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

Abstract

Background The Cobb angle measurement is well established for the measurement of coronal deformity 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 scoliosis 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°u sing 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°r otation 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 error rotation of ?45°). Conclusion The influence of rotational misplacement of the patient 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 patient toward the apex of the scoliosis falsely decreases the Cobb angle.

Characterizing the differences between the 2D and 3D measurements of spine in adolescent idiopathic scoliosis

“…In the 2D X-ray measurements the vertebral endplates or the diameter of the oval shape presenting the endplate is projected on the X-ray projection planes. This technique was shown to be prone to error as the scoliotic curve was rotated with respect to the scanner [23]. In line with these results we showed that the differences between the 2D and 3D techniques increased as the pelvic axial rotation and apical vertebrae rotation increased ( Table 2).…”

Evaluation of a computer-aided method for measuring the Cobb angle on chest X-rays

“…The diagnosis and treatment of scoliosis rely on the severity of the spinal deformity and the risk of progression [3]. Currently, the Cobb angle is an objective radiographic parameter to quantify the severity of scoliosis on coronal radiographs [4]. A Cobb angle > 10° is considered clinically significant for scoliosis diagnosis [5], whereas the variability of Cobb angle measurements has been reported to range from 3° to 10° in previous studies [6].…”

Proper positioning of mice for Cobb angle radiographic measurements

“…(20,21) The diagnosis and management decision of scoliosis relies on the Cobb angle measurement and thus these measurements must be accurate and consistent. The measurement error for human subjects has already been exempli ed from various aspects (5,8,(22)(23)(24). However the effects of mouse positioning on angle measurement is unclear.…”

“…(6, 7) A cut-off of 5° is often used to identify signi cant changes in the curve. (8) Scoliosis animal models are necessary for establishing and testing mechanical and genetic etiologies.…”