Comparative Radiological Study of the Spines of a Primitive Population with North Americans and Northern Europeans.

The gradual development of malfunction in the intervertebral disc and its subsequent degeneration, was demonstrated by Hansen (1959), who, in a study of the pathogenesis of disc degeneration in animals, outlined a process that appears to have close parallels in the human. He demonstrated in dissected specimens that degenerative change begins at the end of growth and is characterised by a slow change of the nucleus from a plastic amorphous state to a less plastic, fibrocartilaginous one. At the same time the nucleus loses some of its water content, and as hyaluronic acid becomes sulphated to chondroitin sulphate and other polysaccharides the disc becomes firmer, and its function is disturbed as more mechanical strain is taken on the annulus, this process occurring in all discs. On investigation of the spines of horses, cows, dogs, camels and giraffes Hansen found that degeneration with narrowed disc space and hypertrophic change only occurred at levels where mechanical strain was greatest. In the camel and giraffe these changes are found in the cervico-thoracic region ; in the basset hound and dachshund dog they occur in the lower thoracic level, which is the central point of sag of the spine. In bovine animals this change is found in the Iumbo-sacral area, which is the level where about 50 per cent of spinal movement occurs. In the human the relationship between degeneration and heavy labour was demonstrated by Hult (1954) and by Kellgren and Lawrence (1958). Hult showed a parallel increase of degeneration with heavy labour. Kellgren and Lawrence showed that coal miners had a greater incidence of degenerative change than their neighbours. The susceptibility of discs at particular levels to degeneration and the relationship of particular types of movement are more difficult to demonstrate. The quadrupeds studied by Hansen are not representative ofall quadrupeds but of selected mammals in which a particular type of spinal mechanism concentrates forces at one point. In bovine animals most movements occur about one disc. In achondroplastic dogs the strain is focused on the apex of the lordosis of a sagging spine. In the camel and giraffe it is likely that maximum strain and a consistent lordosis focus the strain on a very few discs, suggesting that trauma at the point of maximum load is the cause of these changes. Quadrupedal stance, however, is not the most important factor. Hansen had no primates in his series and the range of spinal movement in these animals suggests that factors that he described would not be found. In man there is a difference from the other primates in his erect stance, having a less efficient S-shaped curve to his back instead of a gentle C-shaped curve. This produces three areas of concentration of strain : at the apices of the cervical, thoracic and lumbar curves, which correspond roughly to the areas of degenerative change, particularly so in the lumbar spine. The posture of humans can be divided into squatters and non-squatters. In searching, like Hansen, for a constant traumatic factor in the cause of disc degeneration we made a comparative study of the two groups. American and Swedish radiographic studies were compared with studies of a tribe of jungle dwellers, a squatting tribe in West Central India.