Welcome to health care magic. 1.The features with history suggest that most possible cause would be ganglion ( a fluid collation cystic structure). 2.Which arises from the joint space entities - tendon, bursa, nerve sheet, cartilage, ligament. 3.The next step in this is they are general slow growing pain less lumps - one has to monitor the growth. 4.If any discomfort or pressure effect seen at the joint area - a small incision and drainage followed by an course of antibiotics is necessary. 5.An ultrasound scan will be good to evaluate the nature of the lesion and its source and extension, But best tool will be MRI for knee joint and adjacent structures - good luck. Hope i have answered your query. Any thing to ask do not hesitate. Thank you.