Characteristics

• Chronic joint disorder characterised by a progressive loss of articular cartilage and marginal new bone formation.

• Classified as primary in which no cause is found, or secondary. Usually a combination of both primary and secondary factors is involved.

• Generally a disease of the elderly but seen in younger patients with articular cartilage damage or where abnormal stresses are involved.

• Characterised by progressive cartilage loss, marginal osteophyte formation, subarticular cysts, bone sclerosis and capsular fibrosis.

Clinical features

• Commoner in weight-bearing joints (hip, knee and spine) than in others (glenohumeral). Interphalangeal involvement is more common in women. Previous injury to the joint can predispose.

• Family history – the known genetic trends may eventually explain OA.

• Pain is common and may be referred from an adjacent joint. Typically, worse in the morning or with immobilisation and aggravated by exertion.

• Stiffness common after inactivity, but may be constant with disease progression.

• Swelling from joint effusion, capsular thickening and/or osteophyte formation.

• Loss of function is generally a late feature. Look for muscle wasting as an indicator.

• ‘Joint failure’ – including muscle, bone and cartilage.

Radiographic features

• Good quality multi-view X-rays form the main imaging modality.

• Ensure that films are taken with the appropriate loading, e.g. weight-bearing.

• Look for loss of joint space, subchondral cysts, marginal osteophytes and bony sclerosis. Bone density is generally preserved.

• CT can be useful to assess if cortical bone is involved. May reveal loose bodies not evident on plain radiography.

• MRI is the modality of choice to identify cartilage loss. Effusions and cysts are better demonstrated with MRI.

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