Aetiology

Septic arthritis is caused by the pathogenic inoculation of micro-organisms into the joint, either directly or by the haematogenous route. The predominant causative organisms of septic arthritis are staphylococci or streptococci.[2][3][4][5][6][7] These organisms account for 91% of cases.[4]

Risk factors for the development of joint sepsis include:

  • Pre-existing joint disease (e.g., rheumatoid arthritis or osteoarthritis)[3][8][9][10]

  • Joint prostheses[8][9]

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

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

  • HIV infection[9][11]

  • Alcohol use disorder[10]

  • Diabetes[8][9][10][12]

  • Previous intra-articular corticosteroid injection[13]

  • Recent joint surgery[8][9][12]

  • The presence of other infections including skin infections and cutaneous ulcers[2][3][8][9][10]

  • Exposure to ticks (may indicate arthritis associated with Lyme disease).[14]

In sexually active patients, gonococcal arthritis may be suspected. In older and immunocompromised people, gram-negative organisms are more common than among young people, although staphylococci and streptococci still predominate. Anaerobic organisms rarely cause septic arthritis except in the case of penetrating trauma.[15]

Community-associated MRSA is becoming more common in many parts of the world and should be suspected in patients recently discharged from hospital, nursing home residents, those with leg ulceration, and those with indwelling urinary catheters.

Tuberculous arthritis should be suspected in immunocompromised people and in patients who originate from areas where tuberculosis is prevalent.

Pathophysiology

Following pathogenic inoculation into the joint, the mechanisms by which joint sepsis subsequently develops are as yet not fully understood. Studies in experimental mouse models have revealed a complex array of bacterial virulence factors, as well as immunological host responses, which determine the development of disease. This multiplicity of components in disease pathogenesis may explain why antibiotics alone are not always sufficient to treat joint sepsis successfully.[1]

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