Changes in the Alignment of the Spine and Lower Limb in Children With Achondroplasia Treated With Vosoritide: A Single-center, 1-year Follow-up Prospective Study

BACKGROUND: Achondroplasia (ACH) is the most common skeletal dysplasia and is characterized by a short-limbed short stature, sagittal spinal malalignment, and genu varum. Vosoritide promotes longitudinal bone growth in children with ACH; however, its effects on various disease-specific complications, other than short stature, are unknown. This study aimed to investigate the therapeutic effects of vosoritide on spinal and lower limb malalignment in children with ACH. METHODS: This single-center, open-label, prospective study included patients with ACH aged younger than or equal to 15 years who received vosoritide treatment and had a minimum follow-up period of 1 year. To evaluate alignment after vosoritide treatment, radiologic parameters were measured from sagittal radiographs of the spine and anteroposterior radiographs of the bilateral lower limbs before the administration of vosoritide and 12 months after treatment. Paired t tests were used to compare parameters before and after vosoritide treatment. RESULTS: Seventeen patients (mean age, 7.6±2.7 y) were included. After 1-year treatment of vosoritide, the mean height increased by 5.4±1.3 cm. Changes in spinal alignment after 1 year of vosoritide treatment were 1.5 degrees for cervical lordosis, -1.3 degrees for thoracic kyphosis, -2.8 degrees for thoracolumbar kyphosis, -5.2 degrees for lumbar lordosis (LL), -2.2 degrees for pelvic tilt, -2.6 degrees for pelvic incidence, -0.4 degrees for sacral slope, and 2.6 mm for C7 sagittal vertical axis. Alignment changes in the lower limbs were -3.4 degrees for mechanical axis angle (MAA), 1.7 degrees for mechanical lateral proximal femoral angle (mLPFA), -2.8 degrees for mechanical lateral distal femoral angle (mLDFA), -0.2 degrees for medial proximal tibial angle, and -0.5 degrees for lateral distal tibial angle. The LL, MAA, mLPFA, and mLDFA levels showed statistically significant changes towards the normal range after treatment. CONCLUSIONS: One-year treatment of vosoritide decreased the exaggerated LL and improved genu varum deformity in children with ACH. Vosoritide therapy may not only increase longitudinal bone growth but also improve spinal and lower limb malalignment in children with ACH. LEVEL OF EVIDENCE: Level II: prospective comparative study.