What is osteoarthritis?

Osteoarthritis^[1] (OA) is the most common form of arthritis (the inflammation of one or more of the body’s joints). It occurs when tissues in the joints break down, either over time due to natural wear and tear or as the result of an injury. Any joint in the body can be affected by osteoarthritis, but the most commonly affected areas^[2] are weight-bearing or frequently used joints, such as those in the hands, knees, hips, and spine.Normal, healthy joints are surrounded by pieces of tissue called cartilage. This cartilage protects the surfaces of the bones and ensures that they can move smoothly against one another as the joints move. Over time, the cartilage can become worn down and damaged, causing friction and grinding between the bones. This is known as osteoarthritis. In some cases, the body may attempt to repair the effects of worn cartilage to allow joints to function normally and without pain. However, these repairs may cause slight changes to the structure of the joints themselves. Furthermore, this repair mechanism is not always thorough enough to eliminate symptoms like pain, swelling, and limited range of motion.

How common is osteoarthritis?

OA is the most common joint disorder. It affects approximately 32.5 million adults^[3] in the United States. Before age 45, OA is more common in men^[4], but after age 45, it is more common in women. Osteoarthritis is seen more frequently in people over the age of 50^[5] than in children, adolescents, and younger adults.

Osteoarthritis vs. rheumatoid arthritis

There are more than 100 forms of arthritis. The two most common are osteoarthritis and rheumatoid arthritis (RA). The causes and risk factors for OA and RA differ. Research suggests that while there is a possible genetic component to the origin of OA, it is primarily caused by joint strain, repetitive joint stress (wear over time), and improperly healed joint injuries. Osteoarthritis is a degenerative condition, meaning it worsens over time. Rheumatoid arthritis^[6], alternatively, is a systemic condition (meaning it affects the entire body, as opposed to individual joints). It stems from an autoimmune disorder that involves the production of antibodies that attack healthy joint tissue. This causes the body’s joints to become inflamed, even without injury or wear and tear. The cause of this antibody production is unknown; however, risk factors for RA include possible genetic, environmental, and hormonal components. Your risk of developing RA also increases if you are a smoker or are obese. While some of the symptoms of RA and OA are similar (joint pain, stiffness, swelling), the rate at which the symptoms develop and the severity of the symptoms differ. Osteoarthritis symptoms develop slowly and generally continue to worsen over time, while the symptoms of rheumatoid arthritis can arise quickly and worsen within weeks to months. Because RA is a systemic condition, its joint symptoms are seen symmetrically on both the left and right sides of the body. OA, alternatively, usually only affects one or a few joints in particular. Additionally, RA can cause symptoms like fever and fatigue, while the symptoms of OA are localized to just the affected joints. One characteristic symptom of OA is stiffness in the morning or after sitting for prolonged periods, which usually resolves within 30 to 60 minutes. While people with RA also tend to have stiffness after sleeping or sitting, the stiffness tends to remain for a longer period of time than it does in people with OA. The methods used to diagnose OA and RA are similar. However, in the case of suspected RA, certain blood tests may be used to check for the presence of particular antibodies. The inflammatory symptoms of RA and OA are treated similarly, typically through the use of nonsteroidal anti-inflammatory medications (NSAIDs). People with RA may also be prescribed immune medications to prevent more antibodies from forming. Many healthcare providers will also recommend physical therapy, weight management, and healthy lifestyle decisions for people with both RA and OA.

Osteoarthritis causes

Osteoarthritis is also known as degenerative joint disease^[7] (DJD). It is categorized as a heterogeneous disease, meaning its causes are multifactorial. Some causes of osteoarthritis are modifiable (weight, stress on the joints, overuse), while others are non-modifiable (age, genetics, sex, race). Osteoarthritis was previously thought to be a condition^[8] that developed solely from repeated “wear and tear” of joints over time. However, more recent research suggests that OA is instead a disease of the joint, wherein cartilage between the bones breaks down more quickly or more severely than during the normal aging process. Certain inherited disorders, such as Ehlers-Danlos syndrome^[9] (a disease that affects the body’s connective tissues and causes hypermobility and joint laxity), may be correlated with a person’s likelihood of developing osteoarthritis. Over time, this disease can affect the cartilage around the joints, contributing to the symptoms of osteoarthritis. OA can also be caused in part by metabolic, hormonal, or inflammatory factors, such as diabetes, elevated cholesterol, and decreased estrogen levels in post-menopausal women. Diabetes and elevated cholesterol are known to result in inflammation^[10] in the body, which can contribute to one’s risk of developing osteoarthritis. Diabetes, which is often associated with elevated blood sugar, can also increase free radicals, resulting in oxidative stress. On a cellular level, oxidative stress can lead to excess stress on the cartilage in the body. This excess stress can ultimately contribute to joint damage as well. Hyperlipidemia, or increased cholesterol levels, can also create an inflammatory response in the body. Lipid oxidation may also cause lipid deposits to form in cartilaginous tissue. These deposits may affect the way blood flows around joints and bones, thus increasing the risk of developing osteoarthritis.

