Normal Kinematics of the Syndesmosis and Ankle Mortise During Dynamic Movements

BACKGROUND: Documenting the healthy articulation of the syndesmosis and talocrural joints, and measurement of 3D medial and lateral clear spaces may improve diagnostic and treatment guidelines for patients suffering from severe syndesmotic injury or chronic instability. This study aimed to define the range of motion (ROM) and displacement of the fibula and talus during static and dynamic activities, and measure the 3D movement in the tibiofibular (syndesmosis) and medial clear space. METHODS: Six healthy volunteers performed dynamic weightbearing motions on a single-leg: heel-rise, squat, torso twist, and box jump. Participants posed in a nonweightbearing neutral stance as well as weightbearing neutral standing, plantarflexion, and dorsiflexion. High-speed stereoradiography measured 3D rotation and translation of the fibula and talus throughout each task. Medial clear space and tibiofibular gap distances were measured under each condition. RESULTS: Total ROM for the fibula was greatest in internal-external rotation (9.3 ± 3.5 degrees), and anteroposterior (3.3 ± 2.2 mm) and superior-inferior (2.5 ± 0.9 mm) translation, rather than lateral widening (1.7 ± 1.0 mm). The total rotational ROM of the talus was greatest in dorsiflexion-plantarflexion (34.7 ± 12.9 degrees) and internal-external rotation (15.0 ± 3.4 degrees). Single-leg squatting increased the lateral clear space (P = .045) and widened the medial tibiofibular joint, whereas single-leg heel-rises decreased the lateral clear space (P = .001) and widened the tibiotalar space. Gap spaces in the tibiofibular and medial clear spaces did not exceed 2.3 ± 0.9 mm and 2.7 ± 1.2 mm, respectively. CONCLUSION: These data support a potential shift in the clinical understanding of fibula displacements during dynamic activities and how implant device constructs might be developed to restore physiologic mechanics. CLINICAL RELEVANCE: Syndesmosis stabilization and rehabilitation should consider restoration of normal physiologic rotation and translation of the fibula and ankle mortise rather than focusing solely on the restriction of lateral translation.