History and exam

Key diagnostic factors

common

hot, swollen, painful, restricted joint

Regard a hot, swollen, acutely painful joint with restriction of movement as septic arthritis until proven otherwise.[10] Do so even in the absence of fever and irrespective of microbiology and blood test results.[10]

Pain and swelling are the most common symptoms in septic arthritis.[10]

  • If the affected joint is not weight-bearing, the patient with septic arthritis will be extremely reluctant to let you examine it.

Practical tip

Most patients with septic arthritis of a weight-bearing joint will not be able to walk.

The joint is often held in a position that maximises the joint space (fully extended knee; hip abducted, flexed, and externally rotated).

Intra-articular pathology is indicated by severe limitation of active and passive movement.

An intra-articular effusion may be present.[9][10]

acute presentation

Symptoms have usually been present for <2 weeks.[4][5][10]

Delays in presentation may occur with low-virulence organisms, tuberculosis, or prosthetic infections.[4][5][10]

Other diagnostic factors

common

fever

Not a reliable indicator of infection.[3][4][5][10]

  • Present in approximately 60% of cases.[10]

  • Sensitivities for septic arthritis of constitutional symptoms are:[10]

    • Fever 57%

    • Chills 27%

    • Rigors 19%.

large joint

The commonest reported site of isolated septic arthritis is the knee.[9][10] The hip, shoulder, ankle, elbow, and wrist are also common sites of joint infection.[9]

Infection of axial joints, such as the sternoclavicular or sacroiliac joint, is more common in patients with a history of intravenous drug misuse.[9]

The metatarsophalangeal joint of the great toe is the commonest joint to present as hot, swollen, and painful in primary care, but this presentation is unlikely to be caused by septic arthritis. This is almost always due to gout and can be diagnosed clinically without needle aspiration.

single joint

Most presentations are monoarticular, but up to 22% of patients with septic arthritis have oligoarticular or polyarticular disease.[10]

prosthetic joint

Always suspect joint infection if a joint prosthesis is present and symptomatic.[8]

  • Refer all patients with symptomatic prosthetic joints to orthopaedics.[22]

proportionality of symptoms

In patients with underlying joint disease (such as rheumatoid arthritis or osteoarthritis), suspect a septic joint if symptoms are out of proportion to disease activity elsewhere.[10]

Practical tip

Think about the possibility of septic arthritis in patients with an apparent monoarticular flare-up of rheumatoid arthritis.[8][23]

  • Immunosuppressive medications increase the risk of septic arthritis.[8]

  • Anti-tumour necrosis factor alpha may further increase the risk of infection.[8][23][35]

sexual activity

Usually with no other risk factors for septic arthritis, young and healthy patients may present with gonococcal septic arthritis.[10]

May present as either localised septic arthritis, or an arthritis-dermatitis syndrome characterised by malaise, polyarthralgias tenosynovitis, and dermatitis.[9]

erythema migrans

An initial history of erythema migrans, migratory joint pains, and, later, intermittent oligoarthritis usually involving the knee or other large joints may suggest Lyme arthritis.[14]

See the UK National Institute for Health and Care Excellence guideline on Lyme disease for further details. NICE: Lyme disease Opens in new window

risk factors

Screen for the following risk factors:[9][10]

  • Underlying joint disease

    • Osteoarthritis[9]

    • Rheumatoid arthritis[3][8][9][10]

  • Prosthetic joint[8][9]

  • Age >80 years[8][9]

  • Low socioeconomic status[4][10]

  • Immunosuppression

    • HIV[9][11]

    • Intravenous drug misuse[9][10][11]

    • Diabetes[8][9][10][12]

    • Alcohol misuse[10]

    • Immunosuppressive medication[3][10][11]

  • Contiguous spread

    • Ulcerated skin or skin infection[3][8][9][10]

      • Can lead to bacteraemia and subsequent seeding of infection in a joint

  • Haematogenous spread

    • Other causes of infection, such as a urinary tract infection or skin infection[3][9]

    • Intravenous drug misuse[9][10][11]

  • Iatrogenic

    • Previous intra-articular corticosteroid injection[8][9][10][12]

    • Recent joint surgery[8][9][12]

  • Exposure to ticks may indicate arthritis associated with Lyme disease. Note travel to or residence in:

    • Many parts of the US: Eastern states (mainly New England and the mid-Atlantic), Northern midwestern states (especially Wisconsin, Minnesota, and the Great Lakes region), and the West Coast (particularly northern California and, less commonly, Oregon and Washington)[32]

    • Grassy/wooded areas in the UK and the Highlands in Scotland[14]

    • Central Europe, especially Austria, Czech Republic, southern Germany, Switzerland, Slovakia, and Slovenia[33]

    • Some parts of Asia (Lyme disease is well established in China).[34]

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