Paraspinal muscle pathology in experimental scoliosis.

Paraspinal muscle biopsies from ten rabbits with experimentally induced scoliosis and from four healthy controls were analyzed histologically and histochemically. Scoliosis was induced by two different methods: six animals underwent unilateral damage of the dorsal column of the spinal cord (mean curve: 22 degrees) and four costotransversectomy (mean curve: 47 degrees). In eight scoliotic animals myopathic changes were detected on the muscles of the concave side. Only those animals which underwent costotransversectomy showed a neuropathic pattern with cronic denervation changes on the convex side. As regards the fiber type distribution, the control group showed a higher percentage of type-I fibers, which were similar on both sides of the spinal cord. No fiber proportion asymmetry could be detected in the muscles on the concave side in normal or scoliotic rabbits. There was a tendency to depart from normal values, in two different ways, on the convex side of scoliotic animals. Thus, in contrast to the medullary damage group, the muscles of the costotransversectomized rabbits showed an increased proportion of type-I fibers. Taken together, our findings support the hypothesis that myopathic changes as observed in human idiopathic scoliosis are a consequence of the postural deformity. Fiber type distribution does not appear to be related to the curvature in the same way.