CASE                               30                               

A 1-year-old male is brought to your clinic by his parents for evaluation. He has shortened limbs with the proximal aspects more involved than the distal aspect, frontal bossing, and midface hypoplasia. He cannot bring his middle and ring fingers together, and he has genu varum. His feet are not clubbed.

The mutation responsible for his skeletal dysplasia causes a defect in what gene?

1. CBFA-1

2. Sulfate transporter

3. COMP

4. EXT1

5. FGFR-3

Discussion

The correct answer is (E). The patient has achondroplasia— the features described above are consistent with this diagnosis (rhizomelic shortening of the limbs, frontal bossing with midface hypoplasia, trident hands, and genu varum). FGFR-3 is the gene affected in achondroplasia. The mutation inhibits chondrocyte proliferation in the zone of proliferation of the growth plate. CBFA-1 is the gene affected in cleidocranial dysplasia. Although there is frontal bossing with cleidocranial dysplasia, the other features of that condition are not present with this patient. The sulfate transporter gene is affected in diastrophic dysplasia. This condition also has short stature with rhizomelic shortening of the limbs, the hand deformity is a hitchhiker thumb rather than a trident hand, the ears are described as “cauliflower” ears, and the feet are clubbed. Mutations in COMP result in pseudoachondroplasia. Given the face abnormalities, this patient does not have pseudoachondroplasia as it is associated with normal facies. EXT1 is involved in multiple hereditary exostosis.

On examination, you notice that when he is sat up, he has kyphosis of his thoracolumbar spine. What is your recommendation for treatment of this?

1. Observation

2. Traction

3. Casting

4. Surgical decompression with stabilization via a growing rod construct

Discussion

The correct answer is (A). Thoracolumbar kyphosis is seen in many children with achondroplasia. It is thought to be related to hypotonia of the core muscles combined with a relatively large head. It usually resolves when the child begins walking. The other options are incorrect because they are unnecessary in the setting of a condition that usually self-resolves. The spine condition to be aware of in the growing child and adult with achondroplasia is the decreased interpedicular distance in the lumbar vertebrae and lumbar stenosis with short pedicles.

There has been some concern of sleep apnea for this child. what should the orthopaedic surgeon order (if not already ordered by others previously) in children with achondroplasia, particularly when there are apnea issues?

1. Pulmonary function tests

2. Chest x-ray

3. MRI of the chest

4. MRI of the base of brain and cervical spine

5. ENT consult

Discussion

The correct answer is (D). In a child with achondroplasia there is a need to screen for foramen magnum and upper cervical spine stenosis. Should these be present, they can cause central sleep apnea and lead to sudden death.

Objectives: Did you learn...?

The clinical findings associated with achondroplasia? The gene affected in patients with achondroplasia?

The appropriate management of thoracolumbar kyphosis in this population? Importance of screening for foramen magnum stenosis?