What Causes Arthritis?

If you're a senior living with arthritis and finding your mobility restricted as a result, you might wonder what you did to deserve this lucky outcome of aging, while your sister or best friend seems to be enjoying her retirement years without a single mention of joint pain.

But in fact, although as many as one in three older adults has arthritis, it's not an inevitable part of getting older. Understanding the factors that can contribute to your risk for arthritis—including genetics, previous injuries, being overweight, and repetitive joint stress—is the first step in either preventing or managing this difficult condition.

What Is Arthritis?

Arthritis isn't a single disease but a general term for a long list of conditions that cause joint pain, swelling, and stiffness. More than 100 joint-related conditions fall under the arthritis umbrella, which literally means "joint inflammation."

The most prevalent type of arthritis is osteoarthritis, while other common types are rheumatoid arthritis and psoriatic arthritis. Osteoarthritis happens when the tissues in a joint break down, damaging tendons and ligaments, the lining of the joint (synovium), and the bone, per the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS).

How Does Arthritis Affect Your Joints?

In a healthy joint, a covering of strong, flexible connective tissue called cartilage reduces friction between the bones and helps them to move freely. The synovial membrane, which lines the joint, produces synovial fluid to lubricate the joint. Meanwhile, the ligaments connect bones together and the tendons attach muscles to bones, creating a supportive structure to keep joints stable.

The joint becomes the battleground with arthritis, says Diana Girnita, M.D., Ph.D., board-certified in rheumatology and founder of Rheumatologist OnCall in Irvine, CA. "In osteoarthritis, the smooth cartilage that caps the ends of your bones gradually wears away, so bone starts rubbing against bone. The body responds by forming little bony spurs, the joint space narrows, and you get pain, stiffness, and grinding."

Does Aging Cause Arthritis?

According to the World Health Organization (WHO), about 528 million people worldwide live with osteoarthritis, and about 73% of them are older than 55 years.

Age doesn't directly cause arthritis, but it is the biggest risk factor, notes Dr. Girnita. "The cumulative wear of years adds up," she says. A combination of repetitive joint use, decreased tissue repair capacity, and age-related muscle loss leads to a breakdown of the protective cartilage around the joint that the body can't rebuild quickly enough as you get older.

Does Being Overweight Cause Arthritis?

The impact of being overweight on your joints is two-fold, says Dr. Girnita. The first is mechanical: "Your knees absorb several times your body weight with each step, so even a modest amount of extra weight translates into a large amount of additional force across the joint over the course of a day," she says.

There's also a chemical component. "Fat tissue is metabolically active and releases inflammatory substances that can drive joint inflammation throughout the body, not just in the weight-bearing joints," Dr. Girnita notes. The good news is that this cuts both ways: "Losing even a modest amount of weight meaningfully reduces the load and the inflammation, and my patients often feel the difference in their joints well before the scale shows a big change," she adds.

Common Risk Factors for Arthritis

Alongside the natural aging process, other factors can increase the risk for arthritis, says Dr. Girnita. "Some of these factors you can't change, but several you can, which is where I focus my patients' attention," she adds. Factors include:

• Bone deformities. If you're born with malformed joints or defective cartilage, uneven pressure and mechanical joint issues can increase risk for cartilage wear and arthritis.
• Excess weight. As noted, "being overweight is a major and modifiable factor, particularly for the knees and hips," says Dr. Girnita.
• Genetics. "Osteoarthritis often runs in families," she says. Depending on the joint that is affected, research estimates arthritis heritability is between 40% and 70%. Studies have identified hundreds of genetic variations linked to joint deterioration.
• Injury. Previous joint injuries raise your odds of developing arthritis later in life. "A knee you tore up playing sports at 20 can become the arthritic knee at 50," Dr. Girnita notes.
• Repetitive joint stress and overuse. "Any occupation or activity that puts repetitive stress on the same joints raises your risk," she says. That includes heavy lifting, kneeling, or repetitive motion.
• Sex and hormonal changes. If you are female and post-menopausal, your odds of arthritis are higher. A sharp drop in protective estrogen levels with menopause can lead to greater stress on joints and systemic inflammation, say researchers.

Which Joints Are Most Affected by Wear-and-Tear Arthritis?

Technically, arthritis can affect any joint in the body, but some are more likely to be targeted than others. "The most common joints affected by arthritis are the hips, knees, hands, spine, and shoulders," says Jeff Sodl, M.D., an orthopedic surgeon with Providence St. Joseph Hospital in Orange, CA. "These major joints are responsible for body movement and are prone to overuse and injury."

These are a few ways arthritis can show up in different parts of the body:

• Foot and ankle arthritis. Arthritis can affect any of the 30-plus joints in your feet and ankles, leading to pain, stiffness, or reduced range of motion.
• Hand and finger arthritis. When you have arthritis in your hands or fingers, you may experience pain, stiffness, swelling, and bumps on your finger joints.
• Hip arthritis. Common symptoms of arthritis in the hip include a deep ache in the groin or buttocks, stiffness after sitting or when waking up in the morning, and feeling like the hip joint "locks" or sticks during movement.
• Knee arthritis. Arthritis in the knee typically causes pain, swelling, and stiffness of the knee joint. Other signs include clicking or grinding noises when you move the joint, difficulty walking, and knee weakness or buckling.
• Spine arthritis. Spine arthritis can occur anywhere along the spine but is most common in the lower back and neck, causing pain and stiffness.

What Causes Other Types of Arthritis?

Rheumatoid arthritis and psoriatic arthritis are considered to be autoimmune diseases. "In rheumatoid arthritis and psoriatic arthritis, the immune system attacks the lining of the joint, causing swelling, warmth, and—if untreated—erosion and destruction of the joint over time," explains Dr. Girnita. "As with osteoarthritis, you end up with a joint that's stiff, often swollen, painful to move, and progressively less able to do its job."

Axial spondylitis (axSpA) is a chronic inflammatory arthritis that mainly affects the spine and pelvis, causing pain, stiffness, and potential bone fusion. Inflammatory back pain and early morning stiffness are associated with this type of arthritis.

Gout is another common and painful type of inflammatory arthritis, caused by a buildup of the waste product uric acid, forming sharp crystals inside and around the joints.

Can You Prevent Arthritis?

Because arthritis is multi-factorial and may have a genetic component, there is no sure-fire way to prevent it. However, there are things you can do to reduce the risk of developing it or manage your symptoms if you already have it. "Lifestyle adjustments such as proper weight management, muscle preservation, low-impact exercises for mobility, stretching, anti-inflammatory diets, and managing chronic medical conditions will help," says Dr. Sodl.

When to See a Healthcare Provider

Addressing arthritis symptoms early may help prevent joint damage and mobility problems from worsening. Talk to your doctor if you have persistent or increasing joint pain, swelling, warmth or redness; difficulty bearing weight; or reduced mobility that interferes with daily activities. Sudden severe pain or a hot, swollen joint should be evaluated promptly. Together, you and your doctor will come up with an action plan that keeps symptoms at bay.