Synostosis (plural: synostoses) is fusion of two or more bones. It can be normal in puberty, 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. Source: Wikipedia (en)