Other hypotheses suggest degenerative component, disc herniation, avascular necrosis, traction apophysitis, etc ⁵.

Classification

They can be classified as follows:

• type I: avulsions of the posterior cortical vertebral rim
• type II: central cortical and cancellous bone fractures
• type III: lateralised chip fractures
• type IV: span the entire length and breadth of the posterior vertebral margin between the endplates

Radiographic features

CT

Considered bestCT is excellent for bony detail and is therefore usually the first line imaging modality. Findings include:

• osseous fragment displaced posteriorly to endplate with rectangular or arc-shaped morphology on axial plane
• posterior endplate defect
• posterior disc herniation

MRI

• high T2/STIR signal of acute fracture
• corner defect on posterior endplate margin
• disc degeneration and loss of height
• best method to evaluate nerve root / cauda equina compression

Differential diagnosis

On imaging consider:

• Schmorl's node
• disc calcification/ossification
• calcified disc fragment
• posterior osteophyte