Intraobserver and Interobserver Measurement Variability of the Rib-Vertebral Angle Difference.

Background: The rib-vertebral angle (RVAD) differentiates between progressive and resolving infantile idiopathic scoliosis (IIS) curves. Those with a RVAD<20 degrees often resolve without treatment, whereas those >20 degrees often progress and require treatment. The mathematical magnitude of RVAD measurement variability has not been described, and was thus the purpose of this study.