The rate at which cartilage cells in the growth plates of the long bones turn into bone is slow, leading to short bones and reduced height. A child with achondroplasia has a relatively normal torso and short arms and legs. The upper arms and thighs are more shortened than the forearms and lower legs. Teeth may be crowded and upper and lower teeth may be poorly aligned. The lower legs may become bowed, and feet are generally short, broad and flat.
Hands are short with stubby fingers.
Because of the large head, short arms and legs, poor muscle tone and loose joints, a baby with achondroplasia is slow to sit, stand and walk alone. This sometimes causes people to think the child is mentally retarded, but most children with achondroplasia have normal intelligence. Other complications include frequent middle ear infections that can cause mild to moderate hearing loss. Low back and leg pains are common, especially in adults, partly because there is pressure on the spinal cord from a small spinal canal. This pressure on the spinal cord also can cause paralysis of the legs, requiring surgery to relieve the pressure.