Septic arthritis
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Background
Septic arthritis is infection of one or more joints, typically by bacteria, leading to inflammation of the synovium and accumulation of purulent material within the joint space.It most commonly occurs through haematogenous spread but may also result from direct inoculation (e.g. trauma, injection) or contiguous spread from adjacent infection. The most frequent causative organism in adults is Staphylococcus aureus. Prosthetic joint infections represent a distinct subgroup with higher risk and more complex management.
Risk Factors
- Older age and immunosuppression
- Underlying joint disease (e.g. rheumatoid arthritis, osteoarthritis) or previous joint damage
- Prosthetic joints or prior joint surgery/injection
- Skin infections, adjacent osteomyelitis, or intravenous drug use
Clinical Features
- Acute onset of a hot, swollen, painful joint with reduced range of motion
- Fever and systemic symptoms may be present but are not universal
- The knee is most commonly affected, followed by hip, shoulder, and elbow
- Prosthetic or indolent infections may present more gradually with subtle signs
Diagnosis and Investigations
- Joint aspiration (arthrocentesis) is essential in all suspected cases before antibiotics are started, synovial fluid should be sent for Gram stain, culture, cell count, and crystal analysis
- Blood cultures should be obtained concurrently
- Laboratory tests such as CRP, ESR, and WBC are usually elevated but nonspecific
- Plain radiographs may help exclude fractures or chronic bone changes
- Ultrasound or MRI can detect joint effusions, guide aspiration, or assess soft tissue extension
Key points:
- most common organism overall is Staphylococcus aureus
- in young adults who are sexually active Neisseria gonorrhoeae should also be considered
- needle aspiration should be used to decompress the joint
- IV antibiotics which cover Gram-positive cocci are indicated. The BNF currently recommends flucloxacillin (or clindamycin if penicillin allergic) as first line. Alternate antibiotics used if gonococcal arthritis or septic arthritis in prosthetic joint.
- antibiotic treatment is normally given for several weeks (BNF states 4-6 weeks)
- surgical drainage and lavage is a key part of management
Management
Empiric intravenous antibiotics should be started promptly after aspiration and adjusted according to culture results and sensitivities.
Joint drainage is mandatory, as antibiotics alone are insufficient; this may involve repeated needle aspiration, arthroscopic washout, or open surgical drainage
Duration of therapy is typically 4–6 weeks, beginning with intravenous antibiotics followed by an oral course
Supportive care includes analgesia, joint rest or splinting initially, and early physiotherapy once inflammation subsides
Prosthetic joint infection management may require prosthesis removal and staged reimplantation or long-term suppressive antibiotics depending on the case