Synchondroses

Synchondrosis is a type of cartilaginous joint in which two or more bones are joined by hyaline cartilage. It is considered a primary, or temporary, joint in contrast to the secondary cartilaginous joints known as symphyses, which are bridged by fibrocartilage. In a synchondrosis the hyaline cartilage provides a rigid yet growth-supporting link, allowing longitudinal bone growth during development. Most synchondroses are later replaced by bone, resulting in a synostosis as growth ceases.

Common examples include the epiphyseal (growth) plates of long bones, where the metaphysis and epiphysis are separated by a plate of hyaline cartilage during growth. The skull base contains several synchondroses, the best known being the spheno-occipital synchondrosis, which ossifies in late adolescence. The first sternocostal joint between the first costal cartilage and the sternum is another classic example of a synchondrosis. In the developing skeleton, other costal-cartilage interfaces can also exhibit synchondrotic connections.

Development and clinical significance: Because they permit longitudinal growth, synchondroses play a crucial role in skeletal development. Ossification progresses with age, and a synchondrosis typically becomes a bony synostosis as growth finishes. Timing and pattern of fusion vary by site and individual. Clinically, persistent or abnormal fusion of synchondroses can influence craniofacial or somatic growth, and radiographic evaluation must distinguish normal developmental synchondroses from fractures or other pathology, especially in children and adolescents.