infectious arthritis (septic arthritis)

Introduction

Generally, inflammation of a joint caused by bacterial invasion.

Etiology

• Staphylococcus aureus
  • most common cause of septic arthritis
  • affects native & prosthetic joints
  • medical emergency
• Neisseria gonorrhoeae
  • common cause in sexually-active young adults
  • 3 distinct syndromes
    • arthritis-dermatitis syndrome
    • arthritis-urogenital syndrome
    • purulent gonococcal arthritis
• Neisseria meningitidis
  • may produce an arthritis-dermatitis syndrome indistinguishable from Neisseria gonorrhoeae
• coagulase negative Staphylococcus
• Streptococcus species
  • Streptococcus pneumoniae
  • Streptococcus pyogenes
  • Streptococcus agalactiae
• gram negative bacilli
  • Escherichia coli
  • Salmonella, especially osteomyelitis
  • Pseudomonas
  • Haemophilus influenzae
  • more common in elderly, immunosuppressed, post-op, injection drug users, or patients with recent trauma, GI infection or with intravenous catheters
• Brucella preferentially involves spine
• tuberculosis
  • preferentially involves spine (spondylitis, osteomyelitis)
  • may also involve hip or knee
  • concurrent pulmonary tuberculosis in a minority of patients
• Mycobacterium marinum
• Borrelia burgdorferi (Lyme disease)
  • late-stage manifestation
  • generally monoarticular, most commonly involves knee
• viral arthritis:
  • rubella
  • parvovirus B19
  • hepatitis B & hepatitis C
  • HIV
• fungus (subacute monoarthritis in a patient with systemic mycosis)
  • Sporothrix schenckii
  • Histoplasma
  • Crytococcus
  • Blastomyces
• prosthetic joint (prosthetic joint infection) or recent joint surgery
• general risk factors for infectious arthritis
  • sources of infection
    • wounds
    • skin infection
    • pneumonia
    • urinary tract infection
  • injection drug use associated with subacute septic arthritis
    • septic sacroiliitis, sternoclavicular joint & pubic symphysis involvement
    • gram-negative bacilli: coverage for Pseudomonas
  • pre-existing arthritis or joint damage
    • rheumatoid arthritis
  • intra-articular glucocorticoid injection
  • age > 80 or very young children
  • low socioeconomic status
  • alcoholism
  • diabetes mellitus
  • end-stage renal disease
  • immunosuppression
  • sickle cell disease
  • underlying malignancy

Pathology

• hematogenous spread from another primary site of infection
• contiguous spread to joint from soft tissue or adjacent bone

Clinical manifestations

• acute onset monoarthritis (< 48 hours)
  • worsening of chronic inflammatory arthritis in a single joint
  • previously damaged joints at increased risk
  • onset generally over a few days
• constitutional symptoms, fever, shaking chills uncommon
• affected joint may be warm, erythematous, swollen & painful with limited joint mobility
• loss of active & passive range of motion
  • pain on passive range of motion in the absence of trauma
• pain & swelling less in elderly & in patients receiving glucocorticoids
• joints commonly affected
  • knee is involved in 1/2 of the cases
  • hips
  • shoulders
  • wrists
  • ankles
  • elbows
  • spine - involves vertebral body & adjacent intervertebral disk space
  • in drug abusers (Staphylococcus aureus, Pseudomonas)
    • sternoclavicular joint & acromioclavicular joint
    • sacroiliac joint
• migratory arthragia, tenosynovitis (wrist or ankle) & dermatitis (vesiculopustular) = disseminated gonococcal infection
  • disseminated gonococcal infection may also present as a purulent monoarthritis or oligoarthritis
• overlying skin infection in a patient who has recently undergone arthroplasty suggests prosthetic joint infection

Diagnostic criteria

• acute monoarticular arthritis.
• positive gram stain/culture from synovial fluid (exception Neisseria gonorrhoeae)

Laboratory

• synovial fluid cell count with differential
  • appearance: yellow, purulent, or bloody
  • 50,000-200,000 WBC/mm3 with > 90% neutrophils
    • cell count for gonococcal arthritis lower than other types of infectious arthritis, as low as 14,000 WBC/mm3 with 85% neutrophils
  • RBCs present
• synovial fluid Gram stain, culture & sensitivity
  • gram stain negative in 20% of septic arthritis, especially common with gram-negative organisms
  • septic arthritis can cause release of calcium pyrophosphate crystals from cartilage
• serum glucose & synovial fluid glucose
  • synovial fluid glucose often < 50% fasting serum glucose
• "string test": normal synovial fluid when gently pushed from syringe will form a 5-10 cm "string". With infection, the "string" will be shorter
• polarized microscopy of joint fluid for crystals
  • septic arthritis can develop in patients with crystalline arthritis
  • crystals in synovial fluid does not exclude infection
• complete blood count (CBC) may show leukocytosis
• blood cultures (obtain specimens prior to empiric antibiotics)
• if disseminated gonococcal infection is suspected, also wound culture (skin pustule), urethral culture or cervical culture, rectal culture, throat culture
  • Neisseria gonorrhoeae DNA vs culture
  • synovial fluid cultures tend to be negative*
• CH50 assay screen for complement deficiency:
  • all patients with recurrent disseminated gonorrhea
  • family history of disseminated Neisseria infection
• see ARUP consult

