A fibrous joint refers to an articulation between two or more bones in the human body. Unlike synovial or movable joints like the shoulder or knee, fibrous joints permit little to no movement between bones. Made up of tough connective tissue like the kind making up ligaments and tendons, the fibrous joint contains mostly collagen linking the bones together. Examples of fibrous joints, of which there are three types, include the junctions between the bones of the cranium or skull, those between the parallel long bones in the lower leg, and those between the teeth and the jawbones.
The type of fibrous joint found in the skull — the only joint of its type in the body — is known as a suture. These are the long, jagged joints that resemble cracks in pavement connecting the curved bones of the cranium: the frontal, parietal, temporal, and occipital bones. At birth, there are small gaps between the bones at the sutures that allow for very slight expansion and contraction as the skull takes its shape.
As the skull develops, however, in early months of life, these gaps close and the joints become synarthrodial, meaning that they do not allow movement other than a slight elasticity. The specific fibers binding the bones of the skull are known as Sharpey’s fibers. These are not linear but rather are crisscrossed to allow very slight flexibility in several directions.
Another type of fibrous joint is the syndesmosis, the joint type found between the tibia and fibula in the shin, as well as between the radius in the forearm and carpal bones in the wrist. The tibia and fibula are long bones that lie side by side. The syndesmosis is found where the distal or lower ends of the tibia and fibula meet above the ankle and is referred to as the inferior tibiofibular articulation. At the wrist, the syndesmosis is the radiocarpal joint, which is where the long radius bone in the arm meets the clustered, irregularly shaped carpal bones at the base of the hand. Both joints allow only minor movement and are joined by a strong ligament between the bones called an interosseous ligament.
A third type of fibrous joint is the gomphosis, another joint type that is found in only one location in the body. Gomphoses are the joints attaching the teeth by their roots to either the maxillary bone in the top row or the mandible in the bottom row. The teeth are held in place against their respective jawbones within sockets called alveoli by the periodontal ligaments. These ligaments are very tiny and do not permit any real movement — only a gradual shifting as produced by the wearing of braces or a retainer.