Canterbury index : an accurate predictor of fracture re-displacement?

Abstract

PURPOSE: Paediatric forearm fractures are commonly seen and treated by closed reduction and plaster cast application in theatre. Historically cast application has been subjectively evaluated for its adequacy in maintaining fracture reduction. More recently emphasis has been placed on objectively evaluating the adequacy of cast application using indicators such as the Canterbury index (CI). The CI has been used in predicting post-reduction, re-displacement risk of patients by expressing the cast and padding indexes as a ratio. The CI has been criticised for not including cast three-point pressure, fracture personality, lack of standardisation of X-ray views as well as practical requirement of physical measurement using rulers. The aim of this study was to determine whether subjective evaluation of these indices, before and after a tutorial on the CI, was accurate in predicting a patient’s ultimate risk of re-displacement, following reduction and casting. In addition, we aimed to determine whether objective evaluation of these indices by measurement on the hospital’s digital X-ray system correlated with the final fracture outcome post-reduction. MATERIALS AND METHODS: A retrospective study was done on a sample of 11 patients during the period May 2010 to July 2011 at Steve Biko Academic Hospital. In total, 44 X-rays/fluoroscopy views were subjectively evaluated by 20 registrars and eight consultants for possible fracture re-displacement, before and after a tutorial on the CI. Five consultants and 10 registrars each measured 22 cast, padding and CIs on the digital X-ray system. RESULTS: A formal tutorial did not produce an increase in subjective predictive accuracy. Pre- and post-tutorial observed agreement was seldom better than agreement by chance alone. Poor strength of agreement (κ <0.20) was found in all groups, irrespective of level of displacement, imaging modality, level of orthopaedic training and tutorial attendance. Objective measurement of the indexes all had insignificant p-values for comparing groups, indicating that there was no correlation between the measured indexes and the final outcome irrespective of the level of fracture, imaging modality and level of orthopaedic training. Shortcomings were variable co-operation from participants and non-standardisation of X-rays. CONCLUSION: In our hospital setting, no clinical value for the subjective and/or objective use of the CI could be found. Subjective agreement was almost the same as expected agreement and objective measurement indicated no correlation with the fracture outcome. It is suggested that patients following closed reduction of forearm fractures be followed up within the first three days, and regularly thereafter, as there is currently no ideal system to predict re-displacement. Further studies are needed to validate the CI by standardisation of X-rays.