Osteoarthritis Explained: Causes, Symptoms, And Treatments

While we often think of arthritis as a single medical issue, it's actually an umbrella term for a number of conditions that cause pain and swelling of the joints. The most common form of arthritis is osteoarthritis, in which the cartilage in joints breaks down, causing the bones to rub against one another (via the Mayo Clinic). 

According to the Osteoarthritis Action Alliance, osteoarthritis is the third most rapidly increasing cause of disability in the United States. The pain and stiffness associated with osteoarthritis can be extreme: About 25% of adults with arthritis have severe pain and 44% aren't able to do their usual activities because of the condition. Not surprisingly, having osteoarthritis also increases a person's risk for depression and anxiety. Osteoarthritis also carries a heavy economic burden, and is one of the most costly chronic conditions. Each year, the condition costs Americans $17 billion in indirect costs (such as lost work days) and $65 billion in direct medical costs. On a personal level, having osteoarthritis costs an individual about $11,000 a year.

But what exactly causes osteoarthritis, who's most at risk, what are the treatment options, and is there anything you can do to safeguard your joints?

Joint anatomy

To better understand osteoarthritis, you first need to know a little bit about joints and their anatomy. A joint is where two or more bones meet (via the University of Rochester Medical Center). Most joints are mobile and are classified by the type of motion they provide. Ball-and-socket joints (think: shoulders and hips) allow bones to move in all directions, while hinge joints like the elbow and knee allow only bending and straightening. Pivot joints like the neck allow for limited rotation, while ellipsoidal joints like the wrist allow for all movements except rotation. A type of slippery connective tissue called cartilage covers the ends of bones where they meet at a joint, reducing friction as they move. Joints are encased in a thin layer of tissue called the synovial membrane. Inside the joint, synovial fluid helps lubricate the bones so that they can move more easily. Fluid-filled sacs called bursas provide cushioning between the structures that make up a joint. Tendons (which connect muscles to bones) and ligaments (which connect bones to other bones) provide structure to and stabilize the joint.

According to the Cleveland Clinic, "cartilage is made up of two main elements: cells within it known as chondrocytes and a gel-like substance called matrix, composed mostly of water and two types of proteins (collagen and proteoglycans)." These components work together to give cartilage its strength and cushioning properties.

Osteoarthritis causes physical damage to the joints

There are many types of arthritis, and they can be divided into two broad categories based on how damage is done to the joint. As the name implies, inflammatory arthritis causes inflammation in the joint that prevents its proper functioning. By contrast, noninflammatory arthritis (also sometimes referred to as degenerative or mechanical arthritis) arises when the structures that make up the joint wear down or are otherwise physically damaged (via UpToDate). Osteoarthritis falls into this second category, and is often considered a "wear and tear" condition. Over time, the cartilage that cushions the ends of the bones in a joint wears away, causing bones to rub against one another, leading to pain, stiffness, and reduced range of motion (via the Mayo Clinic).

There are two forms of osteoarthritis. As WebMD notes, primary osteoarthritis is caused by the gradual breakdown of cartilage. Although it can happen in any joint, the fingers, thumbs, spine, hips, knees, and big toes are most commonly affected. Primary osteoarthritis is the more common of the two forms. Secondary osteoarthritis, on the other hand, occurs when the cartilage is damaged by another medical condition. Common causes of secondary osteoarthritis include obesity (which puts added stress on joints), injuries, improper healing after a surgery, overuse from a particular occupation or hobby, and congenital abnormalities in joint anatomy. Diabetes and other forms of arthritis, including gout and rheumatoid arthritis, can also cause osteoarthritis over time.

But inflammation still plays a role in osteoarthritis

Although osteoarthritis is considered a degenerative (rather than inflammatory) type of arthritis, that doesn't mean inflammation doesn't play an important role in the condition.

As a 2013 paper published in Therapeutic Advances in Musculoskeletal Disease noted, joint inflammation and synovitis (inflammation of the membrane that lines the inside of the joint) are present in many people with osteoarthritis. While the exact nature of the relationship between inflammation and osteoarthritis is still unknown, the paper's authors speculate that the immune system's natural response to physical joint damage may create a state of chronic inflammation that only further degrades the joint. Inflammatory immune molecules such as cytokines, chemokines, and adipokines may become overly activated in people with osteoarthritis.

