Review Question - QID 8905

The child has achondroplasia with thoracolumbar kyphosis (TLK). Most kyphoses improve by 12-18 months of age as the child begins to walk and improve trunk strength.

Achondroplasia is the result of a chondrocyte FGFR-3 mutation affecting the proliferative zone of the physis. It arises as a de novo mutation in nearly 80% of patients, and is heritable in an autosomal dominant fashion. 50-100% of patients with achondroplasia are born with TLK, as well as other spinal abnormalities. The natural history of TLK is resolution in 90% of affected patients by the age of 18 months, corresponding with improvement in trunk strength and ambulation capacity. For patients with progressive, fixed kyphoses or those with neurologic manifestations, spinal fusion can be considered after the age of 4 years, allowing for the patient to grow large enough to accept instrumentation.

Shirley et al. reviewed achondroplasia. They note resolution of TLK as a result of the patient walking and gaining truncal strength. Bracing is initiated if TLK develops a fixed component >30 degrees, and surgery is reserved for patients with neurologic manifestations or fixed kyphosis >50 degrees.

Engberts et al. performed a systematic literature review to determine the true prevalence of TLK in children with achondroplasia. They concluded that the literature is sparse and inadequate to determine a true prevalence. Their search produced a prevalence between 50-100%.

Figure A is a seated lateral radiograph of the spine which shows kyphosis at the thoracolumbar junction.

Incorrect Answers:
Answer 1: TLK will tend to resolve by 18 months, but in rare cases can cause progressive and fixed deformities.
Answer 3: TLK tends to resolve by this time.
Answer 4: TLK is rarely fixed, and rarely progresses.
Answer 5: TLK should resolve prior to 6 years of age.