Assessment of early rib hump deformity correction in adolescent idiopathic scoliosis treated with a dynamic derotation brace using the double rib contour sign

The rib index is not practically affected by the distance between the radiation source and the examined child

Background

All lateral spinal radiographs in idiopathic scoliosis (IS) show a Double Rib Contour Sign (DRCS) of the thoracic cage, a radiographic expression of the rib hump. The outline of the convex overlies the contour of the concave ribs. The rib index (RI) method was extracted from the DRCS to evaluate rib hump deformity in IS patients. The RI was calculated by the ratio of spine distances d1/d2 where d1 is the distance between the most extended point of the most extending rib contour and the posterior margin of the corresponding vertebra on the lateral scoliosis films, while d2 is the distance from the least projection rib contour and the posterior margin of the same vertebra, (Grivas et al 2002). In a symmetric thorax the “rib index” is 1.

This report is the validity study of DRCS, ie how the rib index is affected by the distance between the radiation source and the irradiated child.

Methods

The American College of Radiology's (2009) guidelines for obtaining radiographs for scoliosis in children recommends for the scoliotic - films distance to be 1,80 meters.

Normal values used for the transverse diameter of the ribcage in children aged 6-12 years were those reported by Grivas in 1988.

Results

Using the Euclidean geometry, it is shown that in a normal 12-year old child d1/d2 = 1.073 provided that the distance ΔZ ≈ 12cm (11,84) and EA = 180cm, with transverse ribcage diameter of the child 22 cm.

Conclusions

This validity study demonstrates that the DRCS is substantially true and the RI is not practically affected by the distance between the radiation source and the irradiated child. The RI is valid and may be used to evaluate the effect of surgical or conservative treatment on the rib cage deformity (hump) in children with IS. It is noted that RI is a simple method and a safe reproducible way to assess the rib hump deformity based on lateral radiographs, without the need for any other special radiographs and exposure to additional radiation.

Letter to the editor concerning: "a comprehensive review of thoracic deformity parameters in scoliosis" by Jonathan A. Harris, Oscar H. Mayer, Suken A. Shah, Robert M. Campbell Jr., Sriram Balasubramanian. Eur Spine J (2014) 23:2594-2602, DOI 10.1007/s00586-014-3580-8

In this letter to the Editor, an additional radiological thoracic deformity parameter is described, which was not included in the review, namely the rib index (RI). The index and its usefulness of its application are described, both in the clinical praxis and in the aetiology of idiopathic scoliosis. The pertinent literature is also sited.

Rib index

This article analyzes the double rib contour sign (DRCS) and the rib index (RI). The analyzed topics are 1. the history of presentations - publication of DRCS-RI, 2. the study source origin: school screening for idiopathic scoliosis (IS), 3. what the DRCS and the RI are- Description, 4. the quantification of the DRCS - RI, 5. a reliability study for RI 6. how much the rib index is affected by the distance between the radiation source and the irradiated individual, 7. the implications on IS aetiology, 8. the applications of Rib index for a. documentation of the deformity, b. assessment of physiotherapy, c. assessment of brace treatment and d. pre- and post-operative assessment; assessment of the rib-cage deformity correction on the transverse plane, 9. the use of RI and implications for screening policies 10. the reference of the RI method in spinal textbooks and finally 11. the citations in Google Scholar.

The pendulum swings back to scoliosis screening: screening policies for early detection and treatment of idiopathic scoliosis - current concepts and recommendations

This editorial article initiates the school scoliosis screening thematic series of the Scoliosis journal. The various issues on screening policies are discussed; clinical and practical recommendations of setting up school screening programs are also described.