The neuromechanics of idiopathic scoliosis is about the changes in the bones, muscles and joints in cases of spinal deformity consisting of a lateral curvature scoliosis and a rotation of the vertebrae within the curve, that is not explained by either congenital vertebral abnormalities, or neuromuscular disorders such as muscular dystrophy. The idiopathic scoliosis accounts for 80–90% of scoliosis cases. Its pathogenesis is unknown. However, changes in the vestibular system, a lateral shift of the hand representation and abnormal variability of erector spinae motor map location in the motor cortex may be involved in this disease. A short spinal cord and associated nerve tensions has been proposed as a cause and model for idiopathic scoliosis. Besides idiopathic scoliosis being more frequent in certain families, it is suspected to be transmitted via autosomal dominant inheritance. Estrogens could also play a crucial part in the progression of idiopathic scoliosis through their roles in bone formation, growth, maturation and turnover. Finally, collagen, intervertebral disc and muscle abnormalities have been suggested as the cause in idiopathic scoliosis, although these are perhaps results rather than causes.
Demographic data
The patient's age at presentation of scoliosis, the remaining growth, the menarche status and the magnitude of the curve are used to foresee the idiopathic scoliosis curve progression. However, the relative importance of each factor and how they may interact is not clearly defined. The earlier the scoliosis appears, the more likely it will progress. Though it is recommended that idiopathic scoliotic people should practice a sport for aerobic exercise and development of a positive body image, practice of a sport at a competitive level is to be avoided.
Age
Idiopathic scoliosis can appear at different ages. Infantile idiopathic scoliosis that appear from the birth to 3 years old, account for 0.5% of idiopathic scoliosis. Juvenile idiopathic scoliosis that appear from the 4 to 10 years old, account for 10.5% of idiopathic scoliosis. Adolescent idiopathic scoliosis that appear after the age of 10 years, account for 89% of idiopathic scoliosis. From these statistics, it seems that individuals are at highest risk of developing idiopathic scoliosis during adolescence.
Physical activity level
Because scoliotic people have higher joint laxity compared to non-scoliotic people, they are drawn toward gymnastics but the practice of gymnastics for less than 20 hours training per week does not cause scoliosis. Based on populations that had more than 20 hours training per week, idiopathic scoliosis has been observed among 10% of tennis players, 16% of young swimmers and 24% in professional ballet companies. The exposure of the body to high repetitive mechanical constraints may influence the occurrence of idiopathic scoliosis.
Physiology
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 vertebral column can be deformed at the thoracic level, at the lumbar level or at both. In the lumbar region, scoliosis induces perturbations to standing balance. The thoracic region is the location that most impacts movement strategies. Scoliosis impedes on the movement of the ribs, places the respiratory muscles at a mechanical disadvantage and displaces the various organs of the thoracic cavity.
Skeleton
In a scoliotic patient, the vertebral column experiences extension forces on the convex side and compression forces on the concave side. At the apical vertebra, average bone density for the concave cortical bone is higher than for the convex cortical bone, and cancellous bone density is higher for the concave side than for the convex side. The concave side of a vertebra is less porous and has a thicker cortical bone than the convex side, which is consistent with Wolff's law about bone remodeling.