Neoplasms can occur in the bones, bone marrow, cartilage, synovium(lining) and soft tissues of the knee joint as in any other part and organ of the body. They produce swelling, pain and loss of movement in the advanced stage but earlier on there may be no finding and a limp may be the only complaint

Symptoms-
Pain. The pain may be brought about by an injury, when the neoplasm has been there already. The pain may not be of any specific nature. .Swelling. .Loss of movement. Sometimes the neoplasms can be discovered on x-rays taken for some other purpose like injury. Sometimes it may be difficult to diagnose neoplasms inside the joint as they mimic arthritis and even senior orthopaedic surgeons may attribute a swelling from a joint in a middle aged person to a chronic form of arthritis like osteoarthritis.

Investigations and Treatment
X-rays maybe informative if the neoplasm is involving the bones and has destroyed them. Inserting a needle inside the joint and examining the fluid withdrawn may be informative. The normal knee has a small amount of yellowish fluid. In certain soft tissue tumours, the fluid may be voluminous and brown like altered blood. MRI or CT Scan are very useful to pick up tumours earlier. consists of clearing the diseased tissue and restoring the continuity of the limb if possible. If it is not possible to radically remove diseased tissue an amputation may be required.

Treatment
Clearing the diseased tissue and restoring the continuity of the limb if possible. Custom made mega prostheses can help in limb reconstruction after radical excision of the tumor. If it is not possible to radically remove diseased tissue an amputation may be required.