A limbus vertebra is a well-corticated unfused secondary ossification center of the vertebral body, usually of its anterosuperior corner, that occurs secondary to herniation of the nucleus pulposus through the vertebral body endplate beneath the ring apophysis (see ossification of the vertebrae). These are closely related to Schmorl nodes and should not be confused with limbus fractures or infection.

Limbus vertebrae should be well-corticated, that is they have a sclerotic margin, are triangular in shape and occupy the expected location of a normal vertebral body corner, with a smooth sclerotic subjacent corticated vertebral margin. The 'fragment' of bone will not 'fit' into the adjacent bone as one would normally expect with a fracture and will often appear to be too small.

A limbus vertebra of the anterosuperior corner of a single vertebral body in the mid lumbar spine is the most common presentation. The anteroinferior and posteroinferior corners are seen far less frequently. Occasionally it may be seen in the thoracic spine.

Usually, radiography with or without CT or MRI is sufficient for diagnosis. Initially, the etiology was confirmed with discography where contrast extends into the intraosseous herniation of the nucleus pulposus.

History and etymology

The term limbus is a direct borrowing from the Latin word meaning fringe, as in the edge of something, or hem ³. Interestingly, limbus vertebra was first described by Schmorl in 1927 ⁴.

Differential diagnosis

Consider

intercalary bone: ossification is in the anterior annular fibers of an intervertebral disc
acute fractures: should have an adjacent perivertebral hematoma
- limbus fracture
- teardrop fracture (cervical spine)
degenerative disease of the spine
infection: adjacent cortical loss and soft tissue mass