A 12-year-old girl presents with 6 months of moderate but persistent lower back pain. She has increased pain when she stands upright on one leg as well as shooting pain when she tries to bend down to touch her toes. A straight leg raise test is negative but it is noted that her hamstrings are tight. She has tried NSAIDs and PT, which have provided her with limited relief. Upright radiographs are shown in Figure A. What is the next most appropriate treatment?