Expressing Cobb Angle as Linear Measurement in Scoliosis and Its Significance: A Clinical and Geometrical Analysis of Scoliosis.

OBJECTIVE: The aim of this study was to formulate an objective clinical and geometric relationship between Cobb angle and the difference between the lengths of convex and concave sides (convexo-concave vertebral difference) of the structural curve in scoliosis. Is it possible to express Cobb angle in such a way that it could be visualized as a length, especially while planning for surgical correction of scoliosis?

METHODS: Thirty consecutive patients below the age of 19 years with a scoliosis of Cobb angle more than 10 degrees were included in the study. Convexo-concave vertebral difference of the structural curve was measured. Its relationship with the measure of Cobb angle was studied.

RESULTS: Author obtained a significant linear correlation between the convexo-concave vertebral differences and the Cobb angle. Using the formula Y=2d.Sin (X/2) the convexo-concave vertebral difference could be predicted. The difference thus obtained gives a quantitative measure of the maximum length of correction possible in the structural curve.

CONCLUSION: It is possible to express the Cobb angle as a function of linear measurement. The author proposes that this would aid the surgeons to accurately and predictably achieve the desired scoliosis correction.