A syndesmosis is a fibrous joint where two bones connect directly by fibrous connective tissue. Unlike other joints, its uniting material does not allow extensive movement, primarily serving stabilization.
The Connecting Tissues
The fibrous connective tissue uniting bones comes in two forms: ligaments or an interosseous membrane. Ligaments are dense, strong bands of fibrous tissue that provide tensile strength, binding bones and limiting their separation.
An interosseous membrane is a broad, flat sheet of fibrous connective tissue. It spans between two bones, forming a wide connection. Both ligaments and interosseous membranes contribute to the structural integrity and limited mobility of syndesmosis joints.
Common Locations in the Body
Syndesmosis joints are found in several locations, where their structure supports specific functions. An example is the joint between the tibia and fibula in the lower leg, where an interosseous membrane unites these two long bones.
In the forearm, an interosseous membrane connects the radius and ulna. These sheets hold the bones together and provide surfaces for muscle attachment. They also allow some rotational movement while maintaining structural cohesion.
Specific Ligaments of the Ankle
The distal tibiofibular syndesmosis, located just above the ankle joint, is an example of a syndesmosis held by multiple ligaments. This joint connects the distal ends of the tibia and fibula, and is important for ankle stability.
Several ligaments contribute to this syndesmosis. The anterior inferior tibiofibular ligament (AITFL) crosses from the tibia to the fibula on the front. The posterior inferior tibiofibular ligament (PITFL) provides stability on the posterior side, spanning between the tibia and fibula.
Deep within the joint, the interosseous ligament is a strong, fibrous connection, continuing the interosseous membrane down to the ankle. Further enhancing posterior stability, the transverse tibiofibular ligament is a deep band of the PITFL that connects the malleoli.
Role in Body Movement and Stability
Syndesmosis joints balance limited movement and stability. Unlike mobile synovial joints, their fibrous connections restrict the range of motion between articulating bones. This limited movement is often a slight yielding or rotation, rather than extensive flexion or extension.
Their primary function is to provide structural support and prevent bone separation. For instance, interosseous membranes in the forearm and lower leg distribute forces and maintain bone positions during activities. This stability is beneficial in weight-bearing areas or regions requiring controlled movement.