Morphologic aspects of the cervical (C3-C7) annular epiphysis: a skeletal study

Abstract

Background context: The annular epiphysis (AE) is a peripheral ring of cortical bone that forms a secondary ossification center in the superior and inferior surfaces of vertebral bodies (VBs). The AE is the last ossification site in the skeleton, typically forming at about the 25th year of life. The AE functions jointly with vertebral endplates to anchor the intervertebral discs to the VBs.

Purpose: To establish accurate data on the sizes of the AE of the cervical spine (C3-C7); to compare the ratios between areas and the ratios of the AE to VBs; to compare the ratios between the superior and inferior VB surface areas; and to compare AE lengths between the posterior and anterior midsagittal areas.

Study design: Measurement of 424 cervical spines (C3-C7) obtained from the skeletal collection of the Natural History Museum, Cleveland, Ohio (USA).

Methods: The sample was characterized by sex, age, and ethnic origin. The following measurements were recorded for each vertebra: (1) the surface area of the VBs and the AE, (2) the midsagittal anterior and posterior length of the AE, (3) the ratios between the AE and VB surface areas, and (4) the ratios between the superior and inferior disc surface areas.

Results: The study revealed that the AE and VBs in men were larger than in women. With age, the AE and VBs became larger; the ratio between the AE and VB surface was approximately 0.5 throughout the middle to lower cervical spine. The ratio of superior to inferior VBs was approximately 0.8. We found no differences between African Americans versus European Americans or between the anterior versus the posterior midsagittal length of the AE of the superior and inferior VBs.

Conclusions: The ratios between the superior and inferior VBs are ≥0.8, and the ratio is the same for the entire middle to lower spine. Thus, the ratio between the superior and inferior VBs to the AE is ≥ 0.5. Men had larger AEs and VBs than women did, with both VBs and AEs becoming larger with age. Knowing these relationships are important so that orthopedic surgeons can best correct these issues in young patients (<25 years old) during spine surgery. The data reported here provide, for the first time, all the relevant sizes of the AE and VB. In future studies, AEs and VBs of living patients can be measured with computed tomography.

Clinical significance: The ER location and function are clinically significant showing any changes during life that might lead to clinical issues related to intervertebral discs such as intervertebral disc asymmetry, disc herniation, nerve pressure, cervical osteophytes and neck pain.

Keywords: African American; Aging; Annular epiphysis; Cervical spine; European American; Vertebral body.