Osteoarthritis (OA, also known as degenerative arthritis, degenerative joint disease), is a condition in which low-grade inflammation results in pain in the joints, caused by abnormal wearing of the cartilage that covers and acts as a cushion inside joints and destruction or decrease of synovial fluid that lubricates those joints. As the bone surfaces become less well protected by cartilage,  pain is experienced upon weight bearing, including walking and standing. Due to decreased movement because of the pain, regional muscles may atrophy, and  ligaments may become more lax.

"Osteoarthritis" is derived from the Greek word "osteo", meaning "of the bone", "arthro", meaning "joint", and "itis", meaning inflammation, although many sufferers have little or no inflammation.

A common misconception is that OA is due solely to wear and tear, due to the fact that OA typically is not present in younger people. However, while age is correlated with OA incidence, this merely illustrates that OA is a process that takes time to develop. There is usually an underlying cause for OA, in which case it is described as secondary OA. If no underlying cause can be identified it is described as primary OA. "Degenerative arthritis", often used as a synonym for OA, but the latter involves both degenerative and regenerative changes.

OA affects nearly 21 million people in the United States, accounting for 25% of visits to primary care physicians, and half of all NSAID (Non-Steroidal Anti-Inflammatory Drugs) prescriptions.

More than 10 million Americans havie a total joint replacement each year.

It is estimated that 80% of the population will have radiographic evidence of OA by age 65, although only 60% of those will be symptomatic.

OA commonly affects the hands, feet, spine, and the large weight-bearing joints, such as the hips and knees, although in theory, any joint in the body can be affected. As OA progresses, the affected joints appear larger, are stiff and painful, and usually feel worse, the more they are used throughout the day, thus distinguishing it from rheumatoid arthritis.

In smaller joints, such as at the fingers, hard bony enlargements, called Heberden's nodes (on the distal interphalangeal joints) and/or Bouchard's nodes (on the proximal interphalangeal joints), may form, and though they are not necessarily painful, they do limit the movement of the fingers significantly. OA at the toes leads to the formation of bunions, rendering them red or swollen.

The main symptom is chronic pain, causing loss of mobility and often stiffness. "Pain" is generally described as a sharp ache, or a burning sensation in the associated muscles and tendons.

OA can cause a crackling noise (called "crepitus") when the affected joint is moved or touched, and patients may experience muscle spasm and contractions in the tendons. Occasionally, the joints may also be filled with fluid. Humid weather increases the pain in many patients.

OA  commonly arises from trauma. However there is data suggesting that there may also be a genetic factor. 

Factors Associated with Progression of OA:

• Knees: High body mass index, varus or valgus knee deformity.
• Hips: Night pain, presence of femoral osteophytes, and subchondral sclerosis in females.
• Hands: Older age.

Primary OA

Primary  OA is a chronic degenerative disorder related to but not caused by aging, as there are people well into their nineties who have no clinical or functional signs of the disease.

As a person ages, the water content of the cartilage decreases due to a reduced proteoglycan content, thus causing the cartilage to be less resilient. Without the protective effects of the proteoglycans, the collagen fibers of the cartilage can become susceptible to degradation and thus exacerbate the degeneration. Inflammation of the surrounding joint capsule can also occur, though often mild (compared to that which occurs in rheumatoid arthritis). This can happen as breakdown products from the cartilage are released into the synovial space, and the cells lining the joint attempt to remove them. New bone outgrowths, called "spurs" or osteophytes, can form on the margins of the joints, possibly in an attempt to improve the congruence of the articular cartilage surfaces. These bone changes, together with the inflammation, can be both painful and debilitating.

Secondary OA

• Congenital disorders, such as:
  • Congenital hip luxation.People with abnormally-formed joints (e.g. hip dysplasia (human)) are more vulnerable to OA, as added stress is specifically placed on the joints whenever they move. [Recent studies have shown that double-jointedness may actually protect the fingers and hand from osteoarthritis.]
• Cracking joints—the evidence is weak at best that this has any connection to arthritis.
• Diabetes.
• Inflammatory diseases (such as Perthes' disease), (Lyme disease), and all chronic forms of arthritis (e.g. costochondritis, gout, and rheumatoid arthritis). In gout, uric acid crystals cause the cartilage to degenerate at a faster pace.
• Injury to joints, as a result of an accident.
• A joint infection, e.g. from an injury.
• Hormonal disorders.
• Ligamentous deterioration or instability may be a factor.
• Obesity. Obesity puts added weight on the joints, especially the knees.
• Sports injuries, or similar injuries from exercise or work. Certain sports, such as running or football, put undue pressure on the knee joints. Injuries resulting in broken ligaments can lead to instability of the joint and over time to wear on the cartilage and eventually osteoarthritis.
• Pregnancy
• Alkaptonuria
• Hemochromatosis and Wilson's disease

Diagnosis is normally done through x-rays. This is possible because loss of cartilage, subchondral ("below cartilage") sclerosis, subchondral cysts, narrowing of the joint space between the articulating bones, and bone spur formation (osteophytes) show up clearly on x-rays. There are no methods available to detect OA in its early and potentially treatable stages.

