Morphology of the Incisura Fibularis at the Distal Tibiofibular Syndesmosis in the Japanese Population

The morphology of the distal tibiofibular syndesmosis can determine the pathology and mechanism of syndesmotic injury. The present study assessed measurements obtained from computed tomography (CT) images of the normal distal tibiofibular syndesmosis in Japanese subjects. CT scans of 120 right feet with a normal distal tibiofibular syndesmosis obtained from January 2009 to December 2016 were retrospectively assessed at the level 10 mm proximal to the tibial plafond. The incisura fibularis was considered concave when its depth was ≥4 mm and shallow when its depth was <4 mm. The depth of the incisura fibularis, anterior tibiofibular distance (TFD), posterior TFD, and longitudinal/transverse length of the distal fibula were measured. The incisura fibularis was concave in 64.2% of the feet and shallow in 35.8%. The mean anterior TFD was 2.2 ± 0.8 mm (2.4 ± 0.8 mm in males; 2.1 ± 0.8 mm in females; 2.1 ± 0.8 mm for concave; 2.2 ± 0.9 mm for shallow). The mean posterior TFD was 5.9 ± 1.6 mm (6.7 ± 2.1 in males; 5.7 ± 1.3 mm in females; 5.5 ± 1.3 mm for concave; 6.5 ± 1.9 mm for shallow). The mean longitudinal/transverse length of the distal fibula at the level of the syndesmosis was 1.2 mm (1.3 mm in males; 1.2 mm in females; 1.1 mm for concave; 1.3 mm for shallow). The mean posterior TFD was significantly greater than the mean anterior TFD and was also significantly greater in males than in females. Significant differences were found in the body mass index, posterior TFD, and longitudinal/transverse length of the distal fibula according to whether the incisura fibularis was concave or shallow. The present study has provided measurements of the normal tibiofibular syndesmosis in the Japanese population. These data suggest that the morphology of the syndesmosis varies, especially with respect to whether the incisura fibularis is concave or shallow.