Risk factors for osteoarthritis

Some modifiable (changeable) and non-modifiable factors⁴ may increase your risk of developing osteoarthritis, including:

• Age: Your risk of developing OA increases as you get older due to your muscles, bones, and joints aging and wearing down.
• Joint injury: Joint rips or tears can cause OA to develop even years after an injury has occurred.
• Overuse: Repetitive use of a joint through sports or occupational (job) functions can contribute to developing OA.
• Obesity: Carrying excess weight can put undue stress on joints. Additionally, fat cells (adipocytes) can promote inflammatory processes, which contribute to the progression of OA.
• Weak muscles: Poor muscle support can cause joints to move out of their normal positions, causing joint stress over time.
• Genetics: If you have a close family member with OA, you are at increased risk of developing the condition yourself.
• Race: African-Americans are more likely^[11] to develop knee or hip OA than people of other ethnicities.
• Sex: Women are more likely to have OA than men after age 45. Conversely, women are less likely than men to have OA before age 45.

Osteoarthritis symptoms

The main symptoms^[12] of OA are joint pain, stiffness, and restricted movement. Some people also experience muscle weakness, poor balance, and co-occurring diseases, such as fibromyalgia. Common signs and symptoms^[13] of OA include:

• Pain: Joints may be sore or achy during or after normal movement.
• Stiffness: One of the most common symptoms of OA; may be most noticeable when moving for the first time after sitting for a prolonged period or when getting up after sleeping.
• Tenderness: You may feel tenderness in your joints when you apply pressure on or near the affected area(s).
• Grating sensation: You may experience grating around the joint area, as well as popping or cracking when using the joint. This occurs when there is insufficient cartilage to cushion the bones and prevent them from rubbing together.
• Limited range of motion: You may find yourself unable to move your joints/muscles to the same extent you once were able to.
• Joint deformity: A symptom of advanced (late-stage) OA is joint deformity, which presents as curling or folding of fingers or toes.
• Swelling: Inflammation around the joints may cause them to become swollen.
• Bone spurs: These hard, lump-like bony structures can form around affected joints.

While these symptoms are common to nearly all affected areas, there are some location-specific symptoms^[14] seen in osteoarthritis as well:

• Hands:: Women are more likely to develop OA in their hands. For most women, the condition begins to affect them after menopause. The most common symptom of OA in the hands is the presence of bony protrusions called Heberden’s nodes or Bouchard’s nodes. These occur on the joints closest to the tip of the finger and on the joints in the middle of the finger, respectively. When osteoarthritis in the hands becomes more severe, late-stage symptoms, such as swelling and curling of the fingers, can occur.
• Knees: The knee is the area most commonly affected by OA, with primary symptoms being pain and stiffness. These symptoms can make it difficult to walk, rise up from a seated position, or get in and out of cars or bathtubs.
• Hips: Hip osteoarthritis often presents with stiffness and pain localized in the hip area. However, some people also feel pain in their groin area, buttocks (glute muscles), inner thighs, or knees.
• Spine: OA in the spine can cause neck or lower back pain and stiffness. The stress on these areas can also put excess pressure on the nerves around the spine, causing numbness or tingling in the arms or legs. Severe nerve impairment can lead to issues with urination or bowel movements (incontinence).

Complications from osteoarthritis

Because it is a progressive disease, the symptoms of osteoarthritis often worsen over time. This can lead individuals with the condition to experience chronic pain⁸. Some people also experience the following complications^[15] or secondary conditions as a result of their OA:

• Negative mental health effects: Joint pain, stiffness, and difficulty moving can make usual tasks difficult and frustrating. OA has been associated with an increased risk of depressive symptoms and suicidal thoughts. If you or a loved one experiences suicidal thoughts or actions, call the National Suicide Prevention Lifeline at 1-800-273-8255.
• Trouble sleeping: The pain caused by OA can disrupt normal sleeping patterns. This can result in additional problems, such as memory loss and mood changes.
• Cardiovascular (heart) disease: Recent studies^[16] suggest the risk of having a heart attack is significantly increased in people with OA or other types of arthritis.