OA General Principles

Osteoarthritis (OA) is the most common joint disease and a leading cause of musculoskeletal pain and disability, affecting the whole joint rather than simply wearing out the cartilage.

It most often affects the knees, hips, hands, spine and 1st metatarsophalangeal joint. Management centres on 3 core treatments: therapeutic exercise, weight management where needed, and information and support.

OA involves every tissue of the joint:

• •Cartilage: breakdown outpaces repair, so the surface fibrillates and erodes
• •Subchondral bone: sclerosis, cysts and bone marrow lesions, which are linked with pain
• •Osteophytes at the joint margins, the most characteristic radiographic feature
• •Synovium: low-grade synovitis, contributing to pain, effusion and flares
• •Muscle: weakness and wasting, both a result of OA and a contributor to abnormal loading

Risk factors:

• •Non-modifiable: age (the strongest), female sex, genetics, previous joint injury and malalignment
• •Modifiable: overweight and obesity (the main modifiable factor, especially at the knee), inactivity, occupational loading and muscle weakness

Most OA is primary. Secondary OA has an identifiable cause: previous trauma (the usual cause at the ankle), inflammatory or crystal arthritis, haemochromatosis, developmental hip disease, avascular necrosis or a Charcot joint. OA in an atypical joint or in someone under 45 should prompt a search for one.

Generalised (nodal) OA affects the hands, knees and hips and is commoner in post-menopausal women.