How Does Mechanism of Injury Relate to Similar Fracture Patterns in Bilateral Displaced Intra-articular Calcaneal Fractures?

Several biomechanical/cadaver studies have established a correlation between mechanism of injury and fracture classification in calcaneal fractures. However, this has never been backed up by clinical studies. In this study, the hypothesis is tested whether the alleged similar mechanism of injury for both feet in bilateral calcaneal fractures leads to similar fracture types. In this retrospective cross-sectional cohort study, patients with unilateral and bilateral calcaneal fractures treated between 2000 and 2017 were classified according to Essex-Lopresti and Sanders. Positive predictive values were computed, signifying the chance that the fracture type in the left foot corresponded to that in the right foot. These were compared to the a priori chance of a fracture type (percentage of fracture type in unilateral fractures) by constructing 95% confidence intervals of the positive predictive value of each fracture type. Of the 451 patients, 413 (91.6%) had unilateral and 38 (8.4%) bilateral calcaneal fractures. Mechanisms of injury were similar for uni- and bilateral fractures. Using the Essex-Lopresti fracture classification, 34 cases (90%) had the same classification in both feet, compared with 24 (63%) in the Sanders classification. The chance of a fracture type in the left, with the right foot as reference, was significantly larger than expected from a priori chance in the unilateral population. This leads to a new hypothesis, that, more than mechanism of injury, the magnitude of the impact and the position of the foot are important in predicting fracture classification in the calcaneus.