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What Is Osteoarthritis?
Osteoarthritis is a chronic joint disease in which tissue breaks down and is remodeled over time, causing the entire joint to gradually change. It is therefore not just “wear and tear,” but a biological process in which the body’s ability to repair itself is no longer sufficient.
Osteoarthritis can affect several joints, but it is most common in the knees, hips, fingers, and spine. The disease often develops slowly, and symptoms vary from person to person.
A Healthy Joint vs. a Joint with Osteoarthritis
In a normal joint, the ends of the bones are covered with a layer of articular cartilage, which acts as a shock absorber and reduces friction during movement. The joint is surrounded by a joint capsule containing synovial fluid that lubricates and nourishes the cartilage. In osteoarthritis, the interaction between these structures is disrupted. The changes do not occur in the cartilage alone, but affect the entire joint.
The Cartilage Gradually Thins
In osteoarthritis, cartilage breaks down faster than the body can repair it. It becomes thinner, may become uneven, and can sometimes crack. When the cartilage no longer provides adequate protection, pressure on the underlying bone increases. This makes the joint more sensitive and can cause pain.
Changes in the Bone and Bone Spurs
When the cartilage does not function properly, the body attempts to adapt. The bone beneath the cartilage can become harder and thicker. At the edges of the joint, small bony outgrowths called osteophytes may form. These bone spurs are the body’s way of making the joint more stable, but they can also cause stiffness and limit mobility. The load within the joint is redistributed, which may worsen symptoms.
Joint Irritation and Increased Synovial Fluid
In osteoarthritis, mild irritation often develops in the joint. The synovial membrane, where synovial fluid is produced, can become irritated. This can lead to an increased amount of synovial fluid, causing the joint to feel swollen and tight. This irritation contributes to pain and stiffness, especially in the morning or after sitting still for a long period.
What Causes Pain in Osteoarthritis?
The cartilage itself does not contain nerves and cannot cause pain. Instead, the pain comes from other parts of the joint, such as the bone beneath the cartilage, the joint capsule, and the irritated synovial membrane. The muscles around the joint can also become tense and tender.
The pain is often most intense when the joint is under load, for example when walking or standing up. Early on, it usually feels better at rest. Stiffness is most noticeable after sitting still and typically improves once the body starts moving.
Difference Between Osteoarthritis and Normal Aging
The body and joints change with age. Cartilage can become slightly thinner over time without causing symptoms. In osteoarthritis, however, the changes are more pronounced. Cartilage breaks down more rapidly, bone spurs may form, and pain and stiffness can affect daily life.
Common Symptoms of Osteoarthritis
Osteoarthritis often develops gradually. Common symptoms include pain when the joint is under load, stiffness after rest, reduced mobility, and sometimes clicking or grinding sounds during movement. The joint may also swell periodically, especially after high levels of activity.
When Should You Seek Medical Care?
Contact a healthcare provider if:
- You have joint pain that does not go away and makes daily life difficult.
- The joint becomes clearly swollen, warm, or very painful.
- You develop a fever in combination with joint pain.
Examinations and Diagnosis
The diagnosis of osteoarthritis is made through a clinical examination in which the doctor listens to your symptoms and examines the joint. They assess how you move, where it hurts, and whether the joint is swollen. In many cases, this is sufficient to make a diagnosis.
In some cases, imaging may help confirm the diagnosis. If a more detailed assessment is needed, X-ray, magnetic resonance imaging (MRI), or ultrasound may be used. These methods can help show early joint changes or support follow-up of symptoms.
Related Conditions
Osteoarthritis should not be confused with arthritis. Osteoarthritis is primarily caused by cartilage breakdown and gradual structural changes in the joint. Arthritis is an inflammatory disease in which the immune system attacks the joint. These are two different conditions that are treated in different ways.