According to a 2020 paper published in Medicine and Pharmacy Reports, oxidative stress plays a big role in osteoarthritis. Oxidative stress occurs when there's an imbalance between pro-inflammatory molecules called reactive oxygen species (ROSs) and anti-inflammatory antioxidants in the body. Substances that produce ROSs can be found in food and in our environment, and are also created as the byproduct of natural chemical processes in the body. In the case of osteoarthritis, ROSs build up in the cartilage and fluid surrounding joints, causing damage on a cellular level.

Genes also matter when it comes to osteoarthritis

Although osteoarthritis isn't an inherited condition, experts now believe that genes play a critical role in determining an individual's risk for the condition. As MedlinePlus explained, there's a balance between the building and breakdown of bone and cartilage, and if there's more breakdown than repair, the eventual end result will be osteoarthritis. They noted that "the genes whose expression influences osteoarthritis risk are typically involved in the formation and maintenance of bone and cartilage." Variations that either "silence" the genes involved in these processes or cause them to be expressed in the wrong way will increase an individual's risk for osteoarthritis. There are likely a large number of genes that can affect osteoarthritis risk, and "in most cases, multiple genetic changes, each with a small effect, combine to increase the risk of developing the disorder" (per MedlinePlus).

A 2020 paper published in Osteoarthritis and Cartilage noted that so far 90 genes have been identified as contributors to osteoarthritis risk, although the total number is likely much higher. Many of these genes also play a role in determining height and hip shape. Differences in RNA — the molecule that "reads out" the DNA of our genes — also impact cartilage health and thus osteoarthritis risk.

Who gets osteoarthritis?

Osteoarthritis is the most prevalent form of arthritis. Of the 54.4 million Americans with arthritis, 32.5 million of them have osteoarthritis (via the Osteoarthritis Action Alliance). Generally considered an unavoidable part of aging, it's true that the majority of people with osteoarthritis are older adults. But 12% of people with osteoarthritis are under 45, and 57% are younger than 65. Although 62% of people with osteoarthritis are women, the majority of those with the condition under age 45 are men.

There are many risk factors that may increase a person's chances of having osteoarthritis. Many of these, however, are completely outside our control. These include older age, being female, having certain genes, and having structural anomalies in certain joints. Other risk factors include obesity and occupations or hobbies that put repeated stress on particular joints. Injuries to the joint — even those that occurred long ago and seem to have healed normally — may lead to osteoarthritis in the future (via the Mayo Clinic). Diabetes (specifically, high blood sugar levels) and high cholesterol can damage the resilience of cartilage on a cellular level and impede proper blood flow to the joint. The drop in estrogen that comes with menopause also puts older women at greater risk of osteoarthritis, particularly in the knees (via the Cleveland Clinic).

Osteoarthritis symptoms

Whatever the underlying cause or combination of causes, osteoarthritis symptoms usually develop slowly and get gradually worse over time (via the Mayo Clinic). Pain, particularly during or after movement, is one of the hallmark symptoms of the condition, as is joint stiffness. Joints are most likely to be stiff first thing in the morning or after a period of inactivity. Joints and the area around them may be swollen and tender to even light touch. Moving the affected joint may create an audible popping or cracking and create a grating sensation. Arthritic joints also often lose range of motion. Painful bone spurs may also develop around the affected joints. If the pain and stiffness are severe, it can make daily tasks like walking, putting on clothes, or preparing a meal extremely difficult. It can also disrupt sleep.

But just because you have wear and tear on your joints doesn't mean you'll experience symptoms (or that your symptoms will be severe or ever-present). In fact, according to the Cleveland Clinic, while roughly 80% of adults 55 and older have evidence of osteoarthritis based on x-ray imaging, only about 60% have noticeable symptoms. In a 2021 study published in BMC Musculoskeletal Disorders, only about one-third (34%) of those surveyed had chronic pain.

How is osteoarthritis diagnosed?

According to WebMD, x-ray imaging is the main tool for diagnosing osteoarthritis. Doctors generally look for "loss of joint cartilage, narrowing of the joint space between adjacent bones, and bone spur formation." Doctors also consider the nature of the symptoms (such as where pain occurs, the type of pain, and how long it lasts) when making a diagnosis. Arthroscopy is a surgical procedure in which a doctor inserts a small, flexible tube into the joint space. By inserting a tiny camera through the tube, the doctor can see inside the joint and spot abnormalities of and damage to the cartilage. (In addition to helping diagnose osteoarthritis, arthroscopy is also sometimes used to repair joint damage.)

An important task when diagnosing osteoarthritis is excluding other types of arthritis or other medical conditions that may be causing the symptoms. X-rays are also useful for excluding other conditions, as are certain blood tests. Arthrocentesis, in which a needle is used to remove some of the synovial fluid from inside a joint, is commonly performed to check for gout, infection, and other causes of inflammatory arthritis.

