High reliability in classification of tibia fractures in the Swedish Fracture Register

INTRODUCTION: The Swedish Fracture Register (SFR) was started in 2011 and registers fractures of all types, treated either surgically or non-surgically. Twenty-six orthopaedic departments in Sweden are affiliated and a total of 84,000 fractures have been registered. The physician who establishes the diagnosis of the fracture registers and classifies it according to the AO/OTA classification. The accuracy of the classification of fractures is important for the reliability of the data in the SFR. This study aimed to evaluate how accurate the classification of tibia fractures in the register is. METHODS: Three experienced trauma surgeons (raters) were presented with the radiographs of 114 patients with tibia fractures randomly allocated from the SFR. The raters classified the fractures independently and blinded to clinical patient information in two classification sessions with a time interval of one month. The AO/OTA classification coded by the three expert raters (our predefined gold standard) was compared with the classifications in the SFR. Inter- and intra-observer agreement was evaluated. The degree of agreement was reported using the approach of Landis and Koch. RESULTS: The accuracy of the SFR, defined as agreement between the SFR and the gold standard classification, was kappa=0.75 for the AO/OTA type and 0.56 for the AO/OTA group, corresponding to substantial and moderate agreement, respectively. Inter-observer agreement across the three expert raters was kappa=0.74 for the AO/OTA type and 0.53 for the AO/OTA group. Intra-observer agreement was kappa=0.74-0.79 for the AO/OTA type and 0.62-0.64 for the AO/OTA group. CONCLUSION: This study shows that the accuracy of classification of tibia fractures in the SFR was substantial for the AO/OTA type (kappa=0.75) and moderate for the AO/OTA group (kappa=0.56) as defined by Landis and Koch. This degree of accuracy is similar to that in previous studies. We interpret this as meaning that the results of this study demonstrate the high reliability of the data in the SFR and enable the SFR to be used for further scientific analysis.