Clinical Manifestations. Growth retardation is usually not apparent until the child is 1 year old and often not until age 2 or 3. A delay in walking or an abnormal gait is often the first clinical clue. By this time, body measurements clearly reveal the disproportionate short stature. As the growth rate slows, the typical habitus of long trunk, exaggerated lumbar lordosis, prominent abdomen, and rhizomelic shortening of the limbs develops.

Head size and face are normal. By early childhood, the patient has a waddling gait. Malalignment of the knees develops, including bowleg, knock-knee, or windswept deformities (bowleg on one limb, knock-knee on the other). Flexion contractures develop in the hips and knees, with joint pain and precocious osteoarthritis. The hands and feet are short and stubby with considerable ligamentous laxity, particularly at the wrists and fingers. Cervical instability may also be identified. Incomplete elbow extension is typical and is related to the dysplastic bone changes rather than to soft tissue problems. Adult height ranges from 32 to 51 inches.

Radiographic Findings. The skull and facial bones are normal. The long bones in the hand appear short and stubby, and the carpals are dysplastic, with late ossification. In childhood, the small, irregular epiphyses of the femoral heads may become severely deformed and fragment by early adulthood. The ilia tend to be large and straight sided, whereas the pubic and ischial bones are short and broad; the greater sciatic notches are smaller than normal.

Spinal changes in childhood include moderate flattening of the vertebral bodies (platyspondyly) with biconvex deformity and irregularity of the superior and inferior growth plates, producing a tonguelike projection apparent on the lateral view. By adolescence, most of these characteristic vertebral changes disappear and only mild platyspondyly persists. Scoliosis and excessive lumbar lordosis may also be evident.