* septic arthritis caused by N gonorrhoeae (vs disseminated gonococcal infection) is monoarticular or pauciarticular, & is more commonly associated with positive synovial fluid cultures & negative blood cultures

Diagnostic procedures

• arthrocentesis for synovial fluid
• synovial biopsy for tuberculous arthritis

Radiology

• plain films of joint (rarely helpful)
  • soft tissue swelling & distension of joint capsule early
  • joint destruction may be observed as a late manifestation
  • evidence of co-existing osteomyelitis may be present
• bone scan may be useful, but is non-specific
• magnetic resonance imaging (MRI)

Differential diagnosis

• rheumatoid arthritis monoarticular flare

Management

• joint aspiration & drainage daily from bacterial infection of native joint until fluid ceases to accumulate
• arthroscopic or open drainage may be necessary if joint fluid cannot be completely evacuated by aspiration
  • early orthopedic consultation recommended
  • multiple procedures may be necessary in 50% of patients especially patients with diabetes mellitus
• antibiotic therapy (after synovial fluid & blood collection)
  • determined by clinical condition & laboratory studies
  • empiric antibiotic therapy
    • no organisms seen on gram stain
      • vancomycin or linizolid + 3rd generation cephalosporin or cefepime or ceftazidime (Pseudomonas, IVDA)
      • narrow spectrum of antibiotic coverage based on culture & sensitivity
      • antibiotic coverage for 7-14 days even if cultures negative
      • vancomycin + ceftazidime if low risk for gonorrhea
    • gram positive cocci
      • always initiate therapy with coverage for MRSA
      • vancomycin or linizolid for MRSA; teicoplanin 2nd line
      • nafcillin or oxacillin +/- gentamicin for MSSA; cefazolin 2nd line
    • gram negative bacilli
      • ceftriaxone or cefotaxime; fluoroquinolone 2nd line
      • include ceftazidime + gentamicin, cefepime, or Zozyn if Pseudomonas - injection drug use
      • if gonococcal arthritis, treat for co-infection with Chlamydia (doxycycline or azithromycin)
    • suspect tuberculous arthritis or fungal arthritis if empiric antibacterial therapy is unsuccessful
  • duration of therapy:
    • 2 weeks or 3 weeks if post-Chlamydia arthritis
    • some patient may require 6 weeks or more of therapy
    • 2 weeks non-inferior to 4 weeks
  • oral antibiotics non-inferior to IV antibiorics
• amphotericin B, echinocandin or azole (itraconazole, fluconazole, voriconazole, posaconazole) for fungal arthritis
• standard 3-4 drug treat of tuberculosis for tuberculous arthritis
• acute viral arthritis is generally self-limiting & may be managed symptomatically
• surgery + antibiotics for infected prosthesis
  • removal of hardware is generally required
  • consult orthopedic surgery if prosthetic joint infection is suspected
• splinting of joint may provide symptomatic relief
• passive range of motion exercises once pain has diminished followed by active exercise to restore strength & joint mobility
• bony fusion may be required with severely damaged weight-bearing joints
• poor outcomes are common even with aggressive management
• glucocorticoids
  • persistent synovitis & effusion after cure of infection may respond to a single intra-articular glucocorticoid injection
  • document negative cultures after completion of antibiotics prior to glucocorticoid injection
  • administration of dexamethasone 0.2 mg/kg IV every 8 hours for 12 doses improved outcomes in children; 1st dose administered 15-20 minutes before 1st dose of parenteral antibiotics

More general terms

• arthritis
• infection (infectious disease)

More specific terms

• fungal arthritis
• HIV-associated arthritis
• infected prosthesis
• infectious arthritis ankle/foot
• infectious arthritis elbow
• infectious arthritis hand
• infectious arthritis hip
• infectious arthritis in the elderly
• infectious arthritis knee
• infectious arthritis shoulder
• infectious arthritis wrist
• tuberculous arthritis
• viral arthritis

Patient information

infectious arthritis (septic arthritis) patient information