Comparison of Cobb angle between endplate and pedicle measurement for thoracic adolescent idiopathic scoliosis

English Keywords:Adolescent idiopathic scoliosis  Cobb angle  Endplate  Pedicle  Inter/intraobserver variability

English Abstract:

  【Abstract】 Objectives: To determine and compare the interobserver reproducibility and intraobserver reliability between the pedicle method and the conventional endplate method for measuring the Cobb angle in thoracic adolescent idiopathic scoliosis(AIS). Methods: Fifty-five patients with thoracic adolescent idiopathic scoliosis treated in our clinic from July 2010 to March 2011 were reviewed retrospectively. Standing anteroposterior X-ray film was taken in all patients. The end vertebrae of the major thoracic curve were predetermined by a senior doctor, then three spine surgeons independently examined the radiograms using either endplate method or pedicle method respectively. The results of the Cobb angle were recorded and the rotations of the end vertebrae of the major curve were also evaluated according to the Nash-Moe method. The procedure was repeated one week later. Both intraobserver and interobserver agreements were accessed by calculating the intraclass correlation coefficient (ICCC). The results of the two methods were also compared based on the rotations of the end vertebrae and the curve severity. Results: All ICCC values laid in the excellent or good group for the two methods. For the endplate method, the single ICCC value which indicated intraobserver variability was 0.969 and the average ICCC value representing interobserver variability was 0.900; while for the pedicle method, the single and average ICCC value was 0.972 and 0.880 respectively. While considering the rotation for lower end vertebra using Nash-Moe method, no significant difference was noted for those without rotation (Nash-Moe grade 0)(P>0.05), however, the value measured by pedicle method was significantly smaller than that by endplate method for the rotation of lower end vertebra was prominent (Nash-Moe grade Ⅰ and Ⅱ)(P<0.05). The results measured by pedicle method were significantly smaller than those of the endplate method regardless whether the Cobb angle was more than 25°(P<0.05). Conclusions: Both methods can be used in the practical measurement of thoracic AIS. However, the result by pedicle method is sigificantly smaller than that by the endplate method in patients with prominent rotation of the lower end vertebrae (Nash-Moe grade Ⅰ and Ⅱ), so the endplate method is indicated for measuring the Cobb angle in these patients.