Syndesmotic injury, more commonly known as a “high ankle sprain”, accounts for over 12% of all ankle sprain incidents in the US;​ of which, over 25% occur during a sporting activity. Typically, harm to the syndesmosis occurs in sports such as football, soccer, lacrosse, and hockey where it is common for an athlete to experience rapid and extreme dorsiflexion-external rotations of the foot. Severe syndesmotic sprains have been noted by clinicians as the most difficult ankle injury to accurately diagnose and treat, require the most recuperation time, and often results in life-long dysfunction. Even more problematic, 40% of patients suffering from a high ankle sprain also report joint instability 6 months after the initial injury. The distal tibiofibular syndesmosis joint consists of a fibrous interosseous membrane and four stabilizing ligaments, allowing for only slight movements of the fibula about the tibia. These distal bone surfaces closely articulate with the talus to form a stable mortise joint, giving the ankle joint complex its hinge-like range of motion (ROM). In the case of severe ankle sprains, excessive external rotation, dorsiflexion, and eversion of the foot can cause tearing of these stabilizing ligaments, distraction of the bones, or even fracture. A rigid screw fixation method is the standard practice for repair in these severe cases, although new dynamic fixation techniques using sutures and buttons instead of a screw are thought to allow for a more natural motion of the joint during healing and better post-operative results. However, most research of the ankle joint complex has primarily been dedicated to the talocrural joint formed between the talus and tibia, where the fibula is treated as single segment with the tibia. Very little research has been dedicated towards understanding the unique role the fibula plays in dynamic weight-bearing tasks to overall ankle joint strength, stability, and mobility. This gap in knowledge of fibular articulation and load bearing, lends to the difficulty and inaccuracy in properly reducing the bones during syndesmotic fixation. There also lacks a clear and consistent method for syndesmotic fixation with minimal validation that dynamic fixation heeds superior post-operative results. Gaining insight on healthy syndesmosis joint motion could provide baseline measures for more realistic loading conditions of cadaveric testing various fixation devices, serve as design parameters for new device design, set a gold standard for normal range of motion (ROM) in rehabilitation, and ultimately improve diagnostic and treatment modalities for syndesmotic injury.

The goals of the project were to establish a standard for the six degree of freedom (DOF) kinematics in the syndesmosis and talocrural joints in healthy active adults, as well as define the normal ROM. This was done using a high speed stereo radiography (HSSR) system to capture dual plane in-vivo motion of the bones with sub-millimeter and sub-degree accuracy. Changes in bone positioning during static and dynamic weight bearing activities were compared to a non-weight bearing neutral pose of the foot. The second scope of this work defines average values of medial and lateral clear space widening between the bones. Both are current clinical measures used to gauge the degree of ankle injury and instability present. Knowing the kinematics of the bones primarily responsible for stability of the ankle joint complex, along with their expected distraction between each other could help bridge the gap in the diagnosis and treatment of severe high ankle sprains, as well as reduce the risk of incorrect healing and chronic ankle instability.