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.

Spondylolysis in Inuit skeletons from Arctic Canada

“…Although familial patterns of occurrence of the condition have occasionally been noted and genetic models have been hypothesized (Merbs, 1996a), what exactly may be inherited has never been established. Clearly it is not the defect itself.…”

“…Spondylolysis above the thoracic spine is rare, and nearly all cases reported in the clinical literature deal with cervical vertebrae (Merbs, 1996a). The defect commonly involves a pedicle and is attributed to developmental error.…”

“…Although the early argument as to whether spondylolysis represented a developmental defect or was produced by trauma has been largely resolved (Merbs, 1996a), some important aetiologic questions remain. The classic picture of spondylolysis is complete separation (lysis) through pars interarticularis (the isthmus between the superior and inferior articular processes), and the vertebrae most commonly affected are the lower lumbar, especially L5.…”

“…Classic lower lumbar spondylolysis appears to be a uniquely human phenomenon, intimately related to the lumbar curve and the erect posture that it permits (Merbs, 1996a). Rare examples of spondylolysis in animals other than humans have been reported, but they appear limited to congenital errors, as in some non-human primates (Schultz, 1972), or stress patterns unrelated to erect posture, as in Thoroughbred racehorses (Haussler & Stover, 1998).…”

“…The incidence of the condition appears to vary considerably from group to group and through time, with frequencies of less than 5% to over 50% having been recorded (Stewart, 1931;Merbs, 1996a). Very ancient cases have been reported for 4,000 year old maritime archaic skeletons from Port au Choix, Newfoundland, Canada (Anderson, 1976), and a 3,000-4,000 year old La Jollan woman from Punta Minitas, Baja California, Mexico (Merbs, 1980).…”