Morphometry and pathology of the paraspinous muscles in idiopathic scoliosis.

Muscle biopsies from the apex of both sides of the curve of 31 patients with idiopathic scoliosis showed abnormalities in fiber-type distribution in 68 per cent and in fiber size in 55 per cent. There was no preference for either side. Type 1 fiber predominance was as common as type 1 fiber deficiency. Atrophy occurred in 33 per cent and affected mainly type 1 fibers: atrophy of type 2 fibers was rare. Hypertrophy was limited to type 2 fibers, and occurred in 26 per cent. The strength factor for type 1 fibers exceeded that for type 2. Type 2A fibers were no larger than 2B fibers: there was a large type 2A predominance, more so on the convex side. Most of the muscle changes appear to be secondary and compensatory: none suggests a pathogenesis for the curve.