Computed tomographic evaluation of the position of the leg for mortise radiographs.

We investigated the most advantageous internal rotation angle of the leg for mortise radiographs. One hundred and twenty-eight feet of 64 healthy volunteers with no histories of ankle or foot pathology (72 feet of 36 males, 56 feet of 28 females) were examined. The subjects had an average age of 29 years (range, 19 to 51 years), average height of 167 cm (range, 157 to 181 cm), and average foot length of 25 cm (range, 23 to 27 cm). We obtained a plain axial view at the level of the central patella and 5 mm proximal to the tibial plafond using computed tomography, and investigated the inclination angle of the distal tibiofibular joint to a horizontal plane, regarding it as a mortise angle. The mean mortise angle was 19.1 +/- 5.0 degrees. However, two peaks were observed at around 15 degrees and 20 degrees. This indicated that the mean mortise angle of the males was 21.2 +/- 4.6 degrees, and the mean mortise angle of the females was 16.4 +/- 4.1degrees, with a significant difference between the males and the females' mortise angle (P < 0.0001). There was no correlation between the mortise angle and the height (P = 0.899 in the males, and P = 0.871 in the females), nor between the mortise angle and the foot length (P = 0.359 in the males, and P = 0.512 in the females). Therefore, we concluded that the internal rotation angle of the leg for mortise radiography should be generally set up at about 20 degrees on males and 15 degrees on females.