Validity and interobserver agreement of a new radiographic grading system for intervertebral disc degeneration: Part III. Thoracic spine.

PURPOSE: The aim of this study was to assess the validity and objectivity of a new quantitative radiographic grading system for thoracic intervertebral disc degeneration. METHODS: The new grading system involves the measurement variables "Height loss" and "Osteophyte formation", which are determined from lateral radiographs, resulting in the "Overall degree of degeneration" on a four-point scale from 0 (no degeneration) to 3 (severe degeneration). Validation was performed by comparing the radiographic degrees of degeneration of 54 human intervertebral discs to the respective macroscopic degrees, which were defined as the "real" degrees of degeneration. Interobserver agreement was examined using radiographs of 135 human thoracic intervertebral discs. Agreement was quantified by means of quadratically weighted Kappa coefficients with 95% confidence limits (CL). RESULTS: Validation revealed almost perfect agreement between the radiographic and the macroscopic overall degrees of degeneration (Kappa 0.968, CL 0.944-0.991), while the macroscopic grades tended to be underestimated in low degeneration grades. Radiographic grading of two independent observers also exhibited almost perfect agreement (Kappa 0.883, CL 0.824-0.941) as well as tendencies towards rater-dependent differences in low degeneration grades. CONCLUSION: The new quantitative radiographic grading scheme represents a valid, reliable, and almost objective method for assessing the degree of degeneration of individual thoracic intervertebral discs. Potential effects of interindividual variations and the radiographic superimposition of anatomical structures represent a limitation of this method should be taken into account when using the grading system for clinical and experimental purposes, especially with regard to specific morphological as well as patient- and donor-specific characteristics.