What is the most common type of dwarfism, and what are its manifestations?
The most common type of dwarfism is achondroplasia. This is a rhizomelic (shortening of the proximal bones) autosomal dominant disorder. Typical characteristics include a large head with frontal bossing, a trident configuration of the hands, genu varum (bowed legs), and an exaggerated lumbar lordosis (with posterior scalloping of the vertebral bodies). On a frontal radiograph of the lumbosacral spine in a normal patient, the distance between the pedicles gradually widens from L1 to L5, whereas an achondroplastic dwarf shows a decrease in the interpedicular distance of the caudal spine. Other radiographic findings include a notch-like sacroiliac groove and metaphyseal flaring of the long bones.