Posterior ring apophyseal fracture
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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 fibers of the intervertebral disc.
Not to be confused with a limbus vertebra.
Typically, adolescent males practising sport activities.
- back pain
- muscle weakness related with root innervation
- association with Scheuermann disease
The ring apophysis is a secondary ossification center of the vertebral endplate connected to the intervertebral disc. It is firmly attached to disc fibrous annulus through Sharpey fibers 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, although trauma (acute avulsion and/or chronic repetitive traction) is considered most likely. Other hypotheses suggest degenerative component, disc herniation, avascular necrosis, traction apophysitis, etc 5.
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: lateralized chip fractures
- type IV: span the entire length and breadth of the posterior vertebral margin between the endplates
CT 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 is indicated where evaluation of associated soft tissue structures is required. It is the modality of choice for evaluating neural structures. Findings may include:
- high T2/STIR signal of acute fracture
- corner defect on posterior endplate margin
- disc degeneration and loss of height
On imaging consider:
- Schmorl node
- disc calcification/ossification
- calcified disc fragment
- posterior osteophyte