The effects of rotation on radiographic evaluation of the tibiofibular syndesmosis.

Radiographs of 12 normal cadaveric lower extremities were prepared with each extremity in seven increments of axial rotation, ranging from 5 degrees of external rotation to 25 degrees of internal rotation. The tibiofibular clear space, the tibiofibular overlap, the width of the tibia and fibula, and the medial clear space were measured on each film. The width of the tibiofibular clear space (syndesmosis A) averaged 3.9+/-0.9 mm (range, 2 to 5.5 mm), but did not change significantly with rotation. Its size was independent of the size of tibia and fibula. All other measurements changed dramatically with rotation. In our specimens, a true mortise view of the ankle joint was obtained by internally rotating the extremity an average of 13.6+/-0.7 degrees (range, 12.0 degrees to 17.0 degrees). Based on our results the width of the tibiofibular clear space on the anterior-posterior view is the most reliable parameter for detecting widening of the syndesmosis on plain radiographs. However, due to its variability among different individuals, comparison views of the contralateral extremity are warranted for confirmation of clinical suspicion of syndesmosis disruption.