The rib vertebral angle asymmetry in idiopathic, neuromuscular and experimentally induced scoliosis

The concave and convex rib-vertebral angles (RVA) at levels T2 to T12 were measured on AP radiographs of 19 patients with right convex idiopathic thoracic scoliosis, and of ten patients with major thoracic right convex neuromuscular scoliosis. The difference between the angles of the concave and the convex sides, the RVAD, was calculated. The RVA:s were also measured on radiographs from three animal groups where spinal curves bad been induced experimentally: in group I, by selective electrostimulation of a) the latissimus dorsi, b) the erector spinae and c) the intercostal muscles, in 16 rabbits; in group II, by manual bending of the spine of four dead rabbits; and in group III by mechanical elongation of one rib in eight rabbits. In both the idiopathic and the neuromuscular groups, the convex RVA was smaller than the concave RVA between levels T2 and T8, with a maximal difference between T4 to T5. From T9 to T12 the concave RVA was smaller than the convex. With increasing Cobb angle the RVAD:s increased linearly with the greatest difference at the second vertebra above the apex. In the experimental groups the pattern of the RVAD:s between T6 to T12 was similar to the findings of the clinical study. The typical pattern of the RVA:s of the concave and convex side seems to be independent of the underlying cause of the spinal curvature.