FA5: THE DIAGNOSTIC ACCURACY OF BÖHLER’S ANGLE IN FRACTURES OF THE CALCANEUS

Abstract

Böhler’s historical tuber-joint angle of the calcaneus has been used since 1931. Surprisingly, there is a paucity of literature on the topic. The aims of this study were to confirm the normal range for Böhler’s angle and determine the angle with the highest accuracy in the diagnosis of calcaneal fractures.

A retrospective cohort study was performed. Data were obtained from The St George Hospital digital Picture Archival and Communication System (PACS) and through a review of medical records. The study cohort comprised 212 consecutive patients diagnosed with calcaneal fractures on CT scan, spanning a five-year period from April 2003 to March 2008. An additional 212 patients with normal lateral foot radiographs were used to determine the normal range. Böhler’s angle was measured by two independent observers on lateral xray using the digital angle tool from PACS. Data were analysed using Stata 8 statistical software package.

This is the largest study to our knowledge that examines the diagnostic accuracy of Böhler’s angle in fractures of the calcaneus. Contrary to many texts but true to Böhler’s assertions, the mean Böhler’s angle in patients without calcaneal fracture was 29.4 degrees (95% CI, 28.9–30.0 degrees). In this group there was no difference in Böhler’s angle between male and female patients (p> .05), left and right feet (p> .05) or across age (ANOVA, p> .05). In those patients with calcaneal fractures, a Böhler’s angle below 25 degrees was moderately predictive of calcaneal fracture (sensitivity = 100%, specificity = 82%, PPV = 85%, NPV = 100%, LR+ = 5), an angle below 23 degrees was highly predictive of calcaneal fracture (sensitivity = 100%, specificity = 89%, PPV = 90%, NPV = 100%, LR+ = 9) and an angle below 21 degrees was strongly suggestive of calcaneal fracture (sensitivity = 99%, specificity = 99%, PPV = 99%, NPV = 99%, LR+ = 110). A Böhler’s angle of less than or equal to 20 degrees had the highest diagnostic accuracy as there were only two false negatives and one false positive from a total of 424 patients.

A Böhler’s angle of 20 degrees or less is highly accurate in determining the presence or absence of calcaneal fracture. These findings are of particular importance when fracture is uncertain as it gives the surgeon a definitive reference point when using Böhler’s angle for assessment of fracture of the calcaneus.