Radiographic identification of the primary structures of the ankle syndesmosis.

Purpose: The purpose of this study was to quantitatively describe the locations of the syndesmotic ligaments and the tibiofibular articulating cartilage surfaces on standard radiographic views using reproducible radiographic landmarks and reference axes.

Methods: Twelve non-paired ankles were dissected to identify the anterior-inferior tibiofibular ligament (AITFL), posterior-inferior tibiofibular ligament (PITFL), interosseous tibiofibular ligament (ITFL), and the cartilage surfaces of the syndesmosis. Structures were marked with 2-mm radiopaque spheres prior to obtaining lateral and mortise radiographs. Measurements were performed by two independent raters to assess intra- and interobserver reliability via intraclass correlation coefficients (ICCs).

Results: Measurements demonstrated excellent agreement between observers and across trials (all ICCs ≥ 0.960). On the lateral view, the AITFL tibial origin was 9.6 ± 1.5 mm superior and posterior to the anterior tibial plafond. Its fibular insertion was 4.4 ± 1.7 mm superior and posterior to the anterior fibular tubercle. The centre of the tibial cartilage facet of the tibiofibular contact zone was 8.4 ± 2.1 mm posterior and superior to the anterior plafond. The proximal and distal aspects of the ITFL tibial attachment were 45.9 ± 7.9 and 12.4 ± 3.4 mm proximal to the central plafond, respectively. The superficial and deep PITFL coursed anterior and distally from the posterior tibia to fibula. On the mortise view, the AITFL tibial attachment centre was 5.6 ± 2.4 mm lateral and superior to the lateral extent of the plafond (4.3 mm lateral, 3.3 mm superior), and its fibular insertion was 21.2 ± 2.1 mm superior and medial to the inferior tip of the lateral malleolus.

Conclusions: Quantitative radiographic guidelines describing the locations of the primary syndesmotic structures demonstrated excellent reliability and reproducibility. Defined guidelines provide additional clinically relevant information regarding the radiographic anatomy of the syndesmosis and may assist with preoperative planning, augment intraoperative navigation, and provide additional means for objective postoperative assessment.