Osteoarthritis

Osteoarthritis
Specialty	Family medicine, orthopedic surgery, rheumatology

Osteoarthritis (OA) also known as degenerative arthritis or degenerative joint disease or osteoarthrosis, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion. A variety of causes—hereditary, developmental, metabolic, and mechanical deficits—may initiate processes leading to loss of cartilage. When bone surfaces become less well protected by cartilage, bone may be exposed and damaged. As a result of decreased movement secondary to pain, regional muscles may atrophy, and ligaments may become more lax.

Treatment generally involves a combination of exercise, lifestyle modification, and analgesics. If pain becomes debilitating, joint replacement surgery may be used to improve the quality of life. OA is the most common form of arthritis, and the leading cause of chronic disability in the United States. It affects about 8 million people in the United Kingdom and nearly 27 million people in the United States.

Signs and symptoms

Bouchard's nodes and Heberden's nodes may form in osteoarthritis

The main symptom is pain, causing loss of ability and often stiffness. "Pain" is generally described as a sharp ache, or a burning sensation in the associate 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 and cold weather increases the pain in many patients.

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 better with gentle use but worse with excessive or prolonged use, 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. Some people notice these physical changes before they experience any pain.

OA is the most common cause of joint effusion, sometimes called water on the knee in lay terms, an accumulation of excess fluid in or around the knee joint.

Causes

Some investigators believe that mechanical stress on joints underlies all OA, with many and varied sources of mechanical stress, including misalignments of bones caused by congenital or pathogenic causes; mechanical injury; overweight; loss of strength in muscles supporting joints; and impairment of peripheral nerves, leading to sudden or uncoordinated movements that overstress joints. However exercise, including running in the absence of injury, has not been found to increase one's risk of developing OA. Nor has cracking one's knuckles been found to play a role.

Primary

Primary osteoarthritis of the left knee. Note the osteophytes, narrowing of the joint space (arrow), and increased subchondral bone density (arrow).

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[ as a result of a reduced proteoglycan content, thus causing the cartilage to be less resilient. The water content of healthy cartilage is finely balanced by compressive force driving water out & swelling pressure drawing water in. Collagen fibres exert the compressive force, whereas the Gibbs-Donnan effect & cartilage proteoglycans create osmotic pressure which tends to draw water in. However during onset of OA there is an increase in cartilage water content. This increase occurs because whilst there is an overall loss of proteoglycans, it is outweighed by a loss of collagen. 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 what 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.

A number of studies have shown that there is a greater prevalence of the disease among siblings and especially identical twins, indicating a hereditary basis. Although a single factor is not generally sufficient to cause the disease, about half of the variation in susceptibility has been assigned to genetic factors.

The development of OA is correlated with a history of previous joint injury and with obesity, especially with respect to knees. Since the correlation with obesity has been observed not only for knees but also for non-weight bearing joints and the loss of body fat is more closely related to symptom relief than the loss of body weight, it has been suggested that there may be a metabolic link to body fat as opposed to just mechanical loading.

Changes in sex hormone levels may play a role in the development of OA as it is more prevalent among post-menopausal women than among men of the same age. A study of mice found natural female hormones to be protective while injections of the male hormone Dihydrotestosterone reduced protection.

Secondary

This type of OA is caused by other factors but the resulting pathology is the same as for primary OA:

• Alkaptonuria
• Congenital disorders of joints
• Diabetes
• Ehlers-Danlos Syndrome
• Hemochromatosis and Wilson's disease
• 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 or ligaments (such as the ACL), as a result of an accident or orthopedic operations.
• Ligamentous deterioration or instability may be a factor.
• Marfan syndrome
• Obesity
• Septic arthritis (infection of a joint)

Diagnosis

Diagnosis is made with reasonable certainty based on history and clinical examination. X-rays may confirm the diagnosis. The typical changes seen on X-ray include: joint space narrowing, subchondral sclerosis (increased bone formation around the joint), subchondral cyst formation, and osteophytes. Plain films may not correlate with the findings on physical examination or with the degree of pain. Usually other imaging techniques are not necessary to clinically diagnose OA.

In 1990, the American College of Rheumatology, using data from a multi-center study, developed a set of criteria for the diagnosis of hand OA based on hard tissue enlargement and swelling of certain joints. These criteria were found to be 92% sensitive and 98% specific for hand OA versus other entities such as rheumatoid arthritis and spondyloarthropathies.

Related pathologies whose names may be confused with OA include pseudo-arthrosis. This is derived from the Greek words pseudo, meaning "false", and arthrosis, meaning "joint." Radiographic diagnosis results in diagnosis of a fracture within a joint, which is not to be confused with OA which is a degenerative pathology affecting a high incidence of distal phalangeal joints of female patients. A polished ivory-like appearance may also develop on the bones of the affected joints, reflecting a change called eburnation.

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  Damaged cartilage in gross pathological specimen from sows. (a) cartilage erosion (b)cartilage ulceration (c)cartilage repair (d)osteophyte (bone spur) formation.
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  Histopathology of osteoarthrosis of a knee joint in an elderly female.
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  Severe osteoarthritis and osteopenia of the carpal joint and 1st carpometacarpel joint.

Classification

OA can be classified into either primary or secondary depending on whether or not there is an identifiable underlying cause.

Both primary generalized nodal OA and erosive OA (EOA. also called inflammatory OA) are sub-sets of primary OA. EOA is a much less common, and more aggressive inflammatory form of OA which often affects the distal interphalangeal joints and has characteristic changes on x-ray.

