When a joint becomes stiff, swollen, or painful, the immediate assumption is often “arthritis.” But arthritis isn’t a single disease. It is a broad umbrella term encompassing over 100 distinct conditions that affect the joints, tissues around the joint, and other connective tissues.
To understand arthritis, you have to look at the joint itself—the junction where two bones meet, cushioned by cartilage and lubricated by synovial fluid.
Explore this interactive breakdown of joint anatomy to see how ligaments, cartilage, and lubricating fluids change over time, leading to the friction and stiffness that characterise joint disease:
The Cause and Effect of Arthritis
Because there are dozens of arthritis variations, there is no single root cause. The pathology depends entirely on which type of arthritis a person has. Broadly, the causes fall into three main categories:
- Mechanical Wear and Tear: Over decades of use, the smooth cartilage cushioning the ends of bones wears down. This process is accelerated by joint injuries, obesity (which adds physical stress to weight-bearing joints), and genetics.
- Autoimmune Dysfunction: In some individuals, the immune system misidentifies healthy joint tissue (specifically the synovial membrane lining the joint) as a foreign invader and attacks it, triggering aggressive inflammation.
- Metabolic Accumulation: The body can overproduce or fail to clear certain waste products, such as uric acid. These substances crystallise inside the joint cavity, acting like microscopic shards of glass.
The Ripple Effect on the Body
The most immediate effect of arthritis is localised joint degradation. As cartilage breaks down, bones may begin to grind directly against one another. To compensate for the loss of stability, the body often remodels the bone, creating painful outgrowths called bone spurs (osteophytes). This leads to chronic pain, visible swelling, morning stiffness, and a severe reduction in mobility.
However, inflammatory forms of arthritis have systemic effects. Because the immune system is in overdrive, the effects aren’t limited to the joints. Patients frequently experience severe fatigue, low-grade fevers, and, in advanced cases, inflammatory damage to the heart, lungs, eyes, and blood vessels.
To see how drastically the effects vary by type, look at the difference between the structural damage of mechanical wear (Osteoarthritis) versus an inflammatory immune attack (Rheumatoid Arthritis):
The Core Varieties of Arthritis
While there are over 100 types, the vast majority of diagnoses fall into one of these primary categories.
Osteoarthritis (OA)
Often called “wear-and-tear” arthritis, OA is the most common joint disorder in the world. It is a degenerative condition where the protective articular cartilage slowly wears away over time. It most frequently strikes weight-bearing joints like the knees, hips, and lower spine, as well as the hands. Symptoms develop slowly over the ears, with pain worsening during movement and improving with rest.
Rheumatoid Arthritis (RA)
RA is an autoimmune and inflammatory disease. The immune system attacks the synovium—the membrane that encloses the joint. This causes the lining to thicken and swell, eventually destroying the cartilage and bone within the joint. Unlike OA, RA usually affects joints symmetrically (e.g., both wrists or both knees) and is characterised by prolonged morning stiffness lasting more than an hour.
Gout
Gout is an intensely painful metabolic form of arthritis. It occurs when high levels of uric acid in the blood lead to the formation of urate crystals in a joint—most notoriously the big toe, though it can strike ankles and knees. Gout attacks are sudden, severe, and episodic, often waking people up in the middle of the night with a joint that is red, hot, and excruciatingly sensitive to even the lightest touch.
Psoriatic Arthritis (PsA)
This inflammatory arthritis affects some people who have psoriasis, a condition that features red patches of skin topped with silvery scales. In PsA, the immune system attacks both the skin and the joints. A hallmark symptom is “sausage-like” swelling in the fingers and toes (dactylitis), along with changes to the fingernails, such as pitting or separation from the nail bed.
Ankylosing Spondylitis (AS)
AS is an inflammatory arthritis that primarily targets the spine. It causes severe inflammation of the vertebrae that can eventually lead to chronic pain and discomfort. In advanced cases, the inflammation causes new bone formation, which can cause sections of the spine to fuse together in a fixed, immobile position.