Physical Characteristics of Pseudoachondroplasia

Both the epiphyses and metaphyses are affected in pseudoachondroplasia. Clinically, it is recognized as a form of short-limbed dwarfism, with body proportions similar to those of achondroplasia, yet with normal-sized heads and facial features.

The postnatal onset of short-limbed growth deficiency will not become apparent until between 18 and 24 months of age. Pseudoachondroplasia manifests itself over time. Ultimately, adult stature is between 82 and 130 cm.

Face and Skull:

• Normal head size and facial features

Trunk, Chest and Spine:

• Disproportionately long trunk
• Prominent abdomen
• Exaggerated lumbar lordosis
• Possible thoracolumbar kyphosis
• Mild to moderate scoliosis

Arms and legs:

• Rhizomelic shortening of extremities
• Short, stubby fingers
• Incomplete elbow extension
• Delayed development of the femoral head, resulting in hip dysplasia and a waddling gait
• Genu varus or valgus angulation
• Severe ligamentous laxity (with exception of elbow)

What are the x-ray characteristics?

The radiographic features of pseudoachondroplastic patients include short and broad long bones with flaring of the metaphyses. Epiphyseal ossification is delayed. The epiphyses appear irregular and fragmented. The hips and knees are primarily affected. Due to their dysplastic nature, the carpals ossify late.

In the pelvis, the acetabulum (hip socket) is shallow and accentuates hip dysplasia. The triradiate cartilage is also late to mature and ossify. Arthrograms are helpful in identifying joint surfaces and planning surgery for angular deformities. The capital femoral epiphyses are small and irregular in children; in adults, there is marked dysplasia of the femoral head.The femoral head is flattened and fragmented. This leads to hip joint incongruity and exacerbates the effects of hip subluxation.

X-rays of the spine show platyspondyly and flame-shaped anterior projections. The interpedicular distance does not progressively decrease in the lumbar spine. In the neck, lateral x-rays of the cervical spine may reveal odontoid hypoplasia. The vertebrae will at first seem deformed, but the irregularities generally disappear by adolescence. Flexion-extension radiographs should be obtained to rule out atlantoaxial instability. MRI scans of the cervical spine (static, flexion/extension views and CSF flow studies) are helpful in identifying any compression of the spinal cord.