CT characterizing the anatomy of uninjured ankle syndesmosis

Although it is expert opinion that transsyndesmotic screws are placed obliquely 30° from posterolateral to anteromedial in the transverse plane, this has not been formally studied, and there is inconsistency regarding the congruency of the distal tibiofibular joint. Thirty-eight computed tomography (CT) scans of the lower extremity were used to examine the rotational profile of the axis of the syndesmotic joint in relation to the femoral transepicondylar axis and to describe the congruency of this joint. The axis of the distal tibiofibular joint was 32°±6° externally rotated in relation to the transepicondylar axis. The average anterior, central, and posterior widths of the syndesmotic joint space 10 mm superior to the joint line were statistically significantly different: 1.7±0.9 mm, 1.7±0.6 mm, and 2.3±1.1 mm, respectively (P=.004). This study demonstrates that the axis of the uninjured distal tibiofibular joint is approximately 30° externally rotated in relation to the transepicondylar axis. Therefore, reduction clamps and screws should be placed at this angle to avoid malreduction of the syndesmosis. The posterior joint space width is significantly wider than the anterior and central joint spaces. This study's results provide a description of the anatomy of the uninjured distal tibiofibular joint to guide reduction maneuvers and establish a baseline for evaluation of postreduction CT scans.