Management

Lifestyle modification (such as weight loss and exercise) and analgesics are the mainstay of treatment. Acetaminophen / paracetamol is used first line and NSAIDs are only recommended as add on therapy if pain relief is not sufficient. This is due to the relative greater safety of acetaminophen.

Lifestyle modification

For overweight people, weight loss may be an important factor. Patient education has been shown to be helpful in the self-management of arthritis. It decreases pain, improves function, reduces stiffness and fatigue, and reduces medical usage. A meta-analysis has shown patient education can provide on average 20% more pain relief when compared to NSAIDs alone in patients with hip OA.

Physical measures

For most people with OA, graded exercise should be the mainstay of their self-management. Moderate exercise leads to improved functioning and decreased pain in people with OA of the knee. While there is some evidence for certain physical therapies evidence for the combined program is limited.

There is sufficient evidence to indicate that physical interventions can reduce pain and improve function. There is some evidence that manual therapy is more effective than exercise for the treatment of hip OA, however this evidence could be considered to be inconclusive. Functional, gait, and balance training has been recommended to address impairments of proprioception, balance, and strength in individuals with lower extremity arthritis as these can contribute to higher falls in older individuals.

Orthotics

The use of orthoses (commonly referred to as splints, braces or insoles as applicable) can reduce the symptoms of OA at various joints. In the lower limb, orthoses are used for the foot and ankle and knee. In the upper limb, splinting of the base of the thumb leads to improvements after one year.

Medication

Analgesics

Paracetamol (INN; acetaminophen is the USAN) is the first line treatment for OA. For mild to moderate symptoms effectiveness is similar to non-steroidal anti-inflammatory drugs (NSAIDs), though for more severe symptoms NSAIDs may be more effective. NSAIDs such as ibuprofen while more effective in severe cases are associated with greater side effects such as gastrointestinal bleeding. Another class of NSAIDs, COX-2 selective inhibitors (such as celecoxib) are equally effective to NSAIDs with lower rates of adverse gastrointestinal effects but higher rates of cardiovascular disease such as myocardial infarction. They are also much more expensive. There are several NSAIDs available for topical use including diclofenac. They have fewer systemic side-effects and at least some therapeutic effect. While opioid analgesics such as morphine and fentanyl improve pain, this benefit is outweighed by frequent adverse events and thus they should not routinely be used.

Other

Oral steroids are not recommended in the treatment of OA because of their modest benefit and high rate of adverse effects. Injection of glucocorticoids (such as hydrocortisone) leads to short term pain relief that may last between a few weeks and a few months. Topical capsaicin and joint injections of hyaluronic acid have not been found to lead to significant improvement. Hyaluronic acid injects have been associated with significant harm.

Surgery

If disability is significant and the above management is ineffective, joint replacement surgery or resurfacing may be recommended. Evidence supports joint replacement for both knees and hips. For the knee it improves both pain and functioning. Arthroscopic surgical intervention for OA of the knee however has been found to be no better than placebo at relieving symptoms.

Alternative medicine

The following show promise as treatments for OA avocado/soybean unsaponifiables, boswellic acid, cat's claw, curcumin, chondroitin, Devil's claw, glucosamine sulfate , S-Adenosyl methionine and TENS.

Acupuncture

A Cochrane review found that while acupuncture leads to a statistically significant improvement in pain relief, this improvement is small and may be of questionable clinical significance. Waiting list-controlled trials for peripheral joint OA do show clinically relevant benefits, but these may be due to placebo effects. Acupuncture does not seem to produce long-term benefits.

Glucosamine

Controversy surrounding glucosamine may be due to including the ineffective hydrochloride and the effective sulfate preperations of glucosamine as well as different treatment protocols and preperations.. A 2010 meta-analysis has found that it is no better than placebo. Glucosamine sulfate is an effective treatment The Osteoarthritis Research Society International (OARSI) recommends that glucosamine be discontinued if no effect is observed after six months.

Epidemiology

Disability-adjusted life year for OA per 100,000 inhabitants in 2004. Template:Multicol

  no data

  ≤ 200

  200–220

  220–240

  240–260

  260–280

  280–300

Template:Multicol-break

  300–320

  320–340

  340–360

  360–380

  380–400

  ≥ 400

Template:Multicol-end

OA affects nearly 27 million people in the United States, accounting for 25% of visits to primary care physicians, and half of all NSAID prescriptions. It is estimated that 80% of the population have radiographic evidence of OA by age 65, although only 60% of those will have symptoms. In the United States, hospitalizations for OA increased from 322,000 in 1993 to 735,000 in 2006.

Globally OA causes moderate to severe disability in 43.4 million people as of 2004.

Etymology

OA is derived from the Greek word part osteo-, meaning "of the bone", combined with arthritis: arthr-, meaning "joint", and -itis, the meaning of which has come to be associated with inflammation. The -itis of OA could be considered misleading as inflammation is not a conspicuous feature. Some clinicians refer to this condition as osteoarthosis to signify the lack of inflammatory response.

History

Evidence for OA found in the fossil record is studied by paleopathologists, specialists in ancient disease and injury. OA has been reported in fossils of the large carnivorous dinosaur Allosaurus fragilis.

Research

There are ongoing efforts to determine if there are agents that modify outcomes in OA. Sprifermin is one candidate drug. There is also tentative evidence that strontium ranelate may decrease degeneration in OA and improve outcomes.

External links

• American College of Rheumatology Factsheet on OA
• Osteoarthritis The Arthritis Foundation