BACKGROUND: The Cobb angle measurement is well established for the measurement of @entity85 aspect of scoliotic curves. The effect of positional differences in relation to the apex side of the scoliosis is not yet fully quantified. While theoretically plausible that positioning error with rotation toward the apex of the @entity1635 would decrease the Cobb angle, the relations are not investigated yet and were object of this study. MATERIALS AND METHODS: Multiple measurements of the Cobb angle were performed, while turning a spine-pelvic cadaveric specimen with a right-sided thoracic scoliosis of 47   (in neutral position) from 45   to -45   in steps of 5   using biplanar radiography. Statistical methods were applied to find the critical position, in which measurement errors potentially become clinically relevant (Cobb angle deviation >5  ). RESULTS: Turning the specimen to the right (toward the apex of the scoliosis) produced during the first -15   of rotation, a Cobb angle ranging from 47   to 45  . At -20  , the Cobb angle was 42  , at -25   rotation 37   and at -30   rotation 36  . Above -30   rotation, the measured Cobb angle decreased to 36   (77  % of the original Cobb angle). No relevant differences were found by rotating the specimen to the left (away from the apex) (47   at neutral rotation and 44   at maximal @entity717 of +45  ). CONCLUSION: The influence of rotational misplacement of the @entity1 at the time of image acquisition on Cobb angle measurements is negligible for a rotational misplacement of   20   of rotation for a idiopathic right-sided thoracic scoliosis of 47  . Over 20   of rotational misplacement of the @entity1 toward the apex of the @entity1635 falsely decreases the Cobb angle.

Radiographic measurement error of the scoliotic curve angle depending on positioning of the XXXX and the side of scoliotic curve.

@entity1 :: ('9606', 'Species') :: ['patient'] @entity717 :: ('MESH:D009069', 'Disease') :: ['error rotation'] @entity85 :: ('MESH:D009140', 'Disease') :: ['coronal deformity'] @entity1635 :: ('MESH:D012600', 'Disease') :: ['scoliosis']
@entity1 :: (9606,Species) :: ['patient']
