Spondylolysis and spondylolisthesis: A cost of being an erect biped or a clever adaptation?

Abstract

Spondylolysis refers to a separation in a vertebral arch between the body and the spinous process. Most spondylolysis seen in humans occurs in the lower lumbar region and is due to stress (fatigue) fracturing, usually through the isthmus between the superior and inferior articular processes. Referred to here as “typical” spondylolysis, it is related to erect posture and bipedal locomotion, and, as such, it is a uniquely hominid condition. It develops only after a child has begun to walk, and a developing lesion may heal or progress to complete separation. Seen more often in males than females, frequencies among populations vary widely. Certain activities have been suggested to put individuals performing them at greater risk to develop the condition. Although often approached as a pathological condition requiring corrective treatment, spondylolysis usually produces relatively mild symptoms if any at all, and may even provide the advantages of greater lower back flexibility. Complete bilateral spondylolysis separates the inferior articular processes from the body, thus allowing the body to slip forward relative to the vertebra below (spondylolisthesis). Another form of the condition, referred to as degenerative spondylolisthesis, allows a slow forward migration of one vertebra over another due to osteoarthritic remodeling of the posterior vertebral joints without any spondylolysis. © 1996 Wiley-Liss, Inc.