Effect of tube angulation on the measurement of intermetatarsal angles.

We systematically investigated the effect of tube angulation on angular distortion of the anteroposterior radiograph of the foot. Three-dimensional data from the metatarsals originating from computed tomographic scans of ten healthy volunteers were projected onto the supporting surface at various tube angulations to simulate radiography. The distortion of the intermetatarsal angles decreased from 1.2 degrees to 3.5 degrees at 20 degrees tube angulation to 0.4 degrees to 2.7 degrees at 0 degrees tube angulation. The relatively small improvement in angular measurement using 0 degrees instead of 15 degrees tube angulation would not outweigh the adverse effects of changing the standard radiographic technique. Physician awareness of this source of error when planning surgical therapy seems more important.