10Osteoarthritis (OA) refers to a progressive, degenerative disease of the joint with only low grade inflammation which is accompanied by varying degrees of functional limitation, pain and reduced quality of life. It is by far the most common form of arthritis and one of the leading causes of pain and disability worldwide. Any synovial joint can develop osteoarthritis but knees, hips and small hand joints are the peripheral sites most commonly affected. Invariably the onset is insidious with intermittent exacerbations of mild to moderate aching pain, stiffness and swelling of the affected joint. Stiffness typically occurs at rest, particularly first thing in the morning and gradually eases with activity. Environmental changes such as cold and lowered barometric pressures may aggravate the affected joint. There is a poor correlation between the extent of radiological changes and clinical signs and symptoms.

Osteoarthritis is a metabolically active, dynamic process that involves all joint tissues (cartilage, bone, synovium/capsule, ligaments and muscle) showing increased cell activity and new tissue production. Key pathological changes are characterised by a discrete sequence of individual histological events that eventually lead to cartilage destruction and secondary alterations in the related tissues, including localised loss of articular (hyaline) cartilage and remodelling of adjacent bone with new bone formation (osteophyte) at the joint margins. This combination of tissue loss and new tissue proliferation supports the view of osteoarthritis as a repair process of synovial joints and represents a compensation for the initial trauma, resulting in a structurally altered, but occasionally, symptom-free joint. In some joints however, either because of overwhelming insult or compromised repair potential, the osteoarthritic process cannot compensate, resulting in continuing tissue damage and eventual presentation with symptomatic osteoarthritis or ‘joint failure’.