Treatment

There has been no cure for OA, as cartilage has not been induced to regenerate. However, if OA is caused by cartilage damage (for example as a result of an injury) Autologous Chondrocyte Implantation may be a possible treatment.^] Clinical trials employing tissue-engineering methods have demonstrated regeneration of cartilage in damaged knees, including those that had progressed to osteoarthritis.In January 2007, Johns Hopkins University was offering to license a technology of this kind,  listing several clinical competitors in its market analysis.

Generally speaking, the process of osteoarthritis is irreversible, and typical treatment consists of medication or other interventions that can reduce the pain of OA and thereby improve the function of the joint.

Standard conservative lifestyle treatment options may include:

• Weight control
• Appropriate rest
• Regular exercise, if possible, in the form of walking or swimming, is encouraged. Applying local heat before, and cold packs after exercise, can help relieve pain and inflammation, as can relaxation techniques.

• Heat — often moist heat — eases inflammation and swelling, and may improve circulation, which has a healing effect on the local area.
• In OA of the knees, knee braces, a cane, or a walker can be helpful for walking and support.

• (Non-steroidal anti-inflammatory drugs (NSAIDs). These are drugs with analgesic, antipyretic and anti-inflammatory effects - they reduce pain, fever and inflammation.  NSAIDs are non steroidal, are non-narcotic. NSAIDs are sometimes also referred to as non-steroidal anti-inflammatory agents/analgesics (NSAIAs) or non-steroidal anti-inflammatory medicinesNSAIMs). The most prominent members of this group of drugs are aspirin, ibuprofen, and naproxen partly because they are available over-the-counter in many areas. 
• Local injections of glucocorticoid or hyaluronan, and
• In severe cases, with joint replacement surgery.
  

Other nutritional changes shown to aid in the treatment of OA include:

• Decreasing saturated fat and using a low energy diet to decrease body fat. 
• A low fat vegetarian diet can reduce arthritis symptoms.
• A macrobiotic diet has been known to reduce symptoms as well.

• Glucosamine. Supplemental glucosamine may improve symptoms of OA and delay its progression. The jury is still out as there are studies that show the benefit, while other studies conclude that glucosamine hydrochloride is not effective and that the effect of glucosamine sulfate is uncertain.
• Chondroitin sulfate . Along with glucosamine, chondroitin sulfate has become a widely used dietary supplement for treatment of osteoarthritis. The Osteoarthritis Research Society International is in support of the use of chondroitin sulfate for OA, however there have been studies which have found no benefit from chondroitin.

• Antioxidants, including vitamins C and E in both foods and supplements, provide pain relief from OA.
• Boswellia, an herbal supplement known in Ayurvedic medicine. It is widely available in health food stores and online.
• Ginger (rhizome) extract - has improved knee symptoms moderately.
• Hydrolyzed collagen (hydrolysate) (a gelatin product) may also prove beneficial in the relief of OA symptoms, as substantiated in a German study by Beuker F. et al. and Seeligmuller et al. In their 6-month placebo-controlled study of 100 elderly patients, the verum group showed significant improvement in joint mobility.
• Omega-3 fatty acid,a vitamin supplement comprised of important oils derived from fish.
• Selenium deficiency has been correlated with a higher risk and severity of OA.
• Vitamins B9 (folate) and B12 (cobalamin) taken in large doses significantly reduced OA hand pain, presumably by reducing systemic inflammation.
• Vitamin D deficiency has been reported in patients with OA, and supplementation with Vitamin D3 is recommended for pain relief.

If the above management is ineffective, joint replacement surgery may be required. Individuals with very painful OA joints may require surgery such as fragment removal, repositioning bones, or fusing bone to increase stability and reduce pain.

A meta-analysis of randomized controlled trials of acupuncture for knee osteoarthritis concluded "clinically relevant benefits, some of which may be due to placebo or expectation effects".

Low level laser therapy is a light wave based treatment that may reduce pain. The treatment is painless, inexpensive and without risks or side effects. Unfortunately, it may not actually have any real benefits.

Prolotherapy s the injection of an irritant substance (such as dextrose) to create an acute inflammatory reaction. It is claimed to strengthen and heal damaged tissues including ligaments, tendons and cartilage as part of this reaction. The injection is painful (like corticosteroids or hyaluronic acid) and may cause an increase in pain for a few days afterwards. The only other significant risk is the rare possibility of infection.

A radioactive isotope (a beta-ray emitter with a brief half-life) is injected into the joint to soften the tissue. Due to the involvement of radioactive material, this is an elaborate and costly procedure, but it has a success rate of around 80%.

The most common course of OA is an intermittent, progressive worsening of symptoms over time, although in some patients the disease stabilizes. Prognosis also varies depending on which joint is involved.