Templating of Syndesmotic Ankle Lesions by Use of 3D Analysis in Weightbearing and Classical CT

Abstract

Category: Ankle Introduction/Purpose: Syndesmotic lesions of the ankle have shown to be challenging injuries towards diagnosis and surgical treatment. This could be mainly attributed to the limitations of 2D imaging, which make it difficult to accurately determine the extent of the lesion and to verify if peroperatively an anatomical reduction is achieved of the distal tibiofibular congruence. The aim of this study is therefore to develop a reproducible method to quantify the displacement in a syndesmotic ankle lesion in all six degrees of freedom based on 3D imaging. Methods: Eighteen patients were retrospectively included having a unilateral syndesmotic lesion. N=12 sustained a high ankle sprain and a bilateral weightbearing conebeam CT was obtained because of positive clinical syndesmotic tests. N=6 presented with a fracture associated syndesmotic lesion and were imaged by a bilateral non-weightbearing CT. The non-affected ankle was used as a template after being mirrored and matched on the contralateral ankle containing a syndesmotic lesion (Fig 1A-B). The distal fibula was marked by computer calculation of the most outer point of the anterior tubercle, posterior tubercle and apex malleolis lateralis. The change of these points towards the unaffected fibular position was used to quantify the syndesmotic lesion (Fig 1C). A control group of seven patients (N=7) was used to analyse if these changes differed from the normal variation in tibio-fibular congruency (Fig 1D). Results: The main findings consisted of a statistical significant difference in the mean mediolateral diastasis of both the sprained group (M = 1.60 mm, SD=1.02) and the fracture group (M = 1.69 mm, SD=0.62) compared to the control group (P<.001). The mean external rotation was statistically different when comparing the sprained group (M = 4.68°, SD=2.74) and the fracture group (M = 6.97°, SD=3.02) towards the control group (P<.05). The mean antero-posterior translation was only significantly different when comparing the fracture group (M = -4.73 mm, SD=4.53) towards the sprained group (M = -0.91 mm, SD=1.26) and the control group (M = -0.26 mm, SD=1.53) (P<.05). Conclusion: This study demonstrates an effective method to quantify a unilateral syndesmotic lesion of the ankle. The pathological measurements differed from the normal distal tibio-fibular configuration in the syndesmotic complex. This sequential analysis is of use for an accurate diagnosis and a pre-operative planning to know in advance which correction needs to be achieved to have the fibula at proper length correctly rotated, and reduced into the syndesmosis with no anterior, posterior or lateral displacement.