What You Need to Know About Osteoarthritis

What is osteoarthritis?

Arthritis means joint inflammation, which causes joint pain and swelling. There are many types of arthritis and osteoarthritis is the most common type. Also known as degenerative joint disease, or age-related arthritis, osteoarthritis is more likely to develop in people as they age. Inflammation and injury to the joint result in breakdown and erosion of cartilage tissues and changes in the bone of joints that can result in pain, swelling and deformity. The changes in osteoarthritis usually occur slowly over many years, though there are occasional exceptions. There are two main types of osteoarthritis, a primary more generalized form affecting the fingers, thumbs, spine, hips and knees, and secondary osteoarthritis that occurs after injury or inflammation in a joint.

Figure 1: Normal joint

What is cartilage?

Cartilage is a firm, rubbery material covering the ends of bones in normal joints. It is primarily composed of water and proteins (see Figure 1) whose primary function is to reduce friction in the joints and serve as a “shock absorber.” The shock-absorbing quality of normal cartilage comes from its ability to change shape when compressed, as a result of its high water content. Although cartilage may undergo some repair when damaged, the body does not regenerate new cartilage after injury.

Cartilage is composed of two main elements: a gel-like substance called matrix composed primarily of water and two types of proteins – collagen and proteoglycans - and cells contained within the matrix known as chondrocytes.

• Collagen: is a structural protein found in many tissues such as skin, tendons and bone, and is a key structural component of cartilage. Collagen provides cartilage with its strength, and creates a framework for the other components of cartilage.
• Proteoglycans are complex molecules composed of protein and sugar combinations that are interwoven in the matrix of cartilage. Their function is to trap large amounts of water in cartilage, which allow it to change shape when compressed and thus act as shock absorber.
• Water: Healthy cartilage is primarily composed of water, forming a ‘gel-like’ matrix with the other components outlined, allowing it to function as the “shock absorber” for the joint. In diseases like osteoarthritis cartilage loses a lot of its water content diminishing its capacity to protect the joint.
• Chondrocytes are highly complex multifunctional cartilage cells. They produce collagen and proteoglycans, and manufacture enzymes involved in the maintenance of healthy cartilage. As cartilage forms, these cells migrate through the different layers of cartilage, changing as they do so by mechanisms not fully understood.

What causes osteoarthritis?

Osteoarthritis has two main causes as mentioned earlier: a primary generalized form which appears hereditary and a secondary form which happens when a joint that has previously been damaged by trauma or inflammation. Primary generalized osteoarthritis affects women more than men, often occurring shortly after menopause. Most people have other family members affected by the same problem, and usually have swelling and or pain of the finger joints, base of thumbs and knees or hips. Secondary osteoarthritis may occur in a joint that was previously injured from trauma, or after the joint has been damaged by some other form of arthritis such as infection or rheumatoid arthritis.

Although the exact mechanisms of cartilage loss and bone changes are unknown, great advancements have been made in recent years. It is likely that complex signaling processes during joint inflammation, and defective repair mechanisms in response to injury, gradually erode cartilage within the joints. Other changes cause the joint to lose mobility and function resulting in joint pain with activity.

Who is affected by osteoarthritis?

Although the majority of older individuals (>60 years) have evidence of osteoarthritis by x-ray, most have no symptoms. Current estimates suggest that over 20 million U.S. adults have symptomatic osteoarthritis. Women have a three-fold higher risk of developing primary generalized osteoarthritis than men. Because age is a risk factor, people are more likely to develop this form of arthritis as they get older.

Are there other risk factors for osteoarthritis?

In addition to hereditary factors (genes) and other forms of arthritis, several other risk factors increase the risk for developing osteoarthritis including other hereditary disorders, obesity, and injuries to or around the joint.

• Hereditary: Individuals born with other diseases are more likely to develop osteoarthritis. Examples include conditions associated with increased joint laxity (being “double-jointed”) some dysplasias (abnormal growth of bone and cartilage) and Paget’s disease of bone (a type of inflammation in bone that occurs in older people).
• Obesity is a risk factor for osteoarthritis of the lower extremity and spine. It is not only a risk factor, but being overweight may accelerate the rate of development of osteoarthritis. Thus maintenance of ideal body weight or losing excess weight is important for those at risk.
• Injuries contribute to the development of osteoarthritis such as occurs in many athletes. An injury that results in abnormal stress on a joint is another important risk factor for osteoarthritis. Overuse injuries are more controversial as many people who have similar lifestyles do not develop osteoarthritis. However repetitive trauma – which may result from overuse – does increase that risk.
• Other Conditions predisposing to the development of osteoarthritis include peripheral neuropathies and neuromuscular disorders that put abnormal stress on the joint.

How Would I know if I have Osteoarthritis?

Unlike other types of arthritis, the pain from osteoarthritis usually develops gradually over many months or years. Often it increases with activities that put a lot of stress on the joint such as running or prolonged walking. Morning stiffness is not a prominent symptom, usually lasting less than 20-30 minutes. Pain and joint swelling tend to increase slowly over time. Sometimes, especially in more advanced disease, a sensation of crunching or grinding may be noticed in affected joints.

Your doctor or health care provider can usually tell if you have osteoarthritis from listening to your symptoms and examining your joints. Occasionally x-rays are needed to make sure there is no other reason for the pain. Magnetic Resonance Imaging (MRI test) is generally not needed except in unusual circumstances or if a cartilage tear is suspected. There are no blood tests that diagnose osteoarthritis. Sometimes if a joint is particularly swollen then your doctor may need to drain fluid from that joint. Tests can be performed on the fluid to look for clues for other types of arthritis.

Osteoarthritis does not cause fevers, weight loss or very hot and red joints. These features suggest there is some other condition or type of arthritis going on.

Treatment of Osteoarthritis?

Osteoarthritis is usually treated by taking medications to relieve pain, exercises, and other therapies. This is dealt with in more detail in the treatment section .