<s>[INST] I have a son who just turned 2 and he has a quarter sized lump that is very obvious when he bends his knee.  It doesn't cause him any pain or seem to affect his behavior at all.  I do have a doctor's appointment for him this afternoon.  Any thoughts or questions I should ask our doctor? [/INST] Thanks for your question on HCM. Knee joint lump can be due to any of the following. 1. Lipoma 2. Dermoid 3. Osteoma 4. Osteochondroma etc. All are benign swellings. So no treatment is required if it is not enlarging or painful or restrict knee joint movements. But better to consult orthopedic doctor and get done x ray of knee joint and ultrasound examination of knee joint to determine the cause  of swelling. If he is asymptomatic then no treatment is required. You need to wait and watch only. </s>