synarthrosis

Synarthrosis is a type of joint defined by an absence of measurable movement. It is one of the functional classifications of joints, alongside amphiarthrosis (slightly movable) and diarthrosis (freely movable). In a synarthrosis, the bones are tightly bound and motion is highly restricted under normal conditions. These joints are typically connected by fibrous or cartilaginous tissue, producing a rigid union.

Structurally, synarthroses are usually fibrous or cartilaginous. Fibrous synarthroses include sutures, which connect most skull bones with dense connective tissue, and gomphoses, where a tooth is anchored in its socket by surrounding tissues. Cartilaginous synarthroses, or synchondroses, join bones by hyaline cartilage, such as certain temporary joints between growing bones and some rib-sternal connections in early life. Over time, many synchondroses may ossify and become synostoses, resulting in a bone-to-bone, immobile junction.

Developmental and clinical notes are relevant to synarthroses. Skull sutures allow growth of the brain during infancy and childhood and progressively fuse with age to form a rigid cranial vault. Premature fusion of sutures, a condition known as craniosynostosis, can alter skull shape and brain development. Gomphoses securing teeth typically remain functionally immobile in adults, though pathology affecting the surrounding structures can influence dental health. Overall, the immobility of synarthroses contributes to skeletal stability but can be involved in age-related changes or specific clinical conditions.