Radiographic Identification of the Syndesmotic Structures of the Ankle

OBJECTIVES: Syndesmotic ligament sprains may result in significant time lost from sport and can lead to chronic pain and instability. While syndesmotic anatomy has been well-defined, quantitative radiographic guidelines for identifying the anatomic ligament attachment sites and tibiofibular cartilage surfaces have not been adequately defined. The purpose was to define quantitative radiographic guidelines for identifying the origins and insertions of the syndesmotic ligaments and tibiofibular articulating cartilage surfaces with respect to radiographic landmarks and standard reference lines. METHODS: Twelve non-paired fresh-frozen ankles were dissected to identify the attachments of the anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), interosseous tibiofibular ligament (ITFL), and the cartilage surfaces of the tibiofibular articulation. The center of each structure was marked with a 2 mm radiopaque sphere at the level of the cortex. Standard lateral and mortise radiographs were obtained using a fluoroscopy c-arm and calibrated using a 25.4 mm diameter radiopaque sphere positioned in the field of view. Using a picture archiving and communications system, measurements were performed twice by two independent raters to calculate intra- and inter-rater reliability via intraclass correlation coefficients (ICCs). RESULTS: Measurements demonstrated excellent agreement between raters and across trials (All inter- and intra-rater ICCs ≥ 0.960) for all structures and radiographic views. On the lateral view, the AITFL tibial origin was 9.6 ± 1.5 mm superior and posterior to the anterior tibial plafond (Table 1). Its fibular insertion was 4.4 ± 1.7 mm superior and posterior to the anterior fibular tubercle. The superficial PITFL originated 7.4 ± 1.6 mm superior to the posterior plafond and inserted 22.0 ± 2.3 mm superior and posterior to the lateral malleolus. The corresponding measurements for the deep PITFL were 3.2 ± 1.5 mm superior and 15.4 ± 3.4 mm superior and posterior, respectively. The proximal and distal edges of the ITFL tibial origin were 45.9 ± 7.9 mm and 12.4 ± 3.4 mm proximal to the central aspect of the plafond respectively. The center of the tibiofibular contact area was 8.4 ± 2.1 mm posterior and superior to the anterior plafond. On the mortise view, the AITFL tibial attachment was 5.6 ± 2.4 mm medial and superior to the lateral extent of the plafond and its fibular insertion was 21.2 ± 2.2 mm superior and medial to the lateral malleolus. The corresponding superficial PITFL measurements were 2.7 ± 1.7 mm and 21.5 ± 3.2 mm respectively. The ITFL distal tibial margin was 11.1 ± 3.5 mm proximal to the tibial plafond. CONCLUSION: Radiographic measurements demonstrated excellent agreement among reviewers and across trials suggesting clinical reproducibility and surgical utility of the defined parameters. Regardless of the type of surgical treatment, these parameters will assist with preoperative planning, augment intraoperative navigation, and provide additional means for objective post-operative assessment of hardware and tunnel placement. Furthermore, radiographic landmarks may be of particular use in revision or arthroscopic assisted cases where surgical landmarks may be obscured or not readily visible.