Reliability of a Novel Cobb Protractor for Measuring the Cobb Angle of Radiograph in Scoliosis

OBJECTIVE: To introduce a novel Cobb protractor and assess its reliability and rapidity for measuring Cobb angle in scoliosis patients. METHODS: The novel Cobb protractor had two endplate markers. A measurement was performed just to align the two markers to each endplate of the curve. The Cobb angle on the posteroanterior radiographs of 24 patients clinically diagnosed with adolescent idiopathic scoliosis was measured by three orthopedic surgeons with both standard Cobb method and the new technique, and the time of measurement was recorded. Intraclass correlation coefficients (ICCs) were calculated to assess the reliability of the new method. RESULTS: The time for a measurement with the new tool was approximately 10 seconds less than the time that used to finish a measurement with the standard method (P<0.05). The overall mean Cobb angle for the major curve of the 24 patients was 47.8°. The mean overall intraobserver and interobserver ICC was 0.971 and 0.971 for the Cobb method group, while the overall intraobserver ICC and the interobserver was 0.985 and 0.979 for the new tool group. CONCLUSIONS: The novel Cobb protractor could perform quick measurement and measure almost all forms of radiographs. The Cobb protractor might be an ideal instrument to measure the Cobb angle.