CT measurement of the calcaneal varus angle in the normal and fractured hindfoot.

The calcaneal varus angle is an important parameter used by orthopedic surgeons in their assessment of calcaneal fractures, and restoration of this angle is a major goal in the intraoperative reduction of such fractures. Plain radiographic techniques for the measurement of this angle may be difficult to apply. It is much simpler to measure this angle on CT, which is superior in demonstrating the complex anatomy of the calcaneus. However, a standardized method of measuring this angle by CT has not yet been developed. We measured the calcaneal varus angle in 48 subjects (31 normal feet and 62 feet with fractured calcanei) with three methods. The axial calcaneocuboid angle (the angle in the axial plane between the longitudinal axis of the calcaneus and a line drawn perpendicular to the calcaneocuboid joint) measured 25.3 +/- 7.3 degrees (mean +/- 1 SD) in normal feet and 28.9 +/- 8.5 degrees in fractured feet. The axial talocalcaneal angle (the angle between the longitudinal axes of the talus and the calcaneus in the axial plane) measured 20.9 +/- 9.2 degrees in normal feet and 29.2 +/- 11.3 degrees in fractured feet. The coronal talocalcaneal angle (the angle between the vertical axes of the talus and calcaneus in the coronal plane) measured 12.5 +/- 3.8 degrees in normal feet and 21.8 +/- 7.6 degrees in fractured feet. There was a statistically significant difference between the varus angle for normals and for fractured calcanei by all three methods of measurement (p less than or equal to 0.05). These measurements provide preliminary normative data for three methods of estimating the calcaneal varus angle in the normal and fractured hindfoot. These may be of value not only in the surgical restoration of the normal anatomic alignment of the fractured hindfoot but also in the preoperative assessment of congenital foot abnormalities. Although clinical validation is not yet available, our study suggests that the axial calcaneocuboid angle has several significant advantages over the other two methods.