Progression of idiopathic scoliosis: an analysis of muscle actions and body weight influences.

The tendencies of lateral curves in the spine to increase were analyzed using biomechanical models. The effects of contractions of the trunk muscles and of use of different strategies to support upper body segment weights in upright positions of the trunk were investigated in model spines with five structurally normal initial configurations and 13 different initial configurations of scoliosis. Forces that represented these trunk muscle contractions and body weight applications were applied to the model spines, and the resulting configurational changes were computed. These changes were then examined to see to what extent altered loads on the spine might plausibly explain lateral curve progression tendencies in idiopathic scoliosis. The study findings suggest that if the progression of idiopathic scoliosis results from trunk neuromuscular system malfunctions, the malfunctions are more likely to be in the neural systems that control trunk muscle contractions and body weight support strategies than in the functional capabilities of the muscles themselves.