syndesmosis

A syndesmosis is a fibrous joint in which two adjacent bones are bound together by interosseous ligaments or membranes, forming a syndesmosis. It is one of the fibrous joints, and functionally it is typically immobile or only slightly movable (amphiarthrosis).

The most clinically important example is the distal tibiofibular syndesmosis between the tibia and fibula at the ankle, stabilized by the anterior and posterior tibiofibular ligaments and the interosseous ligament. The interosseous membrane between the radius and ulna in the forearm is another syndesmotic connection that spans the two bones.

The syndesmosis provides stability to the joint by maintaining the relative position of the bones and distributing load across the joint. Injury to a syndesmosis disrupts the ligaments, leading to instability; such injuries are called syndesmotic sprains or high ankle sprains, often resulting from external rotation of the foot or dorsiflexion of the ankle.

Diagnosis is based on clinical examination and imaging, including radiographs, MRI, or CT, with specialized tests to assess tibiofibular alignment and ligament integrity. Treatment ranges from immobilization and rehabilitation for minor injuries to surgical fixation for high-grade injuries, which may involve screws or suture-button devices to restore tibiofibular alignment and stability.