The reliability and diagnostic value of radiographic criteria in sagittal spine deformities: comparison of the vertebral wedge ratio to the segmental cobb angle

Abstract

Study design: A prospective, radiographic cohort study.

Objectives: This study assessed the radiographic reliability and diagnostic value of the vertebral wedge ratio (WR) to the more segmental Cobb angle (CA) regarding sagittal spine deformities.

Summary of background data: The use of the CA has been used to assist in the radiographic diagnosis of various sagittal spine deformities. However, the reliability and diagnostic aptitude of the CA remains speculative and may not be as receptive to individual variations of vertebral integrity in sagittal spine deformities.

Methods: Sixty patients (age range, 8-21 years) who were diagnosed with Scheuermann's kyphosis (Group 1; n = 16), with postural roundback (Group 2; n = 23), or who were regarded normal (Group 3; n = 21) were radiographically evaluated to assess the reliability and diagnostic potential of the vertebral WR (apex of the curve and 2 adjacent vertebrae) and segmental CA. Radiographic assessment was conducted by 3 independent blinded observers on 3 separate occasions.

Results: Very strong intraobserver (WR a = 0.85-0.99; CA a = 0.97-0.99) and interobserver (WR a = 0.79-0.89; CA a = 0.95) reliabilities were noted. A greater degree of WR reliability was noted in Group 1, whereas CA reliability remained consistent in all Groups. A statistically significant difference was found between all Groups in relation to vertebral WR and segmental CA (P < 0.05). Based on relative risk ratio analyses, an apex wedge ratio of < or = 0.80 and/or a segmental Cobb angle of > or = 20 degrees is highly and significantly associated with Scheuermann's kyphosis.

Conclusion: The segmental CA exhibited a higher degree of reliability than the vertebral WR. The apex vertebral WR exhibited the greatest amount of wedging in the Scheuermann's patients; whereas in the other groups it remained largely consistent with the adjacent vertebral WRs. An apex vertebral WR < or = 0.80 and/or a segmental CA of > or = 20 degrees are highly associated with the clinical diagnosis of Scheuermann's kyphosis. If the segmental CA cannot be ascertained, the apex vertebral WR is a relatively strong reliable alternative, primarily with regards to Scheuermann's kyphosis. In addition, the type of deformity may potentially dictate the ideal measuring method.