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Spina Bifida in Prehistoric Tennesseans

by Maria O. Smith, Department of Anthropology, Northern Illinois University, and Research Associate, McClung Museum of Natural History & Culture

The typical human spine is composed of twenty-four individual bones and five or so fused vertebrae at the caudal, or tailbone, end (the sacrum). The spine functions to support our body weight and to enclose and protect the spinal cord. The most common of all birth defects, spina bifida is the failure of the bones of the vertebral column to enclose the spinal cord. This defect ranges from an exposed and protruding spinal cord, which is severely debilitating and often fatal, to a normal cord which lacks the bony enclosure at one or several locations. This latter form of spina bifida, referred to as spina bifida occulta, is benign and presents no symptoms.

East Tennessee has an unusually high frequency of births with the severe form of spina bifida. This inexplicable pattern prompted my examination of the pattern and frequency of spina bifida among the prehistoric inhabitants of Tennessee. The examination focused on the less severe form, spina bifida occulta, which occurs most frequently in the sacrum and the lower spine. Since survivorship is better for this form, I was able to compare and contrast frequencies between different prehistoric populations, using the McClung Museum skeletal collections.

Nutritional deficiencies have been observed to be among predisposing factors in the occurrence of spina bifida. With this in mind, I compared two prehistoric Tennessee samples of contrasting nutritional status — a hunter-gatherer sample (Middle to Late Archaic cultures, ca. 5000-1500 BC) and a maize agriculturalist sample (Late Mississippian cultures, ca. AD 1300-1600). Because of their reliance on maize as the primary food, maize agriculturalists are demonstrably more nutritionally stressed than hunter-gatherers, who consume a wide variety of plant and animal foods. Predictably, the maize agriculturalists sample yielded the only sacra showing totally exposed spinal cords and a higher frequency of sacra indicating partially exposed spinal cords. These results strongly argue for a mediating influence of nutrition in the expression of spinal abnormalities. Continued examination of spinal cord abnormalities in these collections should yield more data on this topic.

Preliminary results of this research were presented at the Society for Research into Hydrocephalus and Spina Bifida 1990 annual meeting in Oviedo, Spain.