Boehler's angle: a reappraisal.

Study Objectives: To reappraise Boehler's angle and evaluate factors, including centering of the central beam, sex of subjects, and side of the body, that may affect angle measurement.

Design: Retrospective clinical review.

Setting: Emergency department, Level I trauma center.

Type Of Participants: 120 consecutive patients radiographed for ankle injury who had normal bones on the ankle and/or foot radiographs.

Measurements And Main Results: The mean and SD of Boehler's angle were 30 degrees C +/- 6 degrees (range, 14 degrees to 50 degrees). There was no difference in Boehler's angle between male and female subjects (P greater than .05) or between left and right feet (P greater than .05). Slight variations in central beam location for ankle and foot radiographs had no significant effect on Boehler's angle.

Conclusion: If 28 degrees is taken as the lower limit of normal for Boehler's angle, 37 cases (31%) would be false-positive "abnormal." The use of 20 degrees as the lower limit may decrease the number of false-positive to three cases (2.5%); using 18 degrees (mean -2 SD) reduces the false-positive rate to less than 1% (one case).