Interobserver and Intraobserver Reliability of a Novel Classification System for Distal Radioulnar Joint Instability.

A clinically useful classification system requires precise definitions, reproducibility, and applicability across different levels of clinical experience. Distal radioulnar joint instability remains insufficiently represented in fracture based classifications, contributing to diagnostic uncertainty and variability in treatment strategies. This retrospective observational study assessed the interobserver and intraobserver reliability of a previously proposed classification system for distal radioulnar joint instability. Five orthopedic surgeons, including three board-certified specialists and two final year residents, independently evaluated forty five clinical cases comprising distal radius fractures, Galeazzi fractures, and Essex Lopresti injuries, using predefined clinical and radiological criteria. Interobserver agreement was analyzed using Fleiss Kappa statistics, while intraobserver reliability was evaluated after a two week interval using Cohen Kappa. Overall interobserver agreement was excellent, with a global Fleiss Kappa value of 0.87. Agreement was highest in Galeazzi fractures and lowest in Essex Lopresti injuries, reflecting increased diagnostic complexity in this subgroup. Specialists demonstrated higher agreement than residents. Intraobserver reproducibility was excellent, with identical classifications in 96 percent of reassessed cases. These findings indicate that the proposed classification system shows high reliability and reproducibility, supporting its potential clinical utility for standardized assessment of distal radioulnar joint instability and for guiding future clinical and biomechanical research.