The skeletal system

Skeletal dysplasias are a group of disorders with a disturbance in development and or growth of cartilage and/or bone. Epiphysis, metaphysis and/or diaphysis of long bones are affected in a generalised manner with or without involvement of membranous bone of the skull. A dysostosis affects one or some skeletal elements while the other bones remain normal. There are approximately 450 different disorders known with involvement of the skeleton. Some 50 dysplasias are lethal. Lethality is usually based on thoracic underdevelopment and lung hypoplasia. The overall frequency among stillbirths and liveborns has been estimated to be 1 per 4000 to 1 per 6000 births and the frequency among perinatal deaths to be 1 per 110 deaths. Classification of skeletal dysplasias is based on the localisation of the affected bony structure; the diagnosis is made primarily on radiological features.