Arthritis Basics

How common forms of arthritis differ, how they are evaluated, and when to seek care

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Arthritis is not one disease. It is a broad name for conditions that can cause joint pain, stiffness, swelling, inflammation, or loss of movement. Some forms mainly involve changes within the joint over time. Others are caused by the immune system, crystals, infection, or injury. Knowing the type matters because treatments that help one condition may not treat another.

This page provides general education, not a diagnosis or individual medical advice.

What is osteoarthritis? Types of arthritis How it is diagnosed Living with arthritis When to seek care Treatment options

What Is Osteoarthritis?

Osteoarthritis (pronounced os-tee-oh-arth-RY-tis, sometimes shortened to "OA") is a joint condition caused by the gradual breakdown of cartilage, the tissue that cushions the ends of bones. As cartilage wears down, the joint can become painful, stiff, and less flexible, especially with movement or after periods of rest. It's the most common form of arthritis, and it's different from rheumatoid or psoriatic arthritis, which are driven by the immune system rather than everyday wear on the joint.

Outside the US, and in some older or translated medical literature, this same condition is often called arthrosis (or osteoarthrosis). It's not a different disease, just a different regional name for osteoarthritis.

Common Types of Arthritis

Degenerative

Osteoarthritis

Osteoarthritis is the most common form of arthritis. It affects the whole joint, including cartilage, bone, the joint lining, ligaments, and nearby muscles. It becomes more common with age, but it is not simply an unavoidable part of getting older.

Pain often worsens with activity or prolonged use. Stiffness after rest may ease once the joint starts moving.

Usual care: exercise, physical therapy, medicines, braces or aids, selected procedures, and sometimes surgery.

Autoimmune

Rheumatoid Arthritis

Rheumatoid arthritis occurs when the immune system attacks tissues around the joints. It often affects several joints and may involve both sides of the body.

Early treatment matters because uncontrolled inflammation can permanently damage joints and affect other organs.

Usual care: a rheumatologist and disease-modifying medicines, with therapy and ongoing monitoring.

Inflammatory

Psoriatic Arthritis

Psoriatic arthritis is linked with psoriasis. It can affect joints, the spine, fingers and toes, tendons, skin, and nails. Joint symptoms can sometimes begin before obvious psoriasis appears.

Usual care: rheumatology care, immune-modifying treatment, exercise, and treatment of associated skin disease.

Crystal Arthritis

Gout

Gout is caused by uric acid crystals forming in and around a joint. A flare often starts suddenly with severe pain, redness, warmth, and swelling.

Usual care: medicine for the acute flare and, when needed, long-term treatment to lower uric acid.

Uric acid is not the only crystal that can cause arthritis. Calcium pyrophosphate deposition disease, sometimes called pseudogout, can also cause sudden pain and swelling and may resemble gout or infection.

Inflammatory Spine Disease

Axial Spondyloarthritis

This condition mainly affects the spine and the joints connecting the spine to the pelvis. Pain may be worse after rest, improve with movement, and come with prolonged morning stiffness.

Usual care: rheumatology evaluation, exercise, physical therapy, and anti-inflammatory or immune-targeted medicines when appropriate.

Needs Urgent Evaluation

Infectious Arthritis

An infection inside a joint can cause rapid pain, warmth, swelling, fever, or an inability to use the joint. It can resemble gout or another inflammatory flare.

Usual care: urgent joint-fluid testing, drainage, and antimicrobial treatment when infection is confirmed.

Where LDRT fits: This website discusses low-dose radiation therapy (LDRT) for osteoarthritis and degenerative joint pain. It is not a substitute for disease-modifying treatment of rheumatoid arthritis, psoriatic arthritis, or another autoimmune inflammatory condition.

How Doctors Tell the Types Apart

There is no single test that identifies every form of arthritis. Diagnosis usually comes from several pieces of information considered together.

Symptom patternWhich joints hurt, how symptoms began, morning stiffness, and whether movement helps or worsens the pain.

Physical examinationSwelling, warmth, motion, stability, tenderness, skin or nail changes, and tendon involvement.

ImagingX-rays may show structural changes; ultrasound or MRI can add detail. Imaging findings and pain levels don't always match up.

Blood testsThese can support certain diagnoses, but normal results do not rule out every inflammatory condition.

Joint fluidTesting fluid from a swollen joint may identify crystals, infection, bleeding, or another cause.

Who May Be Part of Your Care Team?

Primary Care Clinician

Often evaluates new symptoms, orders initial tests, treats common problems, and coordinates referrals.

Rheumatologist

Specializes in autoimmune, inflammatory, and crystal arthritis, including rheumatoid arthritis, psoriatic arthritis, gout, and axial spondyloarthritis.

Orthopedic Clinician

Evaluates injuries, structural joint damage, advanced osteoarthritis, and whether surgery may be appropriate.

Physical or Occupational Therapist

Helps with strength, mobility, balance, joint protection, assistive devices, and adapting daily activities.

Pain Specialist

May help when persistent pain has several causes or remains difficult to manage.

Radiation Oncologist

Evaluates whether LDRT may be a reasonable option for selected patients with osteoarthritis or degenerative musculoskeletal pain.

Living With Arthritis

Keep Moving

Long periods of inactivity can add to stiffness and weakness. Walking, cycling, swimming, water exercise, tai chi, and gradual strengthening are joint-friendly options for many people.

Build Strength Gradually

Stronger muscles can help support a painful joint. Start slowly and ask a clinician or physical therapist for guidance when pain, balance, or other health conditions limit activity.

Use Pacing, Not Prolonged Rest

Break demanding tasks into smaller steps, alternate heavier and lighter activities, and take short rests before pain becomes overwhelming.

Reduce Joint Strain

Supportive footwear, a correctly fitted cane, braces, splints, raised seats, and simple household tools can make daily activities easier.

Heat and Cold

Heat may ease stiffness and relax muscles. Cold may help short-term pain or swelling after activity. Protect the skin and avoid extreme temperatures.

Sleep and Mood Matter

Pain can disrupt sleep, and poor sleep can make pain harder to manage. Ongoing pain can also affect mood, concentration, work, and relationships. These concerns belong in the treatment conversation.

Symptoms That Should Not Wait

Seek urgent, often same-day medical care for a suddenly hot, red, or very swollen joint; fever or feeling very ill with joint symptoms; inability to bear weight after an injury; a new deformity; sudden weakness or numbness; loss of bowel or bladder control with severe back symptoms; or eye pain, redness, and light sensitivity in someone with inflammatory arthritis.

Sources: NIAMS arthritis overview, NIAMS osteoarthritis guidance, NIAMS rheumatoid arthritis guidance, and CDC arthritis basics.