Correlation and comparison of syndesmosis dimension on CT and MRI

F. Wong, N. Mushtaq, I.T. Jones, S. Singh, A. Abbasian, R.Mills

Introduction: Recent published studies have examined the normal dimensions of the syndesmosis on CT. However, previous anatomical studies have shown variations of the articulating facets within the tibialae fibularis and may contribute to the false appearance of increased spacing within the syndesmosis. In this study, we measured and compared anterior and posterior distances of the distal tibiofibular (DTF) syndesmosis on MRI and CT imaging.

Methods: We identified adult patients who had had both a CT scan and an MRI scan of their ipsilateral ankle to investigate symptoms unrelated to the DTF syndesmosis. The anterior and the posterior DTF dimensions were measured on CT and MRI axial images, at the level of the distal tibial physeal scar. This was taken from anterior tubercle of tibia and from the most anterior aspect of the posterior tibial tubercle to the nearest point of medial aspect of the fibula. The geometrical shapes of the syndesmosis and the anterior tibial tubercle were also recorded.

Results: 16 ankles in 15 patients were included. The mean age was 34.6+/-8.8 years. The mean (SD) for the anterior DTF distance was 2.0mm (0.7mm) on MRI and 2.9mm (0.9mm) on CT whilst the mean posterior DTF distance was 3.2mm (1.1mm) on MRI and 4.3mm (1.0mm) on CT. This difference reached statistical significance (p < 0.001, paired T-test). When examining the shape of the syndesmosis on MRI, 56% were crescent and 44% rectangular, this was compared to 69% and 31%, respectively, on CT. There was, however, no statistical difference in the shape of the syndesmosis between the two radiological modalities (p = 0.625, McNemar test).

Conclusion: CT appears to over-estimate the distal tibiofibular separation and may lead to a false positive diagnosis. Further studies are needed to establish the reliability in the use of CT scans to investigate normal and abnormal syndesmosis.