Good morning, everybody. Thanks for being present for this talk. My name is Taylor Dunhartog. I'm one of the third-year residents at the University of Iowa. I'll be presenting this topic, defining normal values for tibiofibular syndesmotic space with and without external rotation stress. So diagnosis and treatment of distal tibiofibular syndesmosis, or DTFS, injury and instability can be a very challenging topic. We need to remember that syndesmotic instability is not necessarily the same entity as acute syndesmotic injury, and this project focused more on subtle syndesmotic instability. And conventional two-dimensional radiographs can be difficult to interpret when assessing for subtle instability. MRI is very sensitive but may miss dynamic instability unless bony relationships have become abnormal statically. Conventional CT assesses bony structure only in a non-stressed state. And arthroscopy is the gold standard because it permits direct visualization but is invasive, costly, and requires anesthesia. This paper by Hagemeyer looked at 12 patients with unilateral syndesmotic instability. They found a statistically significant difference in the syndesmotic area between the injured and uninjured ankles, but had a fairly wide range of confidence intervals. And then this paper is a follow-up by Dr. Esfahani. It's a retrospective view looking at 24 patients with subtle syndesmotic instability in the acute or subacute period that were confirmed with arthroscopy. When assessing for the area, they found that the area one centimeter above the tibial plafond had a 75% accuracy in predicting syndesmotic instability. Our aim was to evaluate the differences in DTFS area in both natural weight-bearing position as well as external rotation stress. We also wanted to report normal threshold values for DTFS area measurements and healthy volunteer controls. So the question is, does external rotation stress matter? This paper by Krah and Bull was a cadaveric progressive sectioning of ligaments. They found that axial weight-bearing load and isolation had no impact on their measurements, but when external rotation was added, it led to significant syndesmotic widening. We took 24 healthy volunteers without any history of DTFS injury, high ankle sprain, previous foot and ankle surgery, or current ankle pain. They underwent bilateral non-stress and external rotation stress weight-bearing CT scans. Our various external rotation stress views were obtained by having the patient maximally internally rotate the leg while the foot was held in a fixed planted rig position. The DTFS area was semi-automatically quantified on axial plane weight-bearing CT images using dedicated software. The apex of the distal tibia articular dome was digitally imaged using the software program and a second mark was made approximately one centimeter proximal to that. The area of the syndesmosis was then delineated by two tangential lines from the anterior and posterior cortices of the tibia. The area between the fibula and the distal tibia between the two marked lines were then calculated in millimeters squared based on Hounsfield Unit's algorithm. Syndesmosis area values were compared between non-stressed and stressed ankles as well as left versus right. Overall we found no statistically significant difference between stressed and non-stressed ankles in these healthy controls as well as no difference in laterality. So in conclusion, diagnosis of DTFS instability with two-dimensional imaging can be very challenging and weight-bearing CT has emerged as a useful tool for subtle instability. Weight-bearing CT with external rotation stress did not result in any significant widening of DTFS in healthy volunteers and baseline values in healthy ankles with external rotation stress were observed to be 103.8 millimeters squared. We hope to be able to use these baseline values going forward as a baseline for other projects. Thank you.

Taylor Dunhartog

University of Iowa

distal tibiofibular syndesmosis

diagnosis and treatment

syndesmotic instability