- Clinical science
Septic (infectious) arthritis is a bacterial infection of the joint space. Contamination occurs either via the bloodstream, iatrogenically, or by local extension (e.g., penetrating trauma) and patients with damaged (e.g., patients with rheumatoid arthritis) or prosthetic joints have an increased risk. Patients usually present with an acutely swollen, painful joint, limited range of motion, and a fever. Suspected infectious arthritis requires prompt arthrocentesis for diagnosis. In addition to the immediate broad-spectrum antibiotic therapy, surgical drainage and debridement may be necessary to prevent cartilage destruction and sepsis.
Mechanism of infection
- Hematogenous spread (most common)
- Direct contamination
- Contiguous spread (e.g., septic bursitis, osteomyelitis)
- Risk factors
- Causative organisms
- Etiology 
- Usually prolonged, low-grade course
- Minimal swelling, with or without a sinus that drains pus
- Can present acutely (see “Clinical features” above)
- Conventional x-ray: loosening of the prosthesis, periosteal reactions
- For other diagnostic tests see “Diagnostics” below
In order to avoid infection, strict sterile techniques should be ensured in any procedure that involves penetration of the joint space.
- Uncommon condition that requires urgent treatment to avoid destruction of the joint
- Etiology: S. aureus and group A streptococcus account for the majority of cases
- Clinical findings
- For diagnostics and therapy, see respective sections below.
Bacterial coxitis is an orthopedic emergency!
Gonococcal arthritis is the most common form of arthritis in sexually active young adults! In a young, sexually active adult presenting with classic symptoms of septic arthritis, gonococcal infection must be ruled out!
- If septic arthritis is suspected, arthrocentesis should be conducted for synovial fluid analysis. Imaging (e.g., X-ray, MRI) may be indicated to assess potential underlying diseases or differential diagnoses.
Ultrasound-guided arthrocentesis: Definitive diagnosis requires detection of bacteria in the synovial fluid.
- To conduct , gram stain, and culture
- ↑ Synovial fluid WBC and dominance of polymorphonuclear (PMN) cells
- Fluid appears yellowish-green and turbid
- Synovial fluid culture and gram stain is positive in most patients with bacterial arthritis.
- Also alleviates pain by decreasing intraarticular pressure
- Laboratory tests
Imaging: to look for signs of underlying osteomyelitis and concurrent joint disease and rule out possible differential diagnoses (see “Differential diagnosis” below)
- Ultrasound: effusion, edema of the surrounding soft tissue, possible empyema
- X-ray: unremarkable early in the course of septic arthritis; osteolysis usually becomes visible after 2–3 weeks.
MRI or scintigraphy for early detection
- MRI provides early evidence of infectious involvement of the surrounding soft tissue
- Scintigraphy is used for detection or exclusion of polyarticular involvement
Differential diagnosis based on synovial fluid analysis findings
|Appearance||WBCs/μl (PMN %)||Glucose levels||Culture||Crystals|
|Normal synovial fluid|| || || || || |
|Noninflammatory arthritis|| || || || |
|Inflammatory|| || || || |
|Septic|| || || || || |
|Hemorrhagic|| || || || || |
Further differential diagnoses to consider
- Etiology: parvovirus B19, hepatitis B virus, hepatitis C virus, rubella virus, HIV
- Clinical findings
- History and clinical findings are the mainstay of establishing a diagnosis
- Serology: antibodies against the suspected virus
Synovial joint analysis: very variable (can be normal or inflammatory)
- Not routinely used since viral isolation is usually not successful
- For other diagnostic tests, see “Diagnostics” above
- Therapy: supportive treatment only (usually self-limited; see also learning cards on , , , and )
- Etiology: Histoplasma species, Sporothrix schenckii, Blastomyces species, Coccidioides species
- Clinical findings: very variable with acute and chronic courses, often with symptoms of disseminated infection (e.g., pulmonary symptoms)
- See “Overview of fungal infections” in the learning card for additional information
Acute onset, monoarticular arthritis
- Joint trauma
Acute or sub-acute onset polyarthritis
- See section on in learning card on
The differential diagnoses listed here are not exhaustive.
Empiric antibiotic regimens
- Gram-positive cocci: Vancomycin
- Gram-negative cocci: Ceftriaxone
- Gram-negative bacilli: 3rd generation cephalosporin (e.g., ceftazidime), cefepime, piperacillin-tazobactam, or carbapenem
- No organism on gram stain but strong suspicion for bacterial septic arthritis: IV vancomycin plus either ceftazidime, cefepime, or an aminoglycoside
- Start serial drainage with lavage
- Sometimes debridement (arthroscopic or open approach) is necessary
- Tailor antibiotics to gram stain, culture and susceptibility results when available (see table below)
- Continue antibiotic therapy at least ≥ 2 weeks
- Continue serial drainage as needed
- Immobilization + NSAIDs for pain relief and to reduce inflammation
- Follow-up: Physiotherapy should be initiated early to prevent contracture of both the joint and its capsule
Treatment of adults after culture has returned
|S. aureus and other gram-positive cocci|
|N. gonorrhea|| |
Treatment of children
- ≤ 3 months: oxacillin + gentamicin
- > 3 months: nafcillin + cefazolin