Spondylolysis of the sacrum in Alaskan and Canadian Inuit skeletons.

Spondylolysis of the lower back, particularly that involving the isthmus between the superior and inferior articular processes (pars interarticularis), is generally attributed to stress fracturing caused by movement of the affected vertebra relative to the vertebra below. The finding of isthmic spondylolysis in the first vertebra of a fused sacrum is thus unusual and requires explanation. Although unrepresented in the clinical literature, sacral spondylolysis has been reported for archaeological specimens and appears to be especially prevalent in North American Inuit. A study of 373 Inuit sacra from Alaska and Canada produced 16 examples of spondylolysis (eight from each area). All but one of the affected individuals were male, and nearly all were young adults, many between 18 and 20 years of age. All cases of sacral spondylolysis observed in this study were judged to have resulted from stress fracturing that occurred while S1 was still unfused, and most appear to have been in the process of healing, following fusion of S1 with S2, when death occurred. The high frequency observed in these people is attributed to unusual stresses becoming concentrated in the lower back of adolescent males due to such activities as weight lifting, wrestling, kayak paddling, and harpooning, combined with, and perhaps even contributing to, delayed maturation (S1-S2 fusion) of the sacrum.