Radiological assessment of ankle syndesmotic reduction

The intraoperative assessment of adequacy of syndesmotic reduction is challenging. The aim of this study was to develop a radiographic measure based on the lateral ankle view to assess both the normal and abnormal relationship between the tibia and fibula after simulated syndesmotic malreduction and to evaluate the effect on commonly used mortise measurements.

Mortise and talar dome lateral radiographs were obtained in eight fresh-frozen cadaveric specimens before and following syndesmosis division and posterior fibular displacement of 2mm increments. Using the technique described, on the lateral radiograph the anterior fibular line ratio (AFL ratio) and posterior fibular line distance (PFL distance) were measured. Both measures were based on the anterior and posterior distal tibia articular margins and flat borders of the fibula.

Inter- and intraobserver reliability of the AFL ratio and PFL distance measured almost perfect agreement. In all uninjured specimens the AFL lay just anterior to the midpoint of the tibia and the PFL intersected the posterior tibia articular margin or lay just anterior to it, not posterior. At 2, 4 and 6mm of posterior fibular displacement the decrease in AFL ratio and PFL distance showed significant differences between all pairwise comparisons.

The proposed new measures of syndesmotic reduction are reproducible and capable of detecting from 2mm of sagittal fibula displacement and can be useful adjuncts in the assessment of syndesmotic reduction.