A 16-year-old competitive gymnast presents with chronic lower back pain exacerbated by hyperextension. Lateral X-ray of the lumbar spine shows a bilateral defect in the structure marked **C** (pars interarticularis) at the L5 level, with the classic "Scottie dog" appearance where the defect appears as a collar around the dog's neck. There is no forward slip of L5 on S1 at this time. Which of the following best describes the patient's current spinal pathology and the most appropriate initial management?