Magnetic resonance imaging (MRI) can provide much more detailed images of the joint. Although x-rays are usually sufficient for diagnosing osteoarthritis, the detail provided by MRI can help doctors better understand more complex cases of osteoarthritis and formulate a treatment plan (via the Mayo Clinic).

Medications for osteoarthritis

As the Cleveland Clinic notes, "unlike other forms of arthritis where great advances have been made in recent years, progress has been much slower in osteoarthritis. There are no medications yet available that have been shown to reverse or slow the progression of osteoarthritis." There are, however, medication options that can help manage osteoarthritis pain.

Over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Advil) or naproxen (Aleve) can be useful, although higher-strength prescription versions may be necessary. Unfortunately, NSAIDs can cause irritation and damage to your GI tract and may increase your risk for heart attack or stroke. NSAIDs also come in gels or creams that can be applied topically. Other topical options include creams with menthol or capsaicin (the compound that gives peppers their spice). These counterirritants may interfere with the transmission of pain signals, providing temporary relief. Acetaminophen (Tylenol) can also help with mild to moderate pain, but taking too much can cause significant liver damage. Interestingly, the antidepressant duloxetine (Cymbalta) has also been shown to assist with the management of chronic pain and has been approved by the Food and Drug Administration (FDA) for that use (via the Mayo Clinic).

Injections for osteoarthritis

Another option for osteoarthritis are injections directly into the joint. Corticosteroids are one commonly used group of drugs. Corticosteroids reduce inflammation inside an arthritic joint and generally work faster and are more effective than oral NSAIDs. The effects aren't permanent, however, and corticosteroids don't actually repair cartilage or slow the progression of osteoarthritis. Because they're injected directly into the joint, they have fewer, more localized side effects than oral medications, but they still carry risks. These include infections in the joint, damage to joint tissue and surrounding ligaments, and (paradoxically) increased inflammation. Plus, there's a limit to how often you can get corticosteroid injections. Experts recommend limiting injections to no more than once every three or four months; individual joints should not receive more than about four injections total (via WebMD).

Hyaluronic acid (HA) is another substance often injected into arthritic joints (per WebMD). HA helps lubricate joints and your body produces it naturally. But in joints with osteoarthritis, HA becomes thinner and less able to cushion the joint. Injecting HA can supplement the HA your body produces and is therefore sometimes referred to as viscosupplementation. For some, HA injections are more effective than oral painkillers or corticosteroid injections. Others — particularly older individuals and those with severe osteoarthritis — tend not to get good results with HA injections. There are several formulations of HA injections. Some are given as a single shot, while others are a series of three to five injections spaced a week apart.

Exercise for osteoarthritis

Reason #10,528 to exercise: it can help prevent or manage osteoarthritis. As Sarasota Memorial Hospital notes, "being physically active helps strengthen the muscles around your joints and improves flexibility — both of which are good for your joints. Exercise also can help you lose weight or maintain a healthy weight, which may also reduce arthritis risk." Striking a balance and getting plenty of variety are important, however, since doing activities that put a lot of heavy repetitive stress on a particular joint can actually increase your risk for osteoarthritis down the line.

It may seem counterintuitive, but for those who already have osteoarthritis, getting regular exercise can ease, rather than exacerbate, pain and stiffness (via WebMD). Exercise strengthens the muscles and connective tissues around joints, reducing the strain on the joint. Exercise can also improve range of motion and reduce stiffness in a joint. Getting heart rate up improves blood flow, which brings important nutrients to the joint. And of course, exercise can improve mood and sleep quality, two things that tend to suffer because of osteoarthritis pain. In addition to strength training, low-impact aerobic exercise (including walking and tai chi) is also essential. Aquatic exercise such as swimming and water aerobics are particularly beneficial because of water's buoyancy and the warmth provided by a heated pool.

Physical therapy and assistive devices

According to WebMD, many people with osteoarthritis are reluctant to move the affected joints because they want to avoid pain. But this lack of movement only makes joints stiffer and decreases their range of motion, creating a vicious cycle. But regularly attending physical therapy (PT) or occupational therapy (OT) can help those with osteoarthritis learn how to use their joints without further damaging them. The goal of these therapies is to "get a person back to the point where they can perform normal, everyday activities without difficulty."

As mentioned above, strengthening and improving the range of motion in joints are important keys to managing the symptoms of osteoarthritis, and these are often incorporated into PT and OT. Therapists show patients how to perform exercises that stretch and strengthen the joint while avoiding further damage. They can also instruct individuals on how to use heat and ice to reduce pain, as well as how to modify their homes and workplaces to make pain-free movement easier. Therapists can also recommend assistive devices like splints and walking aids, bath stools, and grab bars. Therapists can also help individuals with posture, joint alignment, and body awareness, which further helps patients protect their joints. PT can be particularly valuable after joint surgery, helping individuals improve joint mobility and ensure proper healing.

Foods for osteoarthritis

What role does nutrition play in bulletproofing your joints? According to a 2018 paper published in Rheumatology, diet can help individuals better manage their osteoarthritis. Getting all the micronutrients your body needs, especially omega-3 fats and vitamin K, gives your body the raw materials it needs to maintain joint health and combat inflammation. For overweight and obese individuals, a diet that promotes weight loss can be beneficial. A diet that lowers cholesterol levels can also help.

A few individual foods may be especially helpful. According to a 2013 article published in Science Direct, research suggests that sulforaphane, a compound released when eating broccoli, can slow down the destruction of cartilage in joints. Sulforaphane is present in other cruciferous vegetables as well, including Brussels sprouts and cabbage, but is particularly concentrated in broccoli. This compound "blocks the enzymes that cause joint destruction by stopping a key molecule known to cause inflammation." 

Meanwhile, a 2011 paper published in Arthritis Research & Therapy states that epigallocatechin-3-gallate (EGCG), a polyphenol (plant compound) found in green tea, has powerful anti-inflammatory properties that may help prevent or better manage osteoarthritis. Extra-virgin olive oil is full of monounsaturated fatty acids which, according to a study published in 2018 in Arthritis Care & Research, help reduce the loss of joint space over time in arthritic knees.

Supplements and alternative medicine

There are a number of dietary supplements and forms of alternative medicine that claim to promote joint health, but are these actually useful for osteoarthritis? 

Glucosamine and chondroitin are natural compounds found in cartilage, so it makes sense that taking these two in supplement form could help arthritic joints. Studies of these supplements' effectiveness, however, have yielded mixed results. Although generally considered safe, glucosamine and chondroitin may raise blood sugar levels and interact negatively with blood thinners (via the Arthritis Foundation). Fish oil, rich in anti-inflammatory omega-3 fatty acids, is another supplement often used for osteoarthritis. In a 2020 paper published in Rheumatology Advances in Practice, researchers found that fish oil supplements significantly reduced osteoarthritis pain in overweight and obese individuals. Interestingly, the researchers also tested the efficacy of curcumin, an anti-inflammatory compound found in turmeric, and concluded that it had no effect on osteoarthritis pain.

Acupuncture may also offer pain relief for some people. Although Western medicine doesn't recognize the concept of balancing bodily energy on which this Eastern practice is based, it offers its own perspective on why acupuncture may work (via the Arthritis Foundation). The insertion of acupuncture needles triggers the release of endorphins, the body's natural painkiller. It also triggers production of the hormone cortisol, which has inflammation-fighting properties. Some researchers dismiss acupuncture's benefits as simply the placebo effect, but others counter that results are what matters, not how the results are achieved.

Surgical options for osteoarthritis

Joint surgery may be necessary to address severe osteoarthritis. But such procedures are often a last resort, since they're invasive and carry their own risks. 

Arthroscopy is one option (via WebMD). In this procedure, a surgeon inserts a thin, flexible scope into the joint via a small incision. Through the scope, the surgeon can smooth rough bone edges and remove damaged cartilage or bone fragments. While the procedure has a quick recovery time, its usefulness for osteoarthritis is very limited. In a total joint replacement (arthroplasty), the surgeon replaces the arthritic joint with an artificial metal or plastic one. While this procedure can greatly reduce pain and improve quality of life, it requires significant recovery time and the artificial joint will eventually wear out and need to be replaced with another. Joint fusion involves the use of pins, screws, plates, or rods to join two or more bones together. Although joint fusion can dramatically reduce pain, it reduces mobility and may cause osteoarthritis to spread to other joints as they try to overcompensate for the lack of mobility in the fused joint.

Knees and hips are the joints most likely to be replaced. According to data reported on by CNN in 2018, approximately 700,000 total knee replacements and 400,000 total hip replacements are performed in the United States each year (although not all of those are because of osteoarthritis). Thousands more surgeries are performed to replace ankles, wrists, shoulders and elbows.