The epiphyseal ring: A long forgotten anatomical structure with significant physiological function

Study Design.: A descriptive study of the epiphyseal ring's structural design along the thoracolumbar spine. Objective.: To characterize and analyze the shape and size of the epiphyseal ring, to better understand its function. Summary of Background Data.: The literature is lacking in metrical data pertaining to the epiphyseal ring that is usually described as a narrow bony labrum on which the external fibers of the anulus fibrosus are anchored. Most researchers express doubts as to whether the term epiphysis is justified in this case. Methods.: The sample studied included 240 human skeletons (vertebrae T4-L5) from a normal adult population (divided by sex, ethnicity, and age). Measurements of the vertebral body and epiphyseal ring were taken using a digital caliper at four different locations: anterior, posterior, right, left. In addition, each vertebral surface was photographed and the epiphyseal ring area measured (using image analyzer software Image J). Results.: We found that relative to vertebral body size throughout the thoracolumbar spine, the anterior section of the ring was the widest and the posterior section the narrowest. The lateral parts presented intermediate values. Relative to the discal area, the epiphyseal ring area gradually decreased from T7 to T12 and increased from T12 to L4. The area of the inferior ring was always larger than the superior ring (significant only for lumbar vertebrae), regardless of sex, ethnicity, and age. Conclusion.: The epiphyseal ring varies largely in size and shape along the thoracolumbar spine. Much of its metrical properties are dictated by the applied mechanical stress regime during various movements, and/or the general anatomic structure of the spine.