Q. A 58-year-old woman with a known history of osteoarthritis comes to the clinic for pain and swelling behind her right knee for the past few weeks. She describes the swelling as more prominent when standing and says it feels tight and painful. Her vitals are normal. On physical examination, a fluid-filled mass of 2x2 cm is noted in the medial aspect of the popliteal fossa. The swelling becomes more prominent on full knee extension and softens when the knee is flexed to 45 degrees. Given these findings, what is the next step in management?