Knee Osteoarthritis, the most common type of osteoarthritis, is a chronic degeneration of the articular cartilage around a joint. Knee osteoarthritis most commonly affects people over 45 years of age but can occur at any time.
The bones of the knees joint (the backside of the kneecap, bottom of thighbone, and top of shinbone) are coated with smooth articular cartilage. When knee osteoarthritis develops, the cartilage undergoes gradual changes - losing elasticity, hardening, and cracking, becoming more easily damaged and eroded by use or injury.
The bones can't move smoothly over roughened cartilage, causing irritation to the bone. The end of the bones involved may thicken and bone spurs may form. Small bits of cartilage may break off and float around inside the knee. Over half of knee osteoarthritis sufferers also have mineral deposits in their cartilage. The joint fluid also changes in consistency, becoming thinner and less tacky, decreasing its lubricating and cushioning properties.
There are many different levels of severity of damage, from mild cases without symptoms or with mild symptoms to advanced cases where the cartilage is worn down to the point where bone rubs on bone, damaging the bones and causing severe knee pain.
Though osteoarthritis is considered to be non-inflammatory type of arthritis, minor inflammation is involved. The inflammation is not nearly as severe as the inflammation involved in inflammatory types of arthritis such as rheumatoid arthritis.
Knee osteoarthritis used to be considered a 'wear and tear' disease because it mainly affects middle-aged and elderly people and worsens over time. However, normal activity does not cause knee osteoarthritis, and the cause of cartilage deteriorating and wearing away is not known. Enzymes that damage the joint cartilage have been identified. Doxycycline, an antibiotic that has been shown to inhibit these enzymes, was shown to slow down cartilage deterioration in study led by Indiana University School of Medicine's arthritis and muscles diseases center. Cod liver oil has also been shown to inhibit these enzymes.
Many people reduce their activity because of knee pain or because they believe it will worsen knee osteoarthritis. As a result, the muscles that support the knee become weaker and more stress is placed on the knee joint.
Symptoms of Knee Osteoarthritis
The deterioration of cartilage is gradual and there may be no symptoms in the early stages of knee osteoarthritis. Symptoms of knee osteoarthritis are stiffness (especially morning knee stiffness), knee pain that is aggravated by going up or down stairs, limitation in range of motion, a crunching feeling in the knee, and weakness of knee. The knee may be swollen but not red and hot.
(Symptoms such as diffuse pain in knee joint and crunching sound in the knee can be caused by "runners knee", which is a common cause of knee pain in all age groups, including teens and young adults. See runners knee for more information)
Swelling of the knee may occur as a result of excess fluid accumulating within the knee joint. Damaged cartilage in the joint triggers inflammation of the joint lining (the synovium) and the excess production of joint fluid (synovial fluid).
An accumulation of excess fluid within a joint is called joint effusion. In the knee, joint effusion is sometimes referred to as water on the knee. Knee joint effusion sometimes results in a Baker's cyst.
In advanced cases, inflammation can also occur if bits of cartilage break off and float around inside the knee joint and cause irritation and inflammation of the soft tissue in the joint.
In advanced cases, there may be deformity of the joint. Cartilage has a limited ability to repair itself. The body compensates with the growth of extra bone, which results in visible enlargement of the joint.
Symptoms do not always correlate with the amount of damage to the joint. Symptoms can come and go for no apparent reason. This makes it difficult to assess whether or not a current treatment is working. Keeping the muscles that support the knee strong, keeping your weight down, and avoiding high impact activities can decrease the symptoms.
Diagnosing Knee Osteoarthritis
An x-ray may be helpful in diagnosing knee osteoarthritis. In a conventional x-ray the cartilage is invisible - how much cartilage has been lost is judged by the gap between the bones of the joint. A conventional x-ray can easily miss the early stages of knee osteoarthritis. And two radiologists may interpret the same x-rays differently. An MRI shows soft tissue (and bones) can also show the joint in motion
Diffraction Enhanced X-Ray Imaging (DEI) is a new type of x-ray that shows soft tissue as well as bone. DEI uses extremely low doses of radiation. The application of DEI to cartilage imaging is not yet in clinical use but efforts continue to make it commercially available.
Factors that Increase the Risk of Knee Osteoarthritis
- Genetic susceptibility
- Injury to the knee joint
- Lack of Exercise / Sedentary Lifestyle
- Muscle Weakness - weak quadriceps (muscles of the thigh that attach to the knee)
- Chronic Overuse / Overloading of knee joint (repetitive movements such as squatting/kneeling combined with heavy lifting or high impact activities such as running/jogging)
- Skewed feet
- Footwear (high heels)
Treatments for Knee Osteoarthritis
Exercise is beneficial for knee osteoarthritis: Strong leg muscles support the knee and absorb shock before it gets to the knee. Exercising the quad muscles increase circulation in the knee joint and has been shown to stimulate beneficial biochemical changes in the joint fluid of the knee, improving its lubricating properties. Exercise also improves the range of motion of the knee. However, in patients with knee osteoarthritis who have misaligned knees, over-strengthening of the quads can sometimes make matters worse. A doctor or physical therapist (physiotherapist) can determine whether or not your knees are properly aligned and which knee exercises would be most beneficial.
Heat and Cold
Applying heat to the knee joint reduces stiffness and pain by increasing blood flow. The heat is also a comforting distraction from the knee pain. DO NOT apply heat to an inflamed joint. Usually, inflammation is not present in the early stages of knee osteoarthritis.
Apply heat for 20 - 30 minutes at a time, waiting at least an hour between each application to prevent overheating of tissues. Dry or moist heat is beneficial but moist heat penetrates the tissues more quickly, and penetrates more deeply than dry.
For moist heat, you can use a towel soaked in warm water but it may cool off fairly quickly. An alternative is to place a moistened towel between your knee and a hot water bottle. There are also moist heating wraps available commercially.
*Do not use rubs and heat at the same time as a burn may occur.
Cold reduces knee inflammation and knee pain by constricting the blood vessels. Apply ice wrapped in cloth to an inflamed joint for 15 - 20 minutes every 3 or 4 hours. Do not ice for longer than 20 minutes at one time to avoid frostbite. Moist cold (Place a wet towel between the skin and an ice pack for moist cold) penetrates more deeply and quickly than dry cold.
*If you have circulation problems or nerve damage, do not use hot or cold therapies. (Unless a physician says it is safe for you)
Hydrotherapy is the use of water (liquid form or ice or in the form of steam) for therapeutic purposes. It includes exercising in a pool, soaking in a whirlpool, saunas, and hot and cold compresses. Soaking or doing exercises in warm water exercises are particularly beneficial for those who suffer from knee osteoarthritis.
Being overweight places extra stress on the knee, a weight-bearing joint. Even 10 pounds can make a big difference in the symptoms of knee osteoarthritis.
A recent study on acupuncture and knee osteoarthritis has shown that extended acupuncture treatment both reduces pain and increases function.
Though the reason it works is unclear, knee taping has been shown to significantly reduce knee pain in patients with knee osteoarthritis. There are different taping techniques that a physical therapist (physiotherapist) can teach a patient. Sometimes the skin can become irritated from the tape.
Used For Certain Cases of Knee Osteoarthritis: Unloader braces are designed to provide knee pain relief for those with knee osteoarthritis. They are very expensive but some health insurance plans cover them. Quite frequently, the cartilage is more worn out of one side of the knee joint, causing the thighbone to sit on an angle and the thighbone to rub against the shinbone on the worn out side. Unloader braces take off the load (pressure) on a knee joint by changing the angle of the knee joint. By changing the angle of the knee joint, a space between the thighbone and shinbone is created, relieving knee pain and increasing range of motion. An x-ray can determine if the space between the thighbone and shinbone is angled. A doctor or physical therapist (physiotherapist) can assess whether or not an unloader knee brace would be helpful in a particular case and recommend the appropriate knee brace.
Topical Creams for Knee Osteoarthritis:
Deep Heating Rubs, e.g. Creams applied directly to the knee joint give temporary pain relief by creating surface heat. (Do not apply heating rubs to inflamed joints) The heat is mainly a distraction from the knee pain.
Topical capsaicin: Capsaicin is an extract from red chili peppers. It can be purchased over the counter. Capsaicin reduces a substance in the nerve endings that transmit pain to the brain. It does not work immediately; the effects are accumulative. It can take 1 to 6 weeks of regular use to obtain the full effect. The benefits seem to add to the benefits of pain medications and/or anti-inflammatory medications.
Tens therapy involves stimulating nerve endings with low voltage electric impulses through electrodes attached to the body at the site of the pain. It relieves pain in some patients.
Joint fluid contains hyaluronic acid (hyaluronate), which makes the fluid thick and sticky. In osteoarthritis, the production of hyaluronic acid decreases and its concentration in the joint fluid is reduced. This results in a thinner fluid, with reduced ability to lubricate the joint and to absorb shock.
Viscosupplementation Treatment consists of a series of 3 injections over 3 weeks. A fluid (hyaluronates) similar to normal joint fluid is injected into your knee joint to lubricate and cushion it. (In cases of knee osteoarthritis, the normal gel-like joint fluid - synovial fluid - becomes thinner) The knee pain relief usually lasts for 6 - 9 months. If the symptoms recur, the injections can be repeated. The success rate is very high in milder cases, and even in the most severe cases the success rate is over half.
Hyalgan is the first FDA-approved hyaluronan therapy (viscosupplementation) in the US for Osteoarthritis of the knee. Other FDA-approved hyaluronates for hyaluronan therapy includes Synvisc, Supartz, and Orthovisc.
Arthoscopic surgery: Non-invasive surgery, a camera attached to video monitor is inserted through small incision. This is minor surgery, usually performed on an outpatient basis. Rough damaged cartilage can be shaved; bone spurs can be removed, loose bits of cartilage cleaned out.
Knee Replacement Surgery:
Also called knee arthroplasty, this is major surgery and is a last resort option for extreme cases of knee osteoarthritis, when all else fails to relieve pain. A knee replacement is not perfect - it has a limited life span of 10 - 20 years. This procedure makes it possible to carry on everyday activities without pain and to do low impact aerobics, however, overuse will accelerate wearing out the parts.
Unfortunately, this is NOT an option for those with knee osteoarthritis. This can only be done only for small defects in the articular cartilage, not for the more common diffuse damage seen in knee osteoarthritis. A cartilage transplant is done by taking small pieces of cartilage from an area of the knee where there is minimum weight bearing, growing cartilage outside the body and transplanting in back into the damaged part can repair minor defects.
Medications: See Medications page.
Glucosamine AND Chondroitin and Other Supplements:
Studies are ongoing to determine whether or not glucosamine and chondroitin can reduce or halt the progression of knee osteoarthritis.
Knee osteoarthritis is a chronic, progressive condition. Combining several therapies may be required to adequately manage the symptoms of knee osteoarthritis - exercise, Medications, knee taping, unloader knee braces in some cases, heat and cold, topical creams, and complementary supplements such as cod liver oil, glucosamine, chondroitin. Since the symptoms can come and go it may take a while to know if treatment is effective. If conservative treatments aren't enough, corticosteroids can be injected into the knee joint, viscosupplementation injections, and when all else fails, knee replacement surgery.