Deltoid pathology in idiopathic scoliosis.

Histographic analyses of deltoid, trapezius, and quadriceps muscles have been performed in patients with scoliosis of different kinds and in nonscoliotic controls. The results point towards specific pathology in the deltoids, especially on the concave side of the curvature in idiopathic scoliosis. The pathology consists of an overall fiber "hypotrophy" and a type 1 area decrease, often with frank atrophy. Electromyographic examination confirmed the deltoid pathology, showing a myopathic pattern in all the concave-side deltoids and often in the convex ones as well. The cause of the cephalocaudal and side-to-side asymmetry is possibly connected to developmental and neurotrophic factors that may be operative in the complex etiology of the disease.