構造的ジョイント：繊維性ジョイント

Fibrous joints are classified into three types: syndesmoses, sutures, and gomphoses. Syndesmoses are slightly movable joints connected by ligaments or interosseous membranes, such as those between the tibia and fibula. Sutures are immovable joints found only in the skull, where bones are connected by short connective tissue fibers. Gomphoses are immovable peg-and-socket joints that exist only between teeth and their bony sockets.

In syndesmoses, movement depends directly on ligament length. The longer the ligament, the more movement is possible between the bones. For example, the joints between the radius and ulna in the forearm and between the tibia and fibula in the leg are syndesmoses where ligament length determines the degree of mobility allowed at these articulations.

Skull sutures are immovable joints because bones are connected by short, dense connective tissue fibers that form a tight, convoluted union. In adults, the skull bones are closely opposed with fibrous connective tissue filling the narrow gap between them. This tight arrangement prevents most movement between bones and provides stability to protect the brain while forming the face.

Periodontal ligaments are short bands of dense connective tissue that span between the bony walls of dental sockets and tooth roots. These ligaments fix the roots of teeth into the dental sockets of the maxilla and mandible, anchoring teeth firmly in place. Gomphoses are classified as immovable joints due to the strong attachment provided by these periodontal ligaments.

An interosseous membrane is a broad sheet of fibrous connective tissue that fills the wide gap between parallel bones in syndesmoses. It is found in the forearm between the radius and ulna and in the leg between the tibia and fibula. This membrane strongly unites the bones while allowing limited movement, making it a key structural component of these fibrous joints.

Fibrous joints lack a synovial cavity, distinguishing them from synovial joints. They are formed entirely by fibrous connective tissue connecting the bones, providing stability with minimal to no movement. Unlike structural joints synovial joints, which have fluid-filled cavities and allow greater mobility, fibrous joints prioritize bone stability and protection through direct tissue connection.

Gomphoses are specialized fibrous joints located exclusively between teeth and their bony sockets in the maxilla and mandible. Also called peg-and-socket joints, they are unique because they anchor tooth roots into bone through periodontal ligaments. This specialized design makes gomphoses functionally immovable, providing the stability necessary for teeth to withstand chewing forces.