The classical presentation of infectious arthritis is acute onset of pain, warmth and swelling of a single joint.
The range of motion is usually decreased.
The knee is the most commonly affected but any joint may be involved.
Fever and chills may be present.
More than 1 joint may be involved in patients with pre-existing joint disease, other inflammatory conditions or severe sepsis, and in some patients infected with certain pathogens eg N gonorrheae, N meningitidis and Salmonella spp.
Infectious arthritis must always be a part of the differential diagnosis in a patient with an acute monoarthritis. 


  • Monitor patient for improvement of clinical signs & symptoms
  • Levels of ESR & CRP may be used to evaluate response to treatment
  • Specialist referral should be considered in patients w/ features of sepsis for possible drainage & parenteral antibiotic therapy
  • Continue empiric treatment if patient is improving & cultures are negative
  • Serial analysis of the synovial fluid should show a decreasing WBC count & should revert to the sterile state w/ treatment
  • If a patient does not improve w/ appropriate treatment, consider:
    • Revision of antibiotic therapy
    • Open drainage of joint, biopsy & repeat culture, washout or debridement may be required
    • Repeating tests to uncover a possible non-infectious cause of arthritis
    • Consider specialist referral
  • Outpatient parenteral antibiotic therapy may be considered in patients in whom it is not feasible to complete treatment w/ oral antibiotics
    • A functioning outpatient parenteral antimicrobial therapy (OPAT) program should have a complete & qualified health care team, efficient means of communication, guidelines for follow-up, testing & other interventions, written policies & procedures & outcomes monitoring
    • A candidate for inclusion in an OPAT program should be willing to participate in the program & should have a home environment that is sufficient to support care


  • Family history of gout
  • Sexual history including history of N gonorrhoeae infection
  • Travel & occupational history
  • Diet & alcohol consumption

Physical Examination

  • Patients most often present w/ a red, warm, swollen & very tender joint
    • Affected joint may also present w/ effusion & severe restriction of movement
  • Exam should focus on the involved & contralateral joint & surrounding area including the skin & soft tissue
    • A general exam should be performed to search for other joint involvement, look for systemic manifestations of disease & seek extra-articular sources of infection
    • Gonococcal infections may manifest w/ fever, multiple painless macules & papules on the arms, legs or trunk, & tenosynovitis
    • Patients w/ rheumatoid arthritis may present exacerbation of inflammation in one or more joints
  • In children w/ infectious arthritis of the hip, the hip may be kept flexed & externally rotated, w/ severe pain on motion
  • Few physical signs may be found in patients w/ infectious arthritis of the spine, sacroiliac joints & hips
  • The absence of fever does not rule out infectious arthritis

Laboratory Tests

Synovial fluid exam 

  • Synovial fluid aspiration is the most important test for diagnosing infectious arthritis & should be done for all patients suspected of having infectious arthritis
  • Gram stain, culture, white blood cell (WBC) count w/ differential should be done
    • Gram stain is positive in only 60-80% of cases; a negative Gram stain &/or culture does not exclude the diagnosis of infectious arthritis
    • A WBC count of >50,000 cells/mm3 w/ neutrophil predominance is highly suggestive of bacterial arthritis
    • Synovial fluid glucose is usually decreased while protein & lactate dehydrogenase are usually increased in both inflammatory & infectious causes of arthritis
  • Routine polymerase chain reaction (PCR) is not recommended; may be useful in prosthetic joint infection to differentiate between septic & aseptic loosening & in culture-negative patients w/ similar presentation as reactive arthritis
  • Polarizing microscopy to evaluate crystals should be performed
  • Synovial biopsy is the most sensitive (95%) way to confirm a diagnosis of mycobacterial infectious arthritis

Blood culture

  • Should be obtained in all patients suspected of having infectious arthritis
  • Positive in 50% of cases

Complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP)

  • Used to determine presence of infection or inflammation; ESR & CRP are useful for monitoring treatment response
  • Leukocytosis is usually present (leukocyte count of 50,000-150,000 cells/mm3)
  • ESR is usually >20 mm/hour
  • CRP is usually raised; a normal CRP is a good negative predictor for infectious arthritis
  • Normal levels of ESR, CRP &/or WBC do not rule out infectious arthritis

Other laboratory tests

  • Blood urea nitrogen (BUN), creatinine & liver function tests should be taken to detect end-organ damage, a poor prognostic factor in infectious arthritis
  • Appropriate specimens from other sites (eg cervix, urethra & throat) should be taken in patients in whom genitourinary, respiratory or other infections are being considered


  • Plain x-rays of affected joints are not very helpful in diagnosing infectious arthritis but may act as a baseline to help exclude osteomyelitis or other abnormalities of the bone
    • X-rays done during early infection are usually normal but may show soft tissue swelling, displacement of the fat pad, or joint space widening secondary to localized edema
  • Magnetic resonance imaging (MRI) is a sensitive test for distinguishing infectious arthritis from osteomyelitis & demonstrates adjacent soft tissue edema & abscesses
  • Computed tomography (CT) scan is helpful in detecting effusions & inflammation in joints that are difficult to examine because of complex anatomy (eg hip & shoulder)
  • Ultrasonography may detect fluid in suspected infectious arthritis of the hip & may be used to perform an imaging-guided joint aspiration
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