Arthritis Explained: Types, Causes, And Treatments

If you think arthritis is something you won't need to worry about until you're much older, think again. According to the Centers for Disease Control and Prevention (CDC), 54 million Americans have been diagnosed with arthritis, and 60% of them are of working age (18 to 64). In fact, arthritis is a leading cause of disability, and 8 million adults aren't able to work because of their arthritis. Many younger individuals may not even realize that their achy back or stiff knees are actually arthritis.

While we often think of arthritis as a single medical issue, it's actually an umbrella term for a number of conditions affecting the joints. The most common forms include osteoarthritis, rheumatoid arthritis, and gout. Many other conditions can include arthritis as a symptom. According to the CDC, "symptoms of arthritis are pain, aching, stiffness, and swelling in or around the joints." While symptoms can vary from person to person and day to day, the CDC noted that one in four Americans with arthritis experiences severe joint pain. 

While arthritis can't necessarily be prevented, there are things you can do to protect the health of your joints and minimize your risk. And for those already living with some form of arthritis, there are a variety of treatment options available to minimize pain and improve quality of life.

Joint anatomy and the two types of arthritis

To better understand arthritis, 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.

Different types of arthritis can be placed in one of 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 (via UpToDate). 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.

Osteoarthritis is the most common type of arthritis

Osteoarthritis (OA) is the most prevalent form of arthritis (via the Osteoarthritis Action Alliance). Of the 54.4 million Americans with arthritis, 32.5 million of them have osteoarthritis. 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 OA 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.

Osteoarthritis is considered a form of degenerative or mechanical arthritis — a "wear and tear" condition (via the Mayo Clinic). Over time, the cartilage that cushions the ends of the bones in a joint wears away, causing the bones to rub against one another and leading to pain, stiffness, and reduced range of motion. While any joint can be affected, the knees, hips, spine, and hands are most vulnerable to cartilage damage. The breakdown of the joint can happen simply as a result of getting older, or because of injuries or repeated stress on the joint. In addition to risk factors outside our control (such as age, sex, and genetic predisposition), certain occupations and sports may increase the likelihood of osteoarthritis. Heavier individuals and those with certain medical conditions, including diabetes, are also at higher risk.

Rheumatoid arthritis is the most common form of inflammatory arthritis

Rheumatoid arthritis (RA) is another form of joint disease that can leave people feeling stiff and achy (via the Mayo Clinic). RA is an autoimmune disease in which the immune system mistakenly begins attacking the synovial membranes that surround the joints. The resulting inflammation eventually deforms and damages the joint. Joints may also shift out of place. It's unclear what exactly triggers the body to begin attacking healthy joint tissue, but genetics likely plays a role. RA tends to begin in small joints (such as the fingers and toes) and then spreads to the wrists, ankles, elbows, knees, hips, and shoulders. The damage is usually symmetrical, affecting the same joint on both sides of the body. In about 40% of individuals with RA, the condition also leads to inflammation and damage to other parts of the body, such as the skin, lungs, and heart. RA can strike at any time, but most often appears in middle age. The pain isn't necessarily constant, however. Many people with RA have flare-ups of inflammation followed by periods of remission in which inflammation subsides and they're symptom-free. RA affects approximately 0.5–1% of people in the United States (via UpToDate). Women are twice as likely as men to have RA.

Gout is a "medieval" arthritis that's still around

Most people have a vague idea of what gout is but assume it's a long-extinct condition that once upon a time affected the overindulgent royalty of medieval Europe. The truth is that this type of arthritis is actually still very common. WebMD estimates that gout affects 4% of the U.S. population — more than 8 million Americans. And rates of gout are on the rise.

According to the Mayo Clinic, gout is a form of arthritis marked by sudden and severe pain in a particular joint, often the big toe. Gout is caused by needlelike urate crystals that form in joints or the surrounding tissue. Urate crystals are made of uric acid, a byproduct of breaking down substances in food called purines. Some foods — such as red meat, organ meats, beer, fish, and seafood — contain high levels of purines. (Hence the connection to gluttonous kings of old). If you produce too much uric acid when breaking down purines or your kidneys have a hard time getting rid of the uric acid you produce, it can build up and form urate crystals. Gout may have a genetic component, but many other factors can increase your risk for this form of arthritis. Eating a diet high in purines, being overweight, having certain medical conditions (including high blood pressure and diabetes), and taking some types of medications (like beta blockers and diuretics) can also up your chances of getting gout. Gout occurs more often in men, and they tend to get it earlier (between 30 and 50). Women are most likely to get gout after menopause, when changes in hormone levels cause their uric acid levels to rise.

Ankylosing spondylitis can cause debilitating arthritis in your spine

According to WebMD, "ankylosing spondylitis (AS) is a rare type of arthritis that causes pain and stiffness in your spine." Also known as Bechterew disease, the condition usually begins in the sacroiliac joints of the lower back and can spread up the spine to the neck or to other joints in the body. AS is an inflammatory arthritis and, over time, can cause the vertebrae in your spine to fracture or fuse together. While the exact cause of AS is unknown, those with a genetic variation that causes their bodies to produce a protein called HLA-B27 appear to be at much higher risk. It's believed that the HLA-B27 protein may stimulate the immune system to attack a common bacteria in the body, thereby triggering AS.

Although AS is not as common as other forms of arthritis, it still affects as much as 0.5% of the population — more than 1.6 million Americans (via the Johns Hopkins Arthritis Center). About 5% of individuals with the HLA-B27 gene will get AS. The condition is more common in men. About 80% of those with AS will begin experiencing symptoms at or before age 30, and only 5% will begin experiencing symptoms at age 45 or older.

Kids can get arthritis too

While most people think of arthritis as an ailment that only affects older individuals, even kids can experience joint disease. According to the American College of Rheumatology, about 300,000 American children have some form of diagnosed arthritis. Juvenile arthritis (JA) affects about 1 in every 1,000 children. Symptoms can appear at any time during childhood or adolescence but are rarely seen in infants younger than six months.

Like its adult counterpart, JA isn't a single condition. Instead, it's a term encompassing any form of arthritis that appears before age 16 (via the Arthritis Foundation). Arthritis in children is almost always of the inflammatory type and usually caused by an autoimmune or autoinflammatory condition. Juvenile idiopathic arthritis is the most common form of JA and includes several subtypes. Other common forms of JA include juvenile lupus, juvenile myositis, juvenile scleroderma, and vasculitis. Because JA affects individuals who are still physically maturing, if not properly managed it can lead to growth problems and issues with bone development (via the Mayo Clinic). Some treatments for JA, such as corticosteroids, can also cause growth problems. Still, according to the Arthritis Foundation, an early and aggressive treatment plan can lead to remission and help prevent or mitigate related long-term health issues.

Arthritis can be triggered by infections

While not super common, in some cases an infection can trigger arthritis. Septic arthritis occurs when the infection is in the joint itself (via Johns Hopkins Medicine). The infection usually travels through the bloodstream to the joint, but injections into, surgery on, or injuries to a joint can also introduce pathogens that cause infection in the joint. Staphylococcus aureus is the bacteria that causes most cases of septic arthritis, though others including Haemophilus influenzae, Streptococci (strep), and Gonococci (the bacteria that causes gonorrhea) can also travel to the joints. HIV and other viruses can lead to septic arthritis as well. If not treated promptly, septic arthritis can destroy the cartilage in a joint.

In reactive arthritis, an infection elsewhere in the body triggers arthritis even though the infection hasn't spread to the joint itself (via the Mayo Clinic). Infections in your intestines, urinary tract, or genitals are most likely to trigger reactive arthritis. This includes the bacteria that cause chlamydia and those that cause "stomach bugs" (including Salmonella, Shigella, Campylobacter, and Clostridium difficile). In some cases, individuals may not even realize they have the underlying infection until arthritis symptoms appear. Formerly known as Reiter's syndrome, reactive arthritis is most likely to occur in the knees, ankles, and feet.

There are many other types of arthritis, and arthritis can be a symptom of many chronic conditions

Although the most common types of arthritis have already been discussed, there are many others that, collectively, affect millions of individuals. For example, psoriatic arthritis (PsA) is a condition that affects about 1.5 million Americans — according to the Johns Hopkins Arthritis Center, one in three people with the skin condition psoriasis will eventually get PsA. The center noted that "most people develop psoriasis about 10 to 20 years before being diagnosed with psoriatic arthritis." If not properly managed, this inflammatory arthritis can cause severe joint and tendon damage.

Lupus is another autoimmune disease that can cause achy, swollen joints (via WebMD). While not usually severe, arthritis is very common among those with lupus. The arthritis may be temporary or permanent. Ehlers-Danlos syndrome (EDS) is a cluster of genetic disorders affecting the connective tissues of the body (via the Arthritis Foundation). Not surprisingly, arthritis is common among individuals with EDS, especially those with the hypermobility type (hEDS). While having super flexible joints might sound like a good thing, people with hEDS are prone to joint dislocations, chronic pain, and degenerative joint disease because of their condition.

Other conditions that can feature arthritis as a symptom include fibromyalgia, chronic fatigue syndrome, hemochromatosis (when iron builds up to toxic levels in the body), inflammatory bowel disease, Lyme disease, and osteoporosis (via the Arthritis National Research Foundation).

Symptoms and complications of arthritis

Of course the hallmark symptoms of arthritis are joint pain and stiffness, sometimes accompanied by swelling, tenderness, and reductions in range of motion (via UpToDate). Where and under what circumstances pain arises can provide clues to what type of arthritis someone has. Noninflammatory (degenerative) arthritis can occur on one or both sides of the body and is usually aggravated by moving or bearing weight on the affected joints. By contrast, inflammatory arthritis causes pain at rest, especially first thing in the morning (via WebMD). Inflammatory arthritis is also usually symmetrical, affecting the same joint on both sides of the body. Other common symptoms of osteoarthritis, the most common type of arthritis, include joints that feel or sound "crunchy" and painful lumps of bone called bone spurs that form around joints.

If not well-managed, arthritis — especially the inflammatory forms — can lead to serious complications (via the Mayo Clinic). Rheumatoid arthritis, for instance, can increase your risk for osteoporosis, lung disease, heart problems, and lymphoma. Those with gout may get extremely painful kidney stones if urate crystals build up in the urinary tract (via the Mayo Clinic). In severe cases of ankylosing spondylitis (AS), the vertebrae may fuse, preventing normal movement of the spine and rib cage and affecting posture and breathing (via the Mayo Clinic). AS can also lead to eye inflammation and blurred vision, heart problems, and compression fractures in the spine.

Diagnosing arthritis

Many people may be living with arthritis and not realize it. According to the Arthritis Foundation, while 54 million American adults have been told by a doctor that they have some form of arthritis, as many as 37 million more may have joint disease that hasn't yet been formally diagnosed. Diagnosing arthritis usually requires several steps. A doctor can often confirm you have arthritis simply by doing a physical exam and asking questions about your medical history (via UpToDate). But determining the cause of the arthritis can be a little trickier. Imagining such as x-rays, ultrasound, MRI, and CT scans can be used to visualize the joint and check for bone erosion, injuries, and inflammation. If a doctor suspects the arthritis is autoimmune in nature, blood tests can be ordered to check for particular auto-antibodies. In the case of rheumatoid arthritis, for instance, a sample of blood will be tested for rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP) antibodies. Synovial fluid can also be extracted from a joint in a procedure called arthrocentesis and tested. This is especially useful for diagnosing arthritis caused by inflammation or infection.

Medications can help treat the pain of arthritis

There are a number of medications that can reduce the joint pain and inflammation of arthritis. 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 (via the Mayo Clinic). Unfortunately, NSAIDs can cause irritation and damage to your gastrointestinal 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.

For those with inflammatory forms of arthritis, corticosteroids (either taken orally or given as injections) can reduce inflammation and slow joint damage. But long-term corticosteroid use carries many risks, including weight gain, brittle bones, and increased risk of diabetes. Disease-modifying antirheumatic drugs (DMARDs) can prevent permanent tissue damage in those with rheumatoid arthritis, but they also increase your risk of infections. Septic and reactive arthritis require antibiotics to clear up the underlying infection (via the Mayo Clinic). In many cases, intravenous antibiotics are given prior to a course of oral antibiotics, and total treatment time can last from two to six weeks.

Physical therapy can help people manage arthritis

According to WebMD, many people with arthritis 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 arthritis 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."

Strengthening and improving the range of motion in joints are key objectives of 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 inflammation and pain, as well as how to modify their homes and workplaces to make pain-free movement easier. Additionally, therapists can recommend assistive devices like splints and walking aids, bath stools, and grab bars. PT can be particularly valuable after joint surgery, helping individuals improve joint mobility and ensure proper healing.

Joint surgery is also an option

For arthritis that causes severe pain and doesn't respond well to medication or physical therapy, joint surgery may be necessary (via WebMD). But such procedures are often a last resort, since they're invasive and carry their own risks. For those with osteoarthritis, arthroscopy is one option. 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 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. These procedures are also options for those with other types of arthritis, including rheumatoid arthritis (via WebMD).

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. Thousands more surgeries are performed to replace ankles, wrists, shoulders and elbows.

Keeping joints healthy

As the Sarasota Memorial Health Care System pointed out, "there is not a one-size-fits-all approach to arthritis prevention, because there are many types of arthritis and each has different risk factors." But since osteoarthritis is a "wear and tear" disease, it's the easiest to guard against. Strategies to bulletproof your joints against osteoarthritis include maintaining a healthy weight (since excess pounds can put extra stress on joints), being physically active and using proper form when exercising, and avoiding activities during work or leisure time that put repetitive stress on your joints. It's also important to see a doctor if you suspect you may have the beginnings of osteoarthritis, since early intervention can slow the progression of the condition.

Since many forms of inflammatory arthritis appear to be driven largely by genetic factors, there's little you can do to prevent them (via WebMD). In the case of rheumatoid arthritis (RA), however, avoiding cigarettes and ensuring your gums stay healthy could reduce your risk, as both smoking and periodontal disease have been shown to significantly increase your risk for RA. For those with gout, limiting or avoiding alcohol, drinking plenty of water, and eating a low-purine diet can help prevent flare-ups (via Arthritis-Health).