A 9-year-old girl presents with a 6-month history of progressive mid-back pain, worse with exercise, and relieved with rest. She has no history of trauma. On physical examination, she has a rigid kyphosis with a sharp angulation when she bends over. The curvature does not flatten with forward bending, extension, or lying supine. She has no neurological findings. X-rays of the spine reveal vertebral wedging and narrowing of the intervertebral disc spaces, with an angular deformity of the thoracic spine and a Cobb angle of 71°. Which of the following is the most appropriate next step in management?