The aim of the study is to compare the rib-vertebra angles (RVAs) between children with 10° - 20° of Cobb angle late onset idiopathic scoliosis (LOIS) and non-scoliotic children.

Materials and Method: The RVAs of 47 children, with mean age 12.4 years, who presented LOIS with a Cobb angle 10° - 20°, were studied. The children were classified into three groups according to the site of the scoliotic curve: 17 children had thoracic (T), 14 children had thoracolumbar (TL) and 16 children had lumbar (L) curves. The RVAs of the scoliotic children were compared to the RVAs of 60 non-scoliotic children of a similar age group, who were studied in the past.

Results: The comparison of the right and left RVAs within each group showed that the children who had: T curves differ at the level T4, T5, T6, T7 and T8, TL curves differ at the level T3, and L curves differ at the level T7 and T12.

The comparison of the ipsilateral RVA’s between the scoliotic groups showed that between: T and TL curves there are no differences at any thoracic level, between T and L curves the RVAs differ at the T7 level on the right side, whereas there are no differences between the RVAs on the left side, between TL and L curves the RVAs differ at the level T5, T6, and T7 on the right and at the level T5 on the left side. Comparing the RVAs between the scoliotic and nonscoliotic children, it was apparent that the scoliotic children rib cage had lower RVAs (p<0.0l) at almost all thoracic levels.

Discussion: It has been reported that RVAs is an expression of the resultant muscle forces, which act on each rib. It was also suggested that RVA asymmetries by weakening the spinal rotation-defending system are aetiological for idiopathic scoliosis, (Burwell et al 1992). This study shows that scoliotic children with small curves have underdeveloped thoracic cage compared to nonscoliotic counterparts. The differences are more apparent in the scoliotic children with thoracic curves. It is suggested that the differences of the RVAs between right and left side in this group are an expression of asymmetric muscle forces acting on the thoracic cage. It is concluded that asymmetric muscle forces participate in the pathogenesis of idiopathic scoliosis on the thoracic cage, which deforms early.