Apophysis

an outgrowth of a bone, such as a tubercle, process or tuberosity, which usually has never been separated from the parent bone. Apophyses are found on numerous bones. Also, see apophysis.

2. Pathology

In the spine, both the superior and the inferior vertebral endplates have narrow cartilaginous swellings termed ring apophysis, which play a role in traction. Avulsions and fractures of the apophyseal ring occur as a result of trauma and may cause low back and leg pain. Fractures occur most commonly in the inferior ring apophyses of the lower lumbar vertebrae. These lesions are very hard to see on conventional radiographs, but on CT scans the fracture has a characteristic appearance, having an arcuate or semilunar configuration paralleling the posterior border of the vertebral body.

In children, the apophyseal growth centres tend to consist of fatty (yellow) marrow throughout life. MR imaging is useful in differentiating red (haematopoietic) from yellow (fatty) marrow on the basis of signal intensity differences.

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