Introduction
Knee pain is a common reason that people visit their doctors' offices or the emergency room. Often, knee pain is the result of an injury, such as a ruptured ligament or torn cartilage. But some medical conditions can also bring you to your knees, including arthritis, gout and infections.

Depending on the type and severity of damage, knee pain can be a minor annoyance, causing an occasional twinge when you kneel down or exercise strenuously. Or knee pain can lead to severe discomfort and disability.

Many relatively minor instances of knee pain respond well to self-care measures. More serious injuries, such as a ruptured ligament or tendon, may require surgical repair.

A knee injury can affect any of the ligaments, tendons or fluid-filled sacs (bursa) that surround your knee joint as well as the bones, cartilage and ligaments that form the joint itself. Because of the knee's complexity, the number of structures involved, the amount of use it gets over a lifetime, and the range of injuries and diseases that can cause knee pain, the signs and symptoms of knee problems can vary widely.

Acute Knee Pain
Severe knee pain that comes on suddenly (acute pain) is often the result of injury. Some of the more common knee injuries and their signs and symptoms include the following:

• Ligament Injuries. Your knee contains four ligaments — tough bands of tissue that connect your thighbone (femur) to your lower leg bones (tibia and fibula). You have two collateral ligaments — one on the inside (medial collateral ligament) and one on the outside (lateral collateral ligament) of each knee. A tear in one of these ligaments, usually the result of a fall or contact trauma, is likely to cause immediate pain in the injured area.

• The other two ligaments are inside your knee and cross each other as they stretch diagonally from the bottom of your thighbone to the top of your shinbone (tibia). The posterior cruciate ligament (PCL) connects to the back of your shinbone, and the anterior cruciate ligament (ACL) connects near the front of your shinbone. If you tear the ACL, either partially or completely, you're likely to know it right away. You may feel or hear a pop in your knee and have intense pain and immediate swelling. When you try to stand and put weight on your injured leg, your knee may "buckle" or at least feel as if it might give way.

• PCL tears aren't usually as dramatic or painful. Most often, you'll experience pain and swelling in the space behind your knee (popliteal fossa) and a feeling of instability, as if your knee might give way.

• Tendon Injuries (Tendinitis). Tendinitis is irritation and inflammation of one or more tendons — the thick, fibrous cords that attach muscles to bone. Athletes — especially runners, skiers and cyclists — are prone to develop inflammation in the patellar tendon, which connects the quadriceps muscle on the front of the thigh to the larger lower leg bone (tibia). Tendinitis can occur in one or both knees and often causes pain and swelling at the front of your knee and just below your kneecap. The discomfort usually isn't constant but tends to occur when you jump, run, squat or climb stairs. The quadriceps or patellar tendons may also rupture, either partially or completely. In that case, the pain is likely to be most intense when you try to extend your knee. If the tendon is completely ruptured, you won't be able to extend or straighten your knee at all.
  
• Meniscus Injuries. The meniscus is a C-shaped cartilage that curves within your knee joint. Meniscus injuries involve tears in the cartilage, which can occur in various places and configurations. Although you may not notice small tears, in most cases, you'll have pain and mild to moderate swelling that develops over 24 to 48 hours.  Meniscal injuries that cause locking of your knee should be surgically treated. Tears that don't cause locking, including those of a degenerative nature, can usually be managed without surgery.
  
• Bursitis. Some knee injuries cause inflammation in the bursae, the small sacs of fluid that cushion the outside of your knee joint so that tendons and ligaments glide smoothly over the joint. Bursitis can lead to warmth, swelling and redness over the inflamed area, aching or stiffness when you walk, and considerable pain when you kneel. Sometimes the bursa located over your kneecap bone (prepatellar bursa) can become infected, leading to fever, pain and swelling. When the bursa (pes anserine) on the lower inner side of your knee is affected, you're likely to have pain when you go up or down stairs.
  
• Loose Body. Sometimes injury or degeneration of bone or cartilage can cause a piece of bone or cartilage to break off and float in the joint space. This may not create any problems unless the loose body interferes with knee joint movement — the effect is something like a pencil caught in a door hinge — leading to pain and a locked joint.
  
• Dislocated Kneecap. This occurs when the triangular bone that covers the front of your knee (patella) slips out of place, usually to the outside of your knee. You'll be able to see the dislocation, and your kneecap is likely to move excessively from side to side. You're also likely to have intense pain and swelling in the affected area and difficulty walking or straightening your knee. Unfortunately, once you've had a dislocated kneecap, you're at increased risk of having it happen again. Although you may not experience as much swelling or discomfort with subsequent episodes, repeated dislocations can lead to chronic knee pain. But good rehabilitation, with a focus on strength training of the muscles that control your kneecap, can help prevent dislocation.
  
• Osgood-Schlatter Disease. Primarily affecting athletic teens and preteens, this overuse syndrome causes pain, swelling and tenderness at the bony prominence (tibial tuberosity) just below the kneecap. The pain, which can range from mild to debilitating, is usually worse with activity, especially running and jumping, and improves with rest. Osgood-Schlatter disease frequently affects just one knee, but sometimes develops in both knees. The discomfort can last from weeks to months and may continue to recur until your child stops growing.
  
• Hyperextended Knee. In this injury, your knee extends beyond its normally straightened position so that it bends back on itself. Sometimes the damage is relatively minor, with pain and swelling when you try to extend your knee. But a hyperextended knee may also lead to a partial or complete ligament tear, especially in your ACL.
  
• Septic Arthritis. Sometimes your knee joint can become infected, leading to swelling, pain and redness. Septic arthritis often occurs with a fever.

Chronic Knee Pain
Sometimes an injury can lead to ongoing (chronic) knee pain. Often, chronic pain results from a medical condition such as:

• Osteoarthritis. Sometimes called degenerative arthritis, this is the most common type of arthritis. It's a wear-and-tear condition that occurs when the cartilage in your knee deteriorates with use and age. Osteoarthritis usually develops gradually and tends to cause varying degrees of pain and swelling when you stand or walk and before a change in the weather. It also can lead to stiffness, especially in the morning and after you've been active, and to a loss of flexibility in your knee joints.
  
• Rheumatoid Arthritis. The most debilitating of the more than 100 types of arthritis, rheumatoid arthritis can affect almost any joint in your body, including your knees. In addition to pain and swelling, you're likely to have aching and stiffness, especially when you get up in the morning or after periods of inactivity; loss of motion in your knees and eventually deformity of the knee joints; and sometimes a low-grade fever and a general sense of not feeling well (malaise). Rheumatoid arthritis usually affects both knees at the same time. And although it's a chronic disease, it tends to vary in severity and may even come and go. Periods of increased disease activity — called flare-ups or flares — often alternate with periods of remission.
  
• Gout. With this type of arthritis, you're likely to experience redness, swelling and intense pain in your knee that comes on suddenly — often at night — and without warning. The pain typically lasts five to ten days and then stops. The discomfort subsides gradually over one to two weeks, leaving your knee joints apparently normal and pain-free.
  
• Chondromalacia of the Patella, or Patellofemoral Pain. This is a general term that refers to pain arising between your patella and the underlying thighbone (femur). It's common in young women, especially those who have a slight misalignment of the kneecap, in athletes, and in older adults, who usually develop the condition as a result of arthritis of the kneecap. Chondromalacia of the patella causes pain and tenderness in the front of your knee that's worse when you sit for long periods, when you get up from a chair and when you climb stairs. You may also notice a grating or grinding sensation when you extend your knee.

Physical therapy
Normally, the goal of physical therapy is to strengthen the muscles around your knee and help you regain knee stability. Depending on your injury, training is likely to focus on the muscles in the back of your thigh (hamstrings), the muscles on the front of your thigh (quadriceps), and your calf, hip and ankle. You can do some exercises at home. Others require the use of weight machines, exercise bicycles or treadmills, which may mean visits to an athletic club, fitness center or clinic.

Surgical options
There's no single best way to treat most knee injuries. Whether surgical treatment is right for you depends on many factors.

Other Options
In recent years, a number of nonsurgical treatments for knee pain that results from arthritis have been investigated or become available. Some are in the experimental stage, and others are used fairly routinely to control pain and inflammation. They include:

• Orthotics and Bracing. Arch supports, sometimes with wedges on the inner or outer aspect of the heel, can help to shift pressure away from the side of the knee most affected by osteoarthritis. A brace called an "unloader" brace also may be used to help ease the pressure on the most arthritic side of the knee.
  
• Glucosamine and Chondroitin. These substances, found naturally in cartilage, are also available as over-the-counter dietary supplements. Both may help relieve the pain of osteoarthritis of the knee. Unlike traditional anti-inflammatory drugs, which simply reduce inflammation, glucosamine appears to decrease the rate of cartilage destruction. A major, federally sponsored study of these substances is under way.
  
• Corticosteroid Injections. Injections of a corticosteroid drug into your knee joint may help reduce the symptoms of an arthritis flare and provide pain relief that lasts a few months. You usually must wait at least four months between injections. The injections aren't effective in all cases and cause some of the same side effects that oral steroid medications do, including an increased risk of infection, water retention and elevated blood sugar levels.

Sep 8, 2006
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