Knee Pain

Get a Leg Up on Knee Pain
by Dennis Armstrong, M.D.

An incredible feat of engineering, the knee is one of the most complicated and moveable joints in the body. Not only does it bend and straighten like a simple hinge joint, it can also rotate; in fact, the knee has one of the widest ranges of motion of any joint.

The knee is where the femur (thigh bone) and tibia (shin bone) come together. A third bone, the triangular-shaped patella (kneecap), lies across the front of the joint to protect it. As in our other joints, a layer of protective cartilage covers the ends of the bones to allow for smooth movement. Additionally there are the medial meniscus and the lateral meniscus, which add more protection. The entire joint is encased in a capsule lined with a membrane called the synovium that produces fluid to lubricate the joint. Various ligaments support the knee and prevent excess side-to-side movement. Two ligaments called cruciate ligaments (from the Latin word "crux," meaning cross) cross over each other as they run diagonally between the femur and tibia; they help prevent overbending and overstraightening of the knee.

Causes of Knee Pain

Considering the complicated way the knee is put together, there are many things that can cause knee pain. The knee is susceptible to damage from repetitive weight-bearing activity, such as running or jogging, and a variety of sports injuries. Movements such as coming to a quick stop, changing directions, pivoting or landing from a jump can injure the knee's ligaments. Athletes often rupture their anterior cruciate ligament, for example. When a cruciate ligament is sprained or ruptured, the knee joint loses some of its stability and may become painful. When the meniscus is torn, small fragments of cartilage can loosen and catch between the surfaces of the femur and tibia, causing pain, limiting knee movement and at times causing instability.

As a weight-bearing joint, the knee is one of the primary joints affected by arthritis. Both osteoarthritis (OA) and rheumatoid arthritis (RA) can damage the smooth cartilage and decrease the space between the femur and tibia. Eventually, so much cartilage may be eroded that bone rubs on bone, causing a great deal of pain and limiting your ability to walk, climb stairs and participate in everyday activities.

Swelling also frequently affects the knee, and can have many causes. Fluid can accumulate in the bursae (a bursa is a sac filled with a gel-like, fluid material that lies between a tendon and a bone and acts as a buffer for the tendon to work across). For example, injury or excessive kneeling can cause the bursa located in front of the kneecap to become inflamed and fill with fluid, resulting in what was once commonly called "water on the knee."

These x-rays show how degenerative arthritis in the knee joint causes bone to rub on bone, resulting in pain and loss of function. (The image at left is a side view; at right is a frontal view.

   In patients with some type of arthritis, particularly rheumatoid arthritis, the synovium (joint lining) may produce excess synovial fluid. This is called an effusion, and it makes the joint red, warm and swollen. Blood can also accumulate in the knee as a result of injury or certain diseases, such as hemophilia.

  Several disorders affect the kneecap. It can be fractured or dislocated due to a direct blow; congenital abnormalities may also cause dislocation. Retropatellar arthritis, an inflammation of the underside of the kneecap, causes a roughening of that surface and causes pain that worsens when you bend your knee or climb stairs.

  There are many other possible causes of knee pain, too many to go into here. By evaluating your symptoms, conducting a physical exam and ordering diagnostic tests such as blood work and x-rays, the doctor will determine the cause of your knee pain.

Managing Knee Pain

   The key to successful treatment of your knee pain is to obtain the correct diagnosis. Once that's accomplished, you and your physician can work on designing the treatment plan that's right for you, starting with conservative measures.
Non-steroidal anti-inflammatory medications (NSAIDs)--aspirin, ibuprofen, Naprosyn, etc.--are the first line of defense against pain and inflammation in the knee joint, whether the cause is a sports injury or arthritis. In the case of rheumatoid arthritis, when both knees are painful and inflamed, a disease-modifying medication may be prescribed to try to slow down further damage to the joint. Physical therapy, heat and cold, rest, exercise and use of assistive devices such as canes are some of the other conservative methods that may be effectively employed.

  Several surgical procedures also can help relieve pain and restore mobility to the knee joint. For a torn ligament or a tear in the meniscus, your doctor may suggest a minimally invasive procedure called arthroscopy. Through small incisions, the surgeon inserts a tubular instrument called an arthroscope, complete with a light and camera, into the joint capsule. An image of the inside of the joint is projected onto a monitor in the room. Once the nature of the problem is determined--a loose cartilage fragment, for example--the surgeon can use another small instrument to cut and remove the fragment. All this can be done without a large incision, or a hospital stay. Recovery is also much faster than with traditional surgery.

  Another procedure is synovectomy, the removal of diseased or damaged tissue from inside the joint. This is often used in patients with rheumatoid arthritis, and can be done traditionally or arthroscopically. A procedure called osteotomy involves trimming and repositioning the leg bones to obtain a better weight distribution across the knee, slowing damage caused by osteoarthritis and relieving pain.

  When more conservative treatments have not provided adequate relief, total joint replacement may be recommended. Total knee replacement is a major surgical procedure that replaces the weight-bearing surfaces of the femur and tibia, as well as the underside of the kneecap, with durable metal and plastic components. Pain relief is often immediate and dramatic, and the success rate for total knee replacement, like total hip replacement, is quite high. On average, 90+ percent of knee replacements are still going strong 15 years after the surgery. Research continues into developing new materials and implant designs that will last even longer. More than 100,000 knee replacements are performed in this country annually.

  Patients with severe knee damage who are not candidates for knee replacement may undergo knee fusion; while this greatly reduces your ability to move the joint, at least it allows pain-free weight bearing.

  If you suffer from knee pain and don't know what's causing it, I encourage you to see your doctor for an accurate diagnosis and appropriate treatment plan. Not only can painful knees limit your activities, they can also have a negative effect on your overall health. If your knees hurt, you aren't going to walk or get the cardiovascular exercise your heart needs. So the earlier your knee pain is diagnosed and treated, the better your quality of life will be in the long run.

About the author:
Dennis Armstrong, M.D. graduated from the Wayne State School of Medicine and completed his orthopaedic residency at Henry Ford Hospital in Detroit, Michigan. Dr. Armstrong is board certified in orthopaedic surgery and specializes in arthritis reconstructive surgery. He has been involved in several clinical investigative studies researching the surgery and care of those undergoing total joint replacement, and has authored numerous papers and provided multiple presentations on his clinical research.