Computed Tomographic Validation of the Center-Center Radiographic Technique for Syndesmosis Fixation Axis Alignment in Normal Ankles

Background: Ankle syndesmotic ligament injury is an important factor affecting clinical outcome after lower extremity injury with as little as 2 mm of syndesmotic displacement leading to worse clinical outcome. One important factor is the appropriate placement of clamps and fixation across the syndesmosis. When not ideally aligned, these can result in malalignment of the fibula in the incisura. This study sought to provide computer validation of using the center-center technique to identify an ideal centroid axis for placement of syndesmotic implants. Methods: Thirty computed tomography (CT) scans of patients from July 1, 2016, to June 30, 2018, with normal syndesmoses were evaluated. Center-center and centroid measurements were drawn and compared on the axial CT images at 10, 20, and 30 mm superior to the tibial plafond. Three observers recorded measurements for the same 50 patients in order to compare interobserver reliability. Results: The difference between the centroid and center-center axis at each height level was a mean 0.4 degrees (range, 0.3-0.5 degrees). The center-center and centroid axis change by externally rotating as the height increases away from the tibial plafond with mean, 3 degrees (range, 0-6.1 degrees). Intraclass correlation coefficients (ICCs) were measured at 0.98, thus demonstrating excellent intraobserver and interobserver reliability on these measurements. Conclusion: The center-center technique can be used to identify the centroid axis within an acceptable degree of rotation at heights above the tibial plafond that are relevant to an operating surgeon placing syndesmotic fixation. Clinical Relevance: Theoretically, this aligns the centroids of the fibula and tibia, which achieves the same ideal patient-specific alignment and raises the question as to the extent to which the centroid and center-center axes correlate in the general population. If present, a strong correlation has potentially high clinical importance when planning syndesmotic fixation.