Arthritis of the knee is a very common problem.  There are three main conditions that cause arthritis of the knee; Osteoarthritis, Rheumatoid arthritis and post-traumatic arthritis.  Osteoarthritis occurs when the protective cartilage over the bones wears down.  Rheumatoid arthritis is an auto-immune inflammatory disease that affects  the lining of the joints causing painful swelling.  Other less common causes include collagen vascular diseases, infection and villonodular synovitis.  The pain of arthritis of the knee is usually confined to the area of the knee joint.  The pain usually develops gradually.  It is worse with movement or activity of the joint.  Over time, simple activities such as walking can prove difficult. As the patient uses the knee less over time, muscle wasting may occur.  X-rays, MRIs and CT scans are all useful in delineating the extent of the problem.  Blood work may look for infectious causes or autoimmune disorders such as rheumatoid arthritis.  Treatment begins with conservative modalities including rest, alteration in activities, heat, ice and physical therapy.  Nonsteroidal anti-inflammatory medications are useful to decrease the pain and swelling.  Alternative medications such as glucosamine and chondroitin may be useful.  Injection into the joint of a corticosteroid may relieve pain acutely but may not be effective over the long term.  Viscosupplementation with hyaluronic acid has been tried as has injection of gold salts.  For severe cases, arthroscopic knee surgery or knee joint replacement may be a last resort.