Review Question - QID 5431

The patient has thoracolumbar kyphosis in association with achondroplasia. This disease involves an FGFR3 mutation. While in most cases the mutation arises spontaneously, once present, it is transmitted in an autosomal-dominant pattern.

Achondroplasia is caused by a mutation in the FGFR3 gene on chromosome 4 leading to enhanced tyrosine kinase activity. The disease pattern is characterized by rhizomelic, disproportionate shortening of the limbs, short stature, frontal bossing, midface hypoplasia, foramen magnus stenosis, spinal stenosis and thoracolumbar kyphosis.

Thoracolumbar kyphosis develops in most infants with achondroplasia as a flexible deformity thought to be due to forward slouching with unsupported sitting. It may be associated with anterior vertebral wedging in advancing cases. In approximately 70% of cases, this deformity corrects spontaneously by age 3 without operative treatment. Bracing is controversial, though sometimes implemented at kyphotic angles above 30 degrees.

Shirley et al review the genetics, clinical presentation, and management of achondroplasia. They discuss foramen magnum stenosis, thoracolumbar kyphosis, lumbosacral hyperlordosis, spinal stenosis, and extremity deformities. Regarding thoracolumbar kyphosis they report an average 20 degree curve at birth, typically T10 to L4 levels. Frequency over time decreases from 87% at 1year to 11% at ages 5-10.

Engberts et al present a study on the prevalence of thoracolumbar kyphosis in achondroplasia. They perform a meta-analysis of 7 studies but due to population differences and little information on deformity measurement methods they conclude only that prevalence is likely between 50-100%.

Misra et al provide a review specifically of thoracolumbar deformity in achondroplasia, discussing presentation, spine development, and non-operative as well as operative management of the deformity. In addition to a review of thoracolumbar kyphosis, they state that the Type 3 FGFR is one affecting late development, particularly that of maturing chondrocytes. This they say, is part of the reason there is an effect on both limbs and spine development.

Figure A shows a lateral spine radiograph of a 13-month-old child with achondroplasia and thoracolumbar kyphosis. Illustrations A and B show thoracolumbar kyphosis in a 15-month-old patient before (A) and after (B) TLSO brace application.