They are also referred to as the synarthroses. These joints are fixed, immovable, and they have no cavity. The dense fibrous tissue that connects the sutures is made mostly out of collagen. These joints are synarthroses ( immovable joints). A tiny amount of movement is permitted at sutures, which contributes to the compliance and elasticity of the skull. There are six such classifications: hinge (elbow), saddle (carpometacarpal joint), planar (acromioclavicular joint), pivot (atlantoaxial joint), condyloid (metacarpophalangeal joint), and ball and socket (hip joint).Ĭopyright © 2022, StatPearls Publishing LLC.Sutures are bound together by a matrix of connective tissues called Sharpey’s fibers, which grow from each bone into the adjoining one. Synovial joints are often further classified by the type of movements they permit. Some synovial joints also have associated fibrocartilage, such as menisci, between articulating bones. The articular cartilage and the synovial membrane are continuous. Hyaline cartilage forms the articular cartilage, covering the entire articulating surface of each bone. The joint cavity contains synovial fluid, secreted by the synovial membrane (synovium), which lines the articular capsule. The cavity is surrounded by the articular capsule, which is a fibrous connective tissue that is attached to each participating bone just beyond its articulating surface. Its joint cavity characterizes the synovial joint. Synovial joints are freely mobile (diarthroses) and are considered the main functional joints of the body. These joints are slightly mobile (amphiarthroses). The secondary cartilaginous joint, also known as symphysis, may involve either hyaline or fibrocartilage. The joint between the epiphysis and diaphysis of growing long bones is an example. These joints may be slightly mobile (amphiarthroses) or immobile (synarthroses). Primary cartilaginous joints, also known as synchondroses, only involve hyaline cartilage. Depending on the type of cartilage involved, the joints are further classified as primary and secondary cartilaginous joints. In cartilaginous joints, the bones attach by hyaline cartilage or fibrocartilage. For example, the tibia connects to the fibula, forming the middle tibiofibular joint, and the ulna attaches to the radius, forming the middle radio-ulnar joint. In syndesmosis joints, the two bones are held together by an interosseous membrane. Syndesmoses are slightly movable joints (amphiarthroses). The periodontal ligament is the fibrous tissue that connects the tooth to the socket. Gomphoses are the immobile joints between the teeth and their sockets in the mandible and maxillae. Eventually, cranial sutures ossify- the two adjacent plates fuse to form one bone this fusion is termed synostosis. As the skull enlarges, the fontanelles reduce to a narrow layer of fibrous connective tissue, called Sharpey’s fibers, that suture the bony plates together. This initial flexibility allows the infant’s head to get through the birth canal at delivery and permits the enlargement of the brain after birth. The plate-like bones of the skull are slightly mobile at birth because of the connective tissue between them, termed fontanelles. Sutures are immobile joints in the cranium. They are subdivided further into sutures, gomphoses, and syndesmoses. Fibrous joints are usually immoveable (synarthroses) and have no joint cavity. The two classification schemes correlate: synarthroses are fibrous, amphiarthroses are cartilaginous, and diarthroses are synovial.Ī fibrous joint is a fixed joint where fibrous tissue comprised primarily of collagen connects bones. Functionally the three types of joints are synarthrosis (immovable), amphiarthrosis (slightly moveable), and diarthrosis (freely moveable). Histologically the three joints in the body are fibrous, cartilaginous, and synovial. Joints can be classified either histologically on the dominant type of connective tissue functionally based on the amount of movement permitted. A joint is a point where two bones make contact.
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