Reliability of the CURL classification for proximal ulna fracture-dislocations of the elbow

Abstract

BackgroundProximal ulna fracture-dislocations are challenging injuries with a myriad of existing classification systems. The Coronoid, proximal Ulna, Radius and Ligaments (CURL) classification is a simple framework designed to focus attention on the key components affecting outcome and guide surgical management. This study evaluates inter- and intra-observer reliability of this new classification. MethodsFour observers independently reviewed plain radiographs and CT scans of patients with proximal ulna fracture-dislocations. Each observer scored the Coronoid (C), proximal Ulna (U) and Radius (R) components for each fracture on two occasions. The osseous components were sub-classified as ‘intact’, ‘simple’ or ‘complex’. The Ligament component (L) was not rated as this requires intra-operative classification. Inter- and intra-observer reliability was calculated using Cohen’s weighted kappa coefficients. X-ray and CT were compared for patients with both imaging modalities. The Landis and Koch criteria were used to interpret the strength of the kappa statistics. Results177 patients had plain X rays, 58 patients had both X ray and CT scans. Overall, in the X ray only cohort, there was ‘almost perfect’ inter-observer reliability for the radial head (k=0.94) and coronoid (k=0.83), and ‘substantial’ reliability (k=0.68) for the proximal ulna. For the X ray and CT cohort, inter-observer reliability was ‘almost perfect’ across both modalities for the radial head (k=0.88 and k=0.93, respectively) and ‘moderate’ for the proximal ulna (k=0.48 and k=0.52, respectively). For the coronoid, inter-observer reliability for X-ray interpretation was ‘substantial’ (k=0.74) and for CT was ‘almost perfect’ (k=0.89). Intra-observer reliability was ‘almost perfect’ for all components, other than CT assessment of the proximal ulna which demonstrated ‘substantial’ reliability (k=0.74). ConclusionThe CURL classification demonstrates strong inter- and intra-observer reliability, supporting use of the classification for proximal ulna fracture-dislocations. CT is recommended for improved characterization of any fracture with a coronoid component.