Skeletal dysplasia (also known as osteochondrodysplasia) refers to any abnormality in bone formation. There is a very wide clinicopathological spectrum and any part of the skeleton can be affected.
The overall prevalence is estimated at ~2 per 10,000 live births .
At least 32 groups with more than 350 distinct entities have been described . One way of broadly classifying them is into limb deficiency, limb shortening/dysplastic or non-limb shortening types. Another way of categorizing is by whether the dysplasia is sclerosing or non-sclerosing.
- amelia: complete limb absence
- meromelia: partial limb absence
Rhizomelic dwarfism is characterized by limb shortening, being most notable proximally:
- achondroplasia (most common short-limbed dwarfism)
- thanatophoric dysplasia
- osteogenesis imperfecta
- rhizomelic chondrodysplasia punctata
- asphyxiating thoracic dysplasia (Jeune disease)
- non-rhizomelic chondrodysplasia punctata: Conradi-Hunermann syndrome
- diastrophic dysplasia
- campomelic dysplasia
- chondroectodermal dysplasia / Ellis-van Creveld syndrome
- Kniest dysplasia
- spondyloepiphyseal dysplasia
- multiple epiphyseal dysplasia: mild limb shortening
- metaphyseal chondrodysplasia
- Schmid type
- Pena and Vaandrager type
- Jansen type
- McKusick type
- Pyle disease: metaphyseal dysplasia
- progressive diaphyseal dysplasia: Camurati-Engelmann disease
- more to be added
Skeletal dysplasias are usually diagnosed on antenatal ultrasound or after birth on the basis of clinical features and radiography. There are a wide variety of radiographic features and these are discussed separately.
Although no single unifying features exist, Mahony has proposed an evaluation of the following sonographic parameters and questions, which are helpful to achieve a precise diagnosis:
- what is the degree of bone shortening?
- the severity of bone shortening varies from extreme (many standard deviations below the mean, at least 5-6 weeks below expected length for gestational age, with the limbs oriented at approximately right angles to the fetal trunk) to mild-to-moderate (with a more normal orientation of the limbs to the fetal trunk)
- what is the distribution of involvement?
- rhizomelic, mesomelic, or acromelic bone shortening occurs with different dysplasias
- are bone fractures or extremity bowing present?
- what is the degree and distribution of ossification?
- what is the calvarial configuration?
- what is the thoracic size?
- a small thorax indicates a high probability of pulmonary hypoplasia, but the thoracic shape often does not assist in rendering a specific diagnosis
- rib fractures with a bell-shaped thorax usually indicates osteogenesis imperfecta
- is polydactyly present?
Treatment and prognosis
The prognosis is widely variable, ranging from being lethal to very mild cosmetic deficits.