Annular Epiphysis: Anatomy, Location and Imaging Appearance

Topic

Annular epiphysis

The annular epiphysis (vertebral ring apophysis) is a secondary ossification center forming a thin bony ring at the superior and inferior margins of the vertebral body endplates. It plays a key role in vertebral growth, endplate stability, and attachment of the outer fibers of the intervertebral disc.

It is an important structure in pediatric and adolescent spine anatomy and a common site involved in traction-related changes and ring apophyseal variants seen on imaging.

Synonyms

Vertebral ring apophysis
Ring epiphysis of the vertebral body

Location

Situated at the peripheral margins of the vertebral body endplates
Forms a circumferential ring along the superior and inferior endplates
Between the vertebral body and the outer annulus fibrosus
Present at each vertebral level from cervical to lumbar spine
Deep to the anterior and posterior longitudinal ligaments

Anatomical components

Thin circumferential bony rim
Superior annular epiphysis
Inferior annular epiphysis
Attachment site for:
- Outer fibers of the annulus fibrosus
- Sharpey-type collagen fibers

Relations

Superiorly:

Intervertebral disc endplate

Inferiorly:

Vertebral body cancellous bone

Anteriorly:

Anterior longitudinal ligament
Anterior annulus fibrosus

Posteriorly:

Posterior annulus fibrosus
Posterior longitudinal ligament (near midline)

Laterally:

Peripheral annulus fibrosus

Developmental anatomy

Not present at birth
Appears between 5–10 years of age as a secondary ossification center
Progressive ossification during adolescence
Fusion with vertebral body: Usually between 18–25 years
May remain partially visible in young adults as a normal variant

X-ray appearance

Spine radiographs (AP / lateral views):

Annular epiphysis: Thin, linear bony rim along vertebral endplate margins
Appearance: Smooth, well-corticated ring
Age dependence: More conspicuous in children and adolescents
Fusion: Disappears after complete fusion with vertebral body

CT appearance

Pre-contrast CT:

Annular epiphysis: Thin hyperdense bony ring at the vertebral endplate periphery
Margins: Well-defined cortical outline
Relationship: Clearly separated from central endplate in skeletally immature patients
After fusion: Appears continuous with the vertebral body cortex