Osteoarthritis is a joint disease in which tissues change and break down over time. The hip and knee are among the joints it commonly affects. Although a worn joint is a familiar description, NIAMS explains that osteoarthritis involves changes within joint tissues rather than simple wear from use. It can affect people very differently, from relatively mild symptoms to pain and limitations in everyday activities. NIAMS explains osteoarthritis.
What changes inside the joint
Articular cartilage is the firm, smooth tissue over the ends of bones where they meet. It helps the surfaces glide during movement. MedlinePlus describes cartilage breakdown as a process that can leave fragments and allow bone surfaces to rub, contributing to pain, swelling and stiffness. The surrounding muscles and ligaments can also become weaker or stiffer. The joint and disc anatomy page explains the tissues behind these terms. MedlinePlus describes cartilage changes.
The bone can change as well. NIAMS describes changes in joint shape and small growths at the edges of the joint, called bone spurs. The lining of the joint and its supporting tissues can be involved, so osteoarthritis is not only a change in the surface covering. These structural changes help explain the vocabulary used in a report, but the effect on daily life remains part of the clinical assessment. NIAMS describes bone and joint changes.
A review of cartilage biology describes chondrocytes, the specialized cells within cartilage, maintaining the material around them. It reports that aging reduces their ability to maintain the tissue and increases the risk of changes at the cartilage surface. This is a biological explanation of part of the process. It does not establish how quickly a particular hip or knee will change or what operation might be appropriate. The cartilage review describes this process.
Who can develop osteoarthritis
Osteoarthritis becomes more common with age, but younger adults can develop it too. NIAMS identifies joint injury, unusual joint structure and inherited cartilage problems among reasons it may occur earlier. Other factors associated with the condition include a family history, repeated joint movements, and overweight or obesity. These are factors that contribute to risk; they do not identify a single cause for every person’s joint problem. NIAMS lists contributing factors.
How a hip or knee may feel
The common symptoms include pain with joint use, stiffness after rest, swelling and a reduced ability to move the joint. Symptoms can begin gradually. NIAMS describes hip pain in the groin, inner thigh or buttock, and notes that hip pain can spread toward the knee. With knee osteoarthritis, grinding sensations and a feeling that the knee may give way can occur as supporting tissues weaken. NIAMS describes hip and knee symptoms.
Everyday effects matter alongside the name of the condition. NIAMS describes difficulty with steps, getting into or out of a chair, and walking. Pain can also interfere with sleep and leave a person tired. The pattern differs between people. MedlinePlus notes that physical changes can appear on an X-ray or examination even when symptoms are absent, so an image alone does not describe the whole experience. MedlinePlus notes that symptoms and images can differ. NIAMS describes effects on daily life.
How clinicians assess the joint
NIAMS says there is no single test for osteoarthritis. Assessment may include a medical and family history, a physical examination, and images. The examination considers general health as well as the painful joint. X-rays may show a reduced joint space, bone changes and bone spurs, although early damage may not appear. Magnetic resonance imaging, called MRI, can show soft tissues in and around the joint. NIAMS explains the assessment.
Some tests look for other explanations for joint pain. NIAMS describes blood tests to rule out other causes and joint-fluid samples to look for problems such as infection. MedlinePlus similarly explains that blood tests can help identify alternative conditions rather than establish osteoarthritis itself. A discussion of what a test is intended to clarify can make the difference between these purposes easier to understand. NIAMS explains why other tests may be used.
How agencies describe treatment categories
NIAMS describes treatment as beginning with learning about the condition, exercise planned with a clinician, and weight management where relevant. It also discusses professionally fitted supports and medicines for symptoms. These are categories within an individualized plan rather than instructions for a reader to begin a particular activity or medicine. A physical therapist may be involved in joint function, and an orthopedic surgeon specializes in bone and joint treatment and surgery. NIAMS describes treatment planning.
The medicine categories listed by NIAMS include pain relievers, anti-inflammatory medicines, preparations applied to the skin and corticosteroid injections, which reduce inflammation. The choice and suitability of these approaches belong to the person’s clinical care. NICE’s osteoarthritis guidance covers diagnosis, information, management without surgery, medicines, follow-up and referral for joint replacement; it states that decisions must account for individual needs, preferences and circumstances. NICE describes the scope of its guidance. NIAMS describes medicine categories.
Other causes of joint damage
Rheumatoid arthritis is a different disease: the immune system, which normally protects the body, attacks its own tissues. NIAMS describes ongoing inflammation of the joint lining that can damage cartilage and bone. Pain and swelling can occur with both conditions, but their underlying processes differ. The distinction is one reason clinicians consider the history and other possible diagnoses when assessing a painful joint. NIAMS explains rheumatoid arthritis.
Osteonecrosis means damage and death of bone tissue after its blood supply is disrupted. NIAMS describes the hip as a common site and notes that disease near a joint can lead to bone breakdown and arthritis. It is another possible route to joint damage, rather than another name for osteoarthritis. The diagnosis matters to the discussion of what the joint needs. NIAMS explains osteonecrosis.
When replacement becomes part of the conversation
NIAMS describes surgery as a possibility when other treatments are not helping and joint damage is extensive. Its discussion includes pain, the effect on daily life, disability and occupation among the considerations. Replacement removes damaged parts and uses artificial components. The hip replacement page and knee replacement page explain the operations; neither the diagnosis nor a scan result alone supplies a decision for an individual person. NIAMS describes the surgery discussion.