Synostosis

Synostosis (from Ancient Greek συν- (syn-) 'together' and ὀστέον (ostéon) 'bone'; plural: synostoses) is fusion of two or more bones. It can be normal in puberty (e.g. fusion of the epiphyseal plate to become the epiphyseal line), or abnormal. When synostosis is abnormal it is a type of dysostosis. Examples of synostoses include:

• craniosynostosis – an abnormal fusion of two or more cranial bones;
• radioulnar synostosis – the abnormal fusion of the radius and ulna bones of the forearm;
• tarsal coalition – a failure to separately form all seven bones of the tarsus (the hind part of the foot) resulting in an amalgamation of two bones; and
• syndactyly – the abnormal fusion of neighboring digits.

Synostosis within joints can cause ankylosis.