Abstract
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
Correspondence should be addressed to BSS c/o BOA, at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London, WC2A 3PE, England.
