Abstract
Syndesmotic ankle injuries are present in one fourth of all ankle trauma and may lead to chronic syndesmotic instability as well as posttraumatic ankle osteoarthritis. The main challenge remains distinguishing them from other types of ankle trauma. Currently, the patient's injured and non-injured ankles are compared using plain radiographs to determine pathology. However, these try to quantify 3D displacement using 2D measurements techniques and it is unknown to what extent the 3D configuration of the normal ankle syndesmosis is symmetrical.
We aimed to assess the 3D symmetry of the normal ankle syndesmosis between the right and left side in a non- and weightbearing CT.
In this retrospective comparative cohort study, patients with a bilateral non-weightbearing CT (NWBCT; N=28; Mean age=44, SD=17.4) and weight-bearing CT (WBCT; N=33; Mean age=48 years; SD=16.3) were analyzed. Consecutive patients were included between January 2016 and December 2018 when having a bilateral non-weightbearing or weightbearing CT of the foot and ankle. Exclusion criteria were the presence of hindfoot pathology and age less than 18 years or greather than 75 years. CT images were segmented to obtain 3D models. Computer Aided Design (CAD) operations were used to fit the left ankle on top of the right ankle. The outermost point of the apex of the lateral malleolus (AML), anterior tubercle (ATF) and posterior tubercle (PTF) were computed. The difference in the coordinates attached to these anatomical landmarks of the left distal fibula in the ankle syndesmosis with respect to right were used to quantify symmetry. A Cartesian coordinate system was defined based on the tibia to obtain the direction of differences in all six degrees of freedom. Statistical analysis was performed using the Mann-Whitney U test to allow comparison between measurements from a NWBCT and WBCT. Reference values were determined for each 3D measurement in a NWBCT and WBCT based on their 2SD. The highest difference in translation could be detected in the anterior-posterior direction (Mean APNWBCT= −0.01mm; 2SD=3.43/Mean APWBCT=−0.1mm; 2SD=2.3) and amongst rotations in the external direction (Mean APNWBCT=−0.3°; 2SD=6.7/Mean APWBCT=-0,2°; 2SD=5.2). None of these differences were statistically significant in the normal ankle syndesmosis when obtained from a NWBCT compared to a WBCT (P>0.05).
This study provides references values concerning the 3D symmetry of the normal ankle syndesmosis in weightbearing and non-weightbearing CT-scans. These novel data contribute relevantly to previous 2D radiographic quantifications. In clinical practice they will aid in distinguishing if a patient with a syndesmotic ankle lesion differs from normal variance in syndesmotic ankle symmetry.
