Septic arthritis due to bacterial infection is often a destructive form of acute arthritis. In most cases, bacterial arthritis arises from hematogenous spread to the joint. Bacterial arthritis can also arise as a result of a bite or other trauma, direct inoculation of bacteria during joint surgery, or, in rare cases, following extension of preexisting bony infection through the cortex into the joint space.
Bacteremia is more likely to localize in a joint with preexisting arthritis, particularly if associated with synovitis. Patients with rheumatoid arthritis appear to be especially prone to bacterial arthritis; the risk may also be increased in gout, pseudogout, osteoarthritis, and Charcot arthropathy.
Many pathogens are capable of causing bacterial arthritis. Organisms such as S. aureus and streptococci have a higher propensity to cause joint infections than gram-negative bacilli, which typically cause infections following trauma or in patients with severe underlying immunosuppression.
Patients with bacterial arthritis usually present acutely with a single swollen and painful joint (ie, monoarticular arthritis). The knee is involved in more than 50 percent of cases; wrists, ankles, and hips are also commonly affected.
The definitive diagnostic test is identification of bacteria in the synovial fluid. In the setting of suspected joint infection, synovial fluid aspiration should be performed (prior to administration of antibiotics); fluid should be sent for Gram stain and culture, leukocyte count with differential, and assessment for crystals.
Treatment of acute bacterial arthritis consists of antibiotic therapy and joint drainage. The initial choice of antibiotics for treatment of septic arthritis is based on the Gram stain. The initial regimen should be tailored to culture and susceptibility results when available. The typical duration of therapy is three to four weeks.
If the initial Gram stain of the synovial fluid shows gram-positive cocci, we suggest treatment with vancomycin (Grade 2B).
If the initial Gram stain of the synovial fluid shows gram-negative bacilli, we suggest treatment with a third-generation cephalosporin (Grade 2B).
If the initial Gram stain is negative and the patient is immunocompetent, we suggest treatment with vancomycin (Grade 2C).
If the initial Gram stain is negative and the patient is immunocompromised, we suggest treatment with vancomycin plus a third-generation cephalosporin (Grade 2C).
In general, we recommend joint drainage in the setting of septic arthritis (Grade 1B), as this condition represents a closed abscess collection. Options for drainage include needle aspiration (single or multiple), arthroscopic drainage, or arthrotomy (open surgical drainage).
No randomized controlled studies have evaluated antibiotic regimens for bacterial arthritis. The initial choice of antimicrobial regimens is based on coverage of the most likely organisms to cause infection in this setting, the Gram stain, the clinical presentation, and data from case series.
If the initial Gram stain of the synovial fluid shows gram-positive cocci, treatment with vancomycin (30 mg/kg per 24 hours in two equally divided doses, not to exceed 2 g per 24 hours unless concentrations in serum are inappropriately low) should be administered.
If the initial Gram stain of the synovial fluid shows gram-negative bacilli, treatment with a third-generation cephalosporin should be administered. Regimens include:
Ceftriaxone (2 g intravenously once daily) or
Cefotaxime (2 g IV every eight hours) or
Ceftazidime (1 to 2 g intravenously every eight hours)
In the setting of clinical suspicion for Pseudomonas aeruginosa (eg, in patients who inject illicit drugs), ceftazidime should be given with an aminoglycoside such as gentamicin (3 to 5 mg/kg per day in two or three divided doses); the regimen may be streamlined to a single agent once antimicrobial susceptibility data are available. In cephalosporin-allergic patients, treatment with ciprofloxacin (400 mg IV every 12 hours or 500 to 750 mg orally twice daily) may be administered (in addition to an aminoglycoside).
●If the initial Gram stain is negative and the patient is immunocompetent, treatment with vancomycin should be administered. If the initial Gram stain is negative and the patient is immunocompromised, treatment with vancomycin plus a third-generation cephalosporin should be administered. The same regimen is appropriate in the setting of traumatic bacterial arthritis and for injection drug users.
The initial regimen should be tailored to culture and susceptibility results when available. As an example, vancomycin should be discontinued in patients with staphylococcal or streptococcal infections that are susceptible to beta-lactam therapy. Septic arthritis due to methicillin-resistant S. aureus (MRSA) should be treated with vancomycin; if this is not feasible due to allergy or drug intolerance, reasonable alternative agents include daptomycin (6 mg/kg/day IV), linezolid (600 mg by mouth [PO] or IV twice daily), or clindamycin (600 mg PO or IV three times daily).
There is no role for intraarticular antibiotics; parenteral and oral antibiotic therapy produce adequate drug levels in joint fluid. Furthermore, direct instillation of antibiotics into a joint may induce an inflammatory response.
Duration of therapy
There have been no controlled trials examining the duration of antimicrobial therapy in bacterial arthritis; treatment recommendations are based on case series. We typically administer parenteral antibiotics for at least 14 days followed by oral therapy (if possible) for an additional 14 days. However, selected patients with infections due to organisms that are susceptible to oral agents with high bioavailability (such as a fluoroquinolone) can be successfully treated with a short course (4 to 7 days) of parenteral therapy followed by 14 to 21 days of oral therapy. Compliance and response to therapy should be monitored carefully in such patients.
Longer courses of outpatient parenteral antibiotic therapy (eg, three to four weeks) may be necessary to cure infections due to difficult-to-treat pathogens such as P. aeruginosa or Enterobacter spp. In addition, a longer course of therapy (four weeks) is warranted in the setting of bacteremia and arthritis associated with S. aureus.