Arthritis, Nongonococcal Acute Bacterial (Septic)

Essentials of Diagnosis

• Acute onset of inflammatory monarticular arthritis, most often in large weight-bearing joints and wrists

• Common risk factors include previous joint damage or injection drug use

• Infection with causative organisms commonly found elsewhere in body

• Joint effusions are usually large; white blood cell counts commonly > 50,000/mcL

General Considerations

• Most often due to hematogenous seeding of the joint; direct inoculation from penetrating trauma is rare

• Key risk factors are

  • Bacteremia (eg, injection drug use, endocarditis, infection at other sites)

  • Damaged (eg, from rheumatoid arthritis) or prosthetic joints

  • Compromised immunity (eg, advanced age, diabetes mellitus, advanced chronic kidney disease, alcoholism, cirrhosis, or immunosuppressive therapy)

  • Loss of skin integrity (eg, cutaneous ulcer or psoriasis)

• Staphylococcus aureus is the most common cause of nongonococcal septic arthritis, accounting for about 50% of all cases

• Methicillin-resistant S aureus (MRSA) and group B streptococcus are frequent and important causes of septic arthritis

• Gram-negative septic arthritis is seen in injection drug users and in other immunocompromised patients

• Staphylococcus epidermidis is the usual organism in prosthetic joint septic arthritis

Symptoms and Signs

• Acute onset, with pain, swelling, and heat of affected joint—most frequently the knee

• Unusual sites, such as the sternoclavicular or sacroiliac joint, can be involved in injection drug users

• Chills and fever are common (but absent in up to 20% of patients)

• Infection of the hip usually does not produce apparent swelling but results in groin pain greatly aggravated by walking

• More than one joint is involved in 15% of cases; risk factors include rheumatoid arthritis, associated endocarditis, and infection with group B streptococci

• Polyarticular septic arthritis is uncommon except in patients with rheumatoid arthritis or with group B streptococcal infections

• Manifestations of prosthetic joint infection are influenced by whether the infection is early (≤ 3 months after surgery), delayed (3–12 months after surgery), or late (> 12 months after surgery)

  • Early infections

    • Acute redness and swelling

    • Usually caused by S aureus and gram-negative organisms

  • Delayed infections

    • Pain is common but only 50% will have fever

    • Most commonly caused by less virulent organisms, such as coagulase-negative staphylococcus, Proprionibacterium acnes, and enterococci

  • Late infections

    • Acute pain, swelling and fever

    • Often caused by hematogenous seeding of S aureus, gram-negative bacilli, and hemolytic streptococci

Differential Diagnosis

• Gout and pseudogout are excluded by the failure to find crystals on synovial fluid analysis

• Chronic Lyme disease commonly manifests as inflammatory monarthritis of the knee, but the synovial fluid is Gram stain and culture negative

• Acute rheumatic fever commonly involves an inflammatory migratory oligoarthritis

• Pyogenic arthritis may be superimposed on other types of joint disease, notably rheumatoid arthritis

Laboratory Tests

• Blood cultures are positive in approximately 50% of patients

• The leukocyte count of the synovial fluid is always inflammatory (> 2000/mcL), usually exceeds 50,000/mcL and often is > 100,000/mcL, with ≥ 90% polymorphonuclear neutrophils

• Gram stain of the synovial fluid is positive in 75% of staphylococcal infections and in 50% of gram-negative infections

Imaging Studies

• Radiographs are usually normal early in the disease, but evidence of demineralization may develop within days of onset

• MRI and CT are more sensitive in detecting fluid in joints that are not accessible to physical examination (eg, the hip)

• Bony erosions and narrowing of the joint space followed by osteomyelitis and periostitis may be seen within 2 weeks

Diagnostic Procedures

• Joint aspiration is required to establish the diagnosis

Medications

• If the likely causative organism cannot be determined clinically or from the synovial fluid gram stain, treatment should be started with broad-spectrum antibiotics effective against staphylococci (including MRSA), streptococci, and gram-negative organisms

• Initial treatment is to give vancomycin (1 g intravenously every 12 hours, adjusted for age, weight, and kidney function) plus a third-generation cephalosporin

  • Ceftriaxone, 1–2 g intravenously daily (or every 12 hours if concomitant meningitis or endocarditis is suspected)

  • Cefotaxime, 1–2 g intravenously every 8 hours

• Antibiotic therapy should be adjusted when culture results become available

• Duration of antibiotic therapy is usually 4–6 