Coronal shear fractures of the capitellum and trochlea: interobserver variability in classifying the fracture and the need for a computed tomography scan for the correct surgical planning

BACKGROUND: To determine interobserver agreement in the classification by X-rays and by computed tomography (CT) scan of the coronal shear fractures of the capitellum and trochlea as well as the agreement between these two tests. METHODS: Patients with coronal shear fractures of the capitellum who were managed at our center between January 2008 and December 2017 were included. This retrospective cohort study was carried out with the approval of the ethics committee of our institution (Nº: IIBSP-Cod-2019-02, Ref. 19/070). Clinical, radiographic, and elbow-specific outcomes, including the Mayo Elbow Performance Index, were evaluated. Three observers analyzed the preoperative X-rays from all the cases. Each one of them independently classified the fractures according to the Bryan and Morrey classification (with the modification of McKee et al). The interobserver agreement was calculated by Cohen kappa coefficient. The same methodology was used to analyze the CT scan. Thereafter, one single value was determined for each X-ray and CT scan, from the good interobserver agreements. Finally, the agreement between the global X-ray classification and the global CT scan classification was calculated using the agreement percentage and the Cohen kappa coefficient. RESULTS: There were 3 males and 6 females, with a mean age of 47 years (range, 18-83). The mean follow-up period was 18 months (12-40). The average Mayo Elbow Performance Index score was 85 (range, 65-100) points. The complications were nonunion in one patient (11 %), degenerative arthritis in 7 (78 %), joint step-off in 5 (55%), and heterotopic ossification in 7 (78%). The agreement analysis between the global X-ray classification and the global CT scan classification showed a 57.1% agreement, with a kappa coefficient of −0.167. These values imply the absence of agreement. CONCLUSION: Our results demostrated that simple X-rays do not allow for the adequate interpretation of distal humeral coronal plane fractures. Although an acceptable interobserver agreement was found, there is no agreement when the same fractures were analyzed by CT scan. The authors routinely recommend CT scan to assess the extent of the fracture and perform surgical planning.