What Is Arthritis? Types, Causes, Symptoms, and Treatment

What Is Arthritis?

Arthritis is not a single disease but an umbrella term for more than 100 different conditions that cause joint pain, stiffness, and inflammation. It is one of the most common chronic health conditions worldwide — affecting over 350 million people globally and more than 58 million adults in the United States alone.

The word arthritis comes from the Greek arthron (joint) and itis (inflammation). While it can affect people of any age, arthritis is more prevalent in older adults, and the risk of many types increases with age.

The Two Most Common Types

Osteoarthritis (OA) — Wear and Tear

Osteoarthritis is the most common form, affecting more than 32 million Americans. It occurs when the cartilage — the firm, slippery tissue that cushions the ends of bones at joints — gradually breaks down. As cartilage deteriorates, bones begin to rub together, causing pain, swelling, and reduced range of motion. In advanced stages, bone spurs (osteophytes) may form.

OA most commonly affects the knees, hips, hands, and spine. It develops gradually over years and is strongly associated with age, previous joint injury, obesity, and repetitive joint stress from occupation or sport.

Rheumatoid Arthritis (RA) — Autoimmune Attack

Rheumatoid arthritis is an autoimmune disease in which the immune system mistakenly attacks the synovium — the lining of the membranes that surround the joints. The resulting chronic inflammation damages not only the cartilage and bone within the joint but can affect body systems beyond the joints, including the skin, eyes, lungs, heart, and blood vessels.

RA affects about 1.3 million Americans and is 2–3 times more common in women. It typically begins between ages 30 and 60. Unlike OA, RA frequently affects multiple joints symmetrically (both hands, both knees) and is associated with systemic symptoms like fatigue, fever, and loss of appetite.

Other Important Types

• Psoriatic arthritis: Joint inflammation accompanying the skin condition psoriasis. Affects about 30% of psoriasis patients.
• Gout: Caused by uric acid crystal deposits in joints, most often the big toe. Produces sudden, severe attacks of pain, redness, and swelling.
• Ankylosing spondylitis: Primarily affects the spine, causing inflammation that can lead to vertebrae fusing together.
• Lupus: A systemic autoimmune disease that can cause arthritis-like joint symptoms among many other manifestations.
• Juvenile idiopathic arthritis: The most common form of arthritis in children.

Symptoms

Common symptoms across types include:

• Joint pain, which may be dull, aching, or sharp
• Stiffness, especially in the morning or after rest
• Swelling and warmth around affected joints
• Reduced range of motion and difficulty with everyday activities
• Joint deformity in advanced cases

RA specifically often includes morning stiffness lasting more than an hour, profound fatigue, and episodes of flare (worsening) and remission.

Diagnosis

Diagnosis typically involves:

• Medical history and physical examination of affected joints
• Blood tests (for RA: rheumatoid factor, anti-CCP antibodies, inflammatory markers like CRP and ESR)
• Imaging: X-rays (show joint damage), MRI or ultrasound (detect early inflammation)
• Joint fluid analysis (especially for gout — microscopy reveals uric acid crystals)

Treatment

Non-Pharmacological

• Physical and occupational therapy: Exercise preserves joint function; therapists teach joint protection techniques.
• Weight management: Each pound of excess weight adds approximately 4 pounds of force on the knees. Weight loss is among the most effective interventions for knee OA.
• Hot and cold therapy: Heat relaxes muscles; cold reduces acute swelling and pain.
• Assistive devices: Braces, canes, and ergonomic tools reduce joint stress.

Medications

• Analgesics: Acetaminophen and topical NSAIDs for pain relief (OA).
• NSAIDs: Ibuprofen, naproxen — reduce both pain and inflammation.
• Corticosteroids: Injected or oral, for acute flares.
• DMARDs (Disease-Modifying Anti-Rheumatic Drugs): For RA — methotrexate is the anchor therapy, slowing disease progression.
• Biologics: TNF inhibitors (adalimumab/Humira, etanercept/Enbrel) and other targeted therapies have revolutionized RA treatment, achieving remission in many patients.
• JAK inhibitors: Newer oral medications (tofacitinib, baricitinib) that block inflammatory signaling pathways.

Surgery

For severe joint damage unresponsive to other treatment, joint replacement surgery (arthroplasty) can restore function. Total knee and hip replacements are among the most common and successful surgical procedures performed today.