Scoliosis are "captured", meaning that they are held fast between the ilium bones of the pelvis. Compared to humans, Old World monkeys have far larger erector spinae muscles, which are the muscles which hold the spine steady. These factors make the lumbar spine of most primates less flexible and far less likely to deviate than those of humans. While this may explicitly relate only to lumbar scolioses, it is possible that small imbalances in the lumbar spine could precipitate thoracic problems as well. Scoliosis may be a byproduct of strong selection for bipedalism. For a bipedal stance, a highly mobile, elongated
Neuromechanics of idiopathic scoliosis the body to high repetitive mechanical constraints may influence the occurrence of idiopathic scoliosis. Cobb angle is a common measure to classify scoliosis. The greater the angle, the more serious is the disease but the smaller is the number of patients. One to three out of every hundred people have idiopathic scoliosis curves greater than 10° with an equal proportion of boys and girls. One to three out of every thousand people have idiopathic scoliosis curves greater than 30° with a ratio of eight girls for every one boy. Scoliosis is also classified according to the region(s) they affect. The