A syndesmosis is a type of articulation, or joint, in which two adjacent bones are joined by an interosseous membrane. Along with symphysis joints, syndesmoses are classified as amphiarthrosis joints in that they allow slight movement. Joints of this kind are found at several points in the human body, including the intermediate radioulnar joint, where the radius and ulna meet above the wrist; in the spine between the spinous processes of various adjacent vertebra; and above the ankle joint where the tibia and fibula converge.
To illustrate the structure of a syndesmosis joint, the ankle articulation is a prime example. Located directly above the ankle joint, a synovial hinge joint, the ankle syndesmosis is held together by four ligaments. The anterior inferior tibiofibular ligament (AITFL) crosses in front of the tibia and fibula bones; the posterior inferior tibiofibular ligament (PITFL) and the transverse ligament connect the two bones from behind; and the interosseous ligament runs between the contiguous bony surfaces of the two bones.
Due to the lack of flexibility in these joint structures, ligament injuries in these joints are not uncommon, particularly at the wrist and ankle. When the wrist or ankle joint is bent beyond its normal range of motion, a sprain or even a tear in these ligaments can occur. Mild syndesmosis injury may involve the sprain of a single ligament; more severe injuries can involve damage to multiple ligaments at once, or even the separating of the bones at the joint — known as diastasis.
Ankle syndesmosis injury is perhaps the most common and is referred to as a high ankle sprain, as the injury occurs just above, or superior to, the ankle joint. Orthopedists report a frequency of such injuries in athletes, such as football players and snow skiers, where the foot is bent outward at the ankle joint — these injuries are often misdiagnosed as an ankle sprain. The result of such an injury is a joint that is unstable and in some cases may require surgery to repair the ligament damage. Additionally, injuries can be more painful and take longer to heal than regular sprains, and high-impact activities, such as jogging and jumping, should generally be avoided until advised otherwise by a physician.