The detection of spinal deformities through the various screening programs is a challenging issue. Initially the forward bending test and later the use of back shape analysis methods, such as scoliometer and Moire topography were followed by an increased number of false positive results and an increased number of referrals and unnecessary radiographs . The more advanced 3-D computer assisted systems and the various body scanners are quantifying more accurately the surface morphology of the trunk and efforts have been made to correlate these findings with the spinal deformity.
The present study shows that in younger children the concordance of the surface and spinal deformity is weak and it becomes stronger as the children are growing up. Therefore, in younger children with surface trunk asymmetry, the prediction of the spinal deformity alone from the surface topography is inaccurate, simply because surface topography reveals the thoracic cage and the spinal deformity together. Furthermore the Cobb angle alone cannot explain the whole of the surface deformity . Fourteen out of 83 girls (16.9%) in our study had straight spines, although the scoliometer readings were ≥ 7°. When adding the 7 girls with spinal curves <10°, it is interesting that 21 girls (25%) with an ATI ≥7° had a spinal curve under 10° or had a straight spine.
The rib-index clearly demonstrates the thoracic cage deformity and when its value is above 1, it displays the existence of surface asymmetry, which is the main indicator for referral during school screening for scoliosis . The rib-index is a radiological sign and thus it is not obtainable by the screening programs, but is more meaningful when studying the correlation between the surface and the spinal deformity.
The role of the rib cage in the pathogenesis of idiopathic scoliosis has been implicated in the past [21–27].
The growth of the thoracic spine and the growth of the rib cage are directly related and that a growth disturbance of one induces deformity in the other . Either unilateral rib or spine tethering produces both a scoliosis and rib cage deformity . The deformity induced by unilaterally tethering the ribs is much greater than the deformity induced by unilaterally tethering the transverse processes of the spine. This may be a consequence of the longer moment arm provided by the ribs, thereby producing a larger bending moment to deform the thoracic spine .
The spine and ribs work together efficiently at respiration as a dynamic biomechanical structure only under specific conditions . When the thorax is affected by significant deformity, the dynamics of this system change, interfering with normal respiration and lung development . Sevastik et al induced scoliosis experimentally in young New Zealand rabbits either by performing rib osteotomies and interposing a metallic ring into the osteotomy gap to asymmetrically elongate the ribs or by unilaterally segmenting three intercostal nerves [31, 32]. In addition, abnormalities in the evolution of anterior chest wall blood supply were implicated in the pathogenesis of progressive right-convex female thoracic scoliosis . On the contrary, young children suffering thoracic insufficiency syndrome and undergoing spine fusion for scoliosis may continue to develop significant thoracic hypoplasia, restrictive lung disease and respiratory insufficiency by early adulthood with early death . A clearer understanding of this reciprocal association between the growth of the rib cage and the thoracic spine has never been quantified. The findings of the present study, which includes mild scoliotic curves, correlate the growth of the rib cage and the thoracic spinal deformity, supporting the hypothesis that the rib cage deformity precedes the spinal deformity in the pathogenesis of idiopathic scoliosis, but can not exclude that pathogenesis might be in the vertebral column.
Age is a very important factor and has a definite effect, since it influences the correlation between the surface and the spinal deformity. In younger children this correlation is very weak, while it is stronger in older children. This important finding of the existence of remarkable rib cage deformity without simultaneous spinal deformity in younger school screening referrals requires further research. A longitudinal study ought to be conducted to discriminate the percentage of children that will in time develop scoliosis and the possible responsible factors.
As a result of the effect of growth on the correlation between the thoracic surface deformity and the spinal deformity, the predictive value of the existing formulas which calculate the Cobb angle from surface measurements is poor. Therefore our recommendation is to take into consideration the effect of growth when developing such predictive models, otherwise they can be inaccurate.
One more interesting outcome from this study is that screening younger children for scoliosis is beneficial, at least for the purpose of scoliosis aetiology research. This study could not be completed and the above findings couldn't be resulted unless younger children were screened in our scoliosis school screening program.
These findings may also have implications for the conservative treatment in younger scoliotics with braces when indicated. The correction of the more pronounced rib cage deformity which is addressed by the brace could easily prevent the deterioration of the less deformed "central axis" that is the spinal column at an earlier stage.
In conclusion growth seems to have a significant effect in the correlation between the rib cage and the spinal deformity in girls with IS. The findings of the present study support the hypothesis that the correlation between thoracic surface and spinal deformity is weak in younger children, implicating that the thoracic cage deformity precedes that of the spine in the pathogenesis of idiopathic scoliosis.