Trunk muscle myoelectric activities in idiopathic scoliosis.

Twenty adolescent girls with mild-to-moderate cases of idiopathic scoliosis and twelve adolescent girls with structurally normal spines performed 15 exercises isometrically while standing. The exercises included resisting flexion, extension, and lateral bending moments imposed on the trunk. Myoelectric activities in 12 trunk muscle groups were measured during these performances, using surface electrodes. For one set of comparisons, the patients were divided into those whose clinical records documented curve progression and those with no documented progression. No significant differences were noted in mean myoelectric activities between these two patient groups. For a second set of comparisons, the subjects were divided into patients with curves of more than 25 degrees, patients with curves of 25 or fewer degrees and normals. No significant differences in mean myoelectric activities were noted between the patients with the smaller curves, while the patients with the larger curves had significantly larger convex side myoelectric activities in their anterior, lateral and posterior muscles at lumbar levels compared to the normal girls. The findings of this study, along with biomechanical model analyses, suggest that the asymmetries in muscle actions evidenced by myoelectric measurements result from scoliosis. Scoliosis progression seems not to be caused by asymmetry in muscle contractions; rather it may be caused by a lack of adequate asymmetry.