Arthritis Types at a Glance: A Reference Guide to Key Terms and Definitions

How to Use This Reference Guide

Arthritis is not a single disease — it is an umbrella term for more than 100 conditions that affect joints, surrounding tissues, and sometimes other organ systems. Because different types have different causes, patterns, and progression paths, knowing which form you or a loved one may be dealing with is an important first step toward informed care.

This guide is designed as a quick lookup resource. Each entry defines the condition, identifies which joints are typically involved, and highlights distinguishing features that set it apart from other types. For a deeper narrative overview, see our plain-language guide to major arthritis types.

This article is for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific symptoms and condition.

Core Arthritis Types: Definitions and Key Features

The entries below cover the most widely recognised forms of arthritis. Understanding their defining characteristics can help you recognise patterns and have more productive conversations with your doctor.

Osteoarthritis (OA)

What it is: The most common form, caused by the gradual breakdown of cartilage — the protective tissue at the ends of bones — leading to bone-on-bone friction, pain, and stiffness.

Joints commonly affected: Knees, hips, hands (especially finger joints), and spine.

Distinguishing feature: Symptoms typically worsen with activity and improve with rest; onset is usually gradual and age-related.

Rheumatoid Arthritis (RA)

What it is: An autoimmune disease in which the immune system mistakenly attacks the synovial lining of joints, causing chronic inflammation, pain, and eventual joint damage.

Joints commonly affected: Small joints of the hands and feet, wrists, and knees — often symmetrically (both sides of the body at once).

Distinguishing feature: Morning stiffness lasting more than one hour is a hallmark sign. RA can also affect non-joint tissues such as the lungs and eyes. See how OA and RA compare in depth.

Psoriatic Arthritis (PsA)

What it is: An inflammatory arthritis associated with psoriasis, a skin condition causing scaly patches. The immune system drives inflammation in both skin and joints.

Joints commonly affected: Fingers, toes, spine, and the joints where tendons attach to bone (entheses).

Distinguishing feature: "Sausage-like" swelling of entire fingers or toes (dactylitis) and nail changes (pitting, discolouration) are characteristic.

Gout

What it is: A form of crystal arthritis caused by the accumulation of uric acid crystals in joint fluid, triggering sudden, severe inflammatory attacks.

Joints commonly affected: The big toe is the classic site; ankles, knees, and wrists can also be affected.

Distinguishing feature: Attacks often start abruptly, frequently at night, with intense redness, warmth, and swelling. Compare gout with pseudogout to understand the differences between crystal arthritis types.

Pseudogout (Calcium Pyrophosphate Deposition Disease)

What it is: Similar to gout in mechanism but caused by calcium pyrophosphate crystals rather than uric acid crystals depositing in joint cartilage and fluid.

Joints commonly affected: Knees most often; wrists, ankles, and other large joints can be involved.

Distinguishing feature: Tends to affect older adults; crystals are visible on imaging as calcifications within cartilage (chondrocalcinosis).

Ankylosing Spondylitis (AS)

What it is: A chronic inflammatory condition primarily affecting the spine and sacroiliac joints (where the spine meets the pelvis), belonging to a broader family called spondyloarthritis.

Joints commonly affected: Lower back, sacroiliac joints, and sometimes hips, shoulders, and peripheral joints.

Distinguishing feature: Inflammatory back pain that improves with movement but worsens with prolonged rest; in advanced cases, vertebrae can fuse.

Juvenile Idiopathic Arthritis (JIA)

What it is: The most common form of persistent arthritis in children and adolescents, encompassing several subtypes with varying patterns of joint involvement and systemic features.

Joints commonly affected: Varies by subtype — can include knees, wrists, small hand joints, and spine.

Distinguishing feature: Onset before age 16; some subtypes carry a risk of eye inflammation (uveitis) with no obvious symptoms. Learn more about JIA subtypes and family guidance.

Lupus-Related Arthritis

What it is: Joint inflammation occurring as part of systemic lupus erythematosus (SLE), a wide-ranging autoimmune disease that can affect multiple organ systems.

Joints commonly affected: Small joints of the hands, wrists, and knees — often migratory (moving between joints).

Distinguishing feature: Joint symptoms appear alongside systemic signs such as fatigue, skin rashes (including a butterfly-shaped facial rash), and kidney or other organ involvement.

For a broader discussion of how inflammation separates certain types from others, explore inflammatory vs. non-inflammatory arthritis.

Next Steps: Using This Information Wisely

Recognising terms and patterns is a useful starting point, but a confirmed diagnosis always requires a thorough clinical evaluation — including physical examination, blood tests, and often imaging. No online reference can replace that process.

If you are managing a diagnosed condition, joint health habits — including movement, diet, and posture practices — are an important complement to medical treatment. For a comprehensive look at protecting joint function over time, see Protecting Your Joints for the Long Haul. Practical strategies for day-to-day symptom management are covered in Managing Joint Pain.

This article is for general informational and educational purposes only and does not constitute medical advice. If you have questions about your symptoms, diagnosis, or treatment, please consult a qualified healthcare professional.