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Introduction

The knee, which is a gliding hinge joint, is the largest synovial joint in the body. Its small area of contact of the bone ends at any one time makes it dependent on ligaments for its stability. Although this allows a much increased range of movement it does increase the susceptibility to injury, particularly from sporting activities. Finding the cause of a knee problem is one of the really difficult and challenging features of practice. It is useful to remember that peripheral pain receptors respond to a variety of stimuli. These include inflammation due either to inflammatory disorders or chemical irritation such as crystal synovitis, traction pain (e.g. trapped meniscus stretching the capsule), tension on the synovium capsule (e.g. effusion or haemarthrosis), and impact loading of the subchondral bone.

Disorders of the knee account for about one presentation per 50 patients per year.1

The commoner presenting symptoms in order of frequency are pain, stiffness, swelling, clicking and locking.1

The age of presentation of a painful knee has varied significance as many conditions are age-related.

Excessive strains across the knee, such as a valgus-producing force, are more likely to cause ligament injuries, while twisting injuries tend to cause meniscal tears.

A ruptured anterior cruciate ligament (ACL) is a commonly missed injury of the knee.2 It should be suspected with a history of either a valgus strain or a sudden pivoting of the knee, often associated with a cracking or popping sensation. It is often associated with the rapid onset of haemarthrosis or inability to walk or weight-bear.

A rapid onset of painful knee swelling (minutes to 1–4 hours) after injury indicates blood in the joint—haemarthrosis.

Swelling over 1–2 days after injury indicates synovial fluid—traumatic synovitis.

Any collateral ligament repair should be undertaken early but, if associated with ACL injuries, early surgery may result in knee stiffness. Thus, surgery is often delayed. With isolated ACL ruptures, early reconstruction is appropriate in the high-performance athlete; otherwise, delayed reconstruction is appropriate if there is clinical instability.3

Acute spontaneous inflammation of the knee may be part of a systemic condition such as rheumatoid arthritis, rheumatic fever, gout, pseudogout (chondrocalcinosis), a spondyloarthropathy (psoriasis, ankylosing spondylitis, reactive arthritis, bowel inflammation), Lyme disease and sarcoidosis.