Introduction: Capasso’s method(CM) has been described in orthopaedic textbooks to be the most sensitive tool for measuring Cobb angle in scoliosis. This method based on “bi-univocal principle” views the scoliosis curve to be an arc of circumference, to be a true reflection of angular values and hence geometrically more valid. However there is no comparative study between the established measurement tools i.e. Oxford cobbometer(OC) & Traditional protractor(TP) vs. CM. Our objectives were to to evaluate the sensitivity of CM against OC & TP in scoliosis and to determine intra & inter-observer reliability of the three methods.

Methods: Three independent blinded observers measured 24 digital AP radiographs of scoliosis on three separate occasions one week apart by CM, OC & TP. The three sets of readings obtained were statistically analysed for intra-observer (Cronbach’s alpha) & inter-observer [Inter-class correlation coefficient(ICC)] reliability.

Results: The mean Cobb angle measured by OC was 42.4(r13-91), by TP was 45.1(r16-89) and by CM was 70.4(r 20-148). The cronbach’s was 0.94 for OC, 0.91 for TP & 0.88 for CM. The ICC was 0.96 for OC, 0.90 for TP & 0.71 for CM. The measurements obtained by CM were higher than the other two methods for all magnitudes of the curves.

Conclusion: CM based on sound geometric principles is perceived to be superior to Cobb angle and has reasonable correlation(Pearson’s®=0.74) with it. However CM overestimates the magnitude of scoliosis as compared to other standard measurement tools. Management decisions based on CM would be inappropriate by current guidelines.

Ethics approval: Not applicable Interest Statement: None

Introduction: Ronald McRae’s textbook clinical orthopaedic examination mentions “Capasso’s method. 1. of evaluation of coronal plane deformity to be the most sensitive tool of measuring cobb angle. However there is no study to date evaluating/comparing this method against popular & widely used tools viz. cobbometer and traditional protractor. Objectives: To evaluate Capasso’s method against commonly used measurement aids w.r.t measurement of cobb angle in scoliosis. Summary of background data: Studies of Cobb method of measurement have multiple sources of error and intra & inter-observer variability. The Capasso’s method which is based on “bi-uni-vocal principle” views the scoliosis curve to be an arc of circumference and to be a true reflection of angular values and hence geometrically more valid. Methods: 24 scoliosis curves were measured by three different examiners on three separate occasions one week apart by 1) Capasso’s method 2) Cobbometer and 3) Traditional protractor on same set of hard copies of digital x-rays. The three set of Cobb angle readings obtained were statistically analysed for intra & inter-observer reliability and assessed for agreement between the three methods of clinical measurement. Results: The mean intra observer variability for protractor, cobbometer & Capasso’s methods were 8.50, 5.50 10.00 respectively. The cobb angle readings obtained by Capas-so’s method was higher than the other two methods for all magnitudes of the curves (< 300, 300–600 & > 600) and was more than two times the conventional readings for curves < 300. The disagreement between Capasso’s method with either of the other two methods (cobbometer & protractor) was statistically significant (p< 0.01). Discussion: This study demonstrates that Capasso’s method significantly overestimates the magnitude of scoliotic deformity esp. for curves < 300 as compared to other existing popular measurement tools. Surgical decision making if were to be based on it would invite criticism and wrath. The present existing methods have their own limitations and the need of the day is a simple three dimensional measuring system to accurately define the magnitude of the deformity