Probably the most common developmental defect reported archaeologically is spina bifida (Roberts and Manchester, 2005: 55). This ‘neural tube defect’ varies in frequency worldwide today, although there are indications that the highest frequencies are found in the British Isles, e.g. 62 of 5607 babies for 1998, and that the lowest frequencies are in Japan, with North America in between (Roberts and Manchester, 2005: 55). Males are more frequently affected than females generally, and genetic and environmental factors are potential causes, these including deficiences in maternal folic acid (vitamin B12), zinc and selenium during foetal development (Roberts and Manchester, 2005: 55).
It is the occulta type, rather than cystica, that is described most frequently (Roberts and Manchester, 2005: 55). Spina bifida occulta is the incomplete fusion of the posterior neural arches of the sacral segments and/or lumbar vertebrae (Roberts and Manchester, 2005: 55). No structures such as the spinal cord protrude out through the space and thus no complications such as infection or paralysis occur (Roberts and Manchester, 2005: 55). In living persons the condition often remains undetected unless X-rays are taken. Spina bifida cystica, on the other hand, is often fatal (Roberts and Manchester, 2005: 55). Three types of severity have been described (Aufderheide and Rodriguez-Martin, 1998: 61):
- meningocele – involves the protrusion of the nerve roots and meninges through the defect, with the spinal cord remaining in the canal and a covering of skin in place,
- myelomeningocele – involves the added protrusion of the spinal cord without normal skin covering,
- myelocele – involves the non-closure of the skin and meninges at the defect, the infection of which usually results in death.
It is unlikely that individuals in the past would have survived such a severe defect, which perhaps explains why there is so little evidence archaeologically (Roberts and Manchester, 2005: 56). If someone did survive, potential complications would include paralysis, incontinence and hydrocephalus (Roberts and Manchester, 2005: 56). For example, a 14-16 year old individual from Florida has been described with spina bifida cystica from lumbar vertebrae 3 to the 2nd sacral vertebrae with subsequent disuse atrophy of some of the bones: this may represent paralysis as a result of the condition (Roberts and Manchester, 2005: 56). More data is available for spina bifida occulta. For the early medieval period in Britain, three sites reporting absolute frequencies (percentage of sacra affected) give frequencies of 8.7% (Roberts and Cox, 2003), while other authors have indicated an average rate of 2.7% for some early British populations (Brothwell and Powers, 1968).
Aufderheide, AC and Rodriguez-Martin, C. 1998. The Cambridge encyclopedia of human palaeopathology. Cambridge: Cambridge University Press.
Brothwell, D and Powers, R. 1968. Congenital malformations of the skeleton in earlier man, pp 173 – 203. In DR Brothwell (ed) Skeletal biology of earlier human populations. Symposia of the Society for the study of Human Biology Volume 8. London: Pergamon Press.
Roberts, C and Cox, M. 2003. Health and disease in Britain: prehistory to the present day. Stroud: Sutton Publishing.
Roberts, C and Manchester, K. 2005. The Archaeology of Disease. Third Edition. Stroud: Sutton Publishing