What are the physical characteristics of Achondroplasia?

Achondroplasia causes disproportionate short stature. Specifically the limbs are disporportionately small when compared to the trunk. Within the limbs the proximal segment is shorter causing rhizomelia. The average adult height is 42" in men and 4 in women with achondroplasia. Achondroplasts have average intelligence and can lead very rich and productive lives.

This picture shows twin brothers. The twin on the right has achondroplasia.

Here are other characteristics which can be seen in patients with achondroplasia:

Face and Skull:

The head circumference may be larger than average.
The forehead tends to be prominent. This is termed frontal bossing.
The nasal bridge tends to be depressed and the nostrils are upturned.
The mid-face is underdeveloped, which is termed maxillary hypoplasia.
The foramen magnum, which is the opening in the skull base through which the spinal cord passes is smaller then average.

Trunk, Chest and Spine:

Thoraco-lumbar kyphosis (TLK) is present in most infants with achondroplasia and is a normal finding. It can be seen represented in the drawing on the right as the prominence in the lower back(5).
The TLK is replaced in later childhood by lumbar lordosis or sway back.
TLK is thought to be caused by the large head size and poor muscular tone in children who are not yet walking. It improves without treatment in 90% of affected children as they begin to walk.
The chest usually is broad and flat. The abdomen and buttocks are prominent.
The spinal canal is smaller than average in achondroplasia

Arms and legs:

There is marked ligamentous laxity or loose joints.
Despite the loose joints, typically the elbows cannot be fully extended. Less commonly the elbow joint may be out of place. This rarely causes symptoms or loss of function.
In infancy and early childhood there is extra space between the 3^rd and 4^th fingers. This is termed trident hand and disappears spontaneously in later childhood. The drawing below demonstrates the trident (5).
The fingers are short and broad giving rise to a stubby appearance.

Trident Netter

What are the x-ray characteristics?

Long bones are relatively plump and short. Proximal humerus and femur in infancy have distinctive rectangular or translucent ovals that change by 2 years. Fibulas tend to be longer than tibias.

Spacing between vertebral pedicles decreases rather than increases in the lumbar spine as you move from head to pelvis.

A short, broad pelvis with wide, non-flaring iliac wings.