Achondroplasia is the most common type of short-limb (rhizomelic) dwarfism with the primary defect being abnormal endochondral bone formation. There is normal periosteal and oppositional bone growth. It is an autosomal dominant trait with at least 80% of cases being new random mutations. The condition has an incidence of 1:26,000 - 66,000 births.

Neonatal radiographs of the axial and appendicular skeleton demonstrate various classic findings. The base of the skull which is formed by endochondral ossification is shortened with a small foramen magnum. There is a concurrent frontal bossing. The interpedicular distances of the lumbar spine show progressive narrowing in the caudal direction. An exaggerated lumbar lordosis is present once walking begins. In addition, there are shortened pedicles and posterior vertebral body scalloping. The pelvis demonstrates flattened iliac wings with a characterisitc "champagne glass" appeareance along with a short sacrosciatic notch and decreased acetabular angle. The long bones have metaphysical flaring. The distal femoral physes may have an inverted-V configuration. The hands exhibit brachydactyly.