Moderate Interrater and Substantial Intrarater Reproducibility of the Roussouly Classification System in Patients With Adult Spinal Deformity

Study Design: Reproducibility study of a classification system. Objectives: To provide the inter- and intrarater reproducibility of the Roussouly Classification System in a single-center prospective cohort of patients referred for Adult Spinal Deformity. Summary of Background Data: The Roussouly Classification System was developed to describe the variation in sagittal spine shape in normal individuals. A recent study suggests that patients’ spine types could influence the outcome following spinal surgery. The utility of a classification system depends largely on its reproducibility. Methods: Sixty-four consecutive patients were included in a blinded test-retest setting using digital radiographs. All ratings were performed by four spine surgeons with different levels of experience. There was a 14-day interval between the two reading sessions. Inter- and intrarater reproducibility was calculated using Fleiss Kappa and crude agreement percentages. Results: We found moderate interrater (? = 0.60) and substantial intrarater (? = 0.68) reproducibility. All 4 raters agreed on the Roussouly type in 47% of the cases. The most experienced rater had significantly higher intrarater reliability compared to the least experienced rater (? = 0.57 vs 0.78). The two most experienced raters also had the highest crude agreement percentage (75%); however, they also had a significant difference in distribution of spine types. Conclusion: The current study presents moderate interrater and substantial intrarater reliability of the Roussouly Classification System. These findings are acceptable and comparable to previous results of reproducibility for a classification system in patients with Adult Spinal Deformity. Additional studies are requested to validate these findings as well as to further investigate the impact of the classification system on outcome following surgery.