Discoid Lateral Meniscus

A 12-year-old female competitive gymnast presents with a 3-month history of recurrent lateral knee pain, popping, and snapping during tumbling. On examination, she has a positive McMurray test for the lateral meniscus with an audible clunk at 20° of flexion during varus stress. MRI shows the structure marked **A** on coronal images covering most of the lateral tibial plateau, with more than three continuous bow-tie sagittal segments measuring >15 mm. Plain radiographs demonstrate Watanabe signs including widening of the lateral joint space and squaring of the lateral femoral condyle. What is the most appropriate diagnosis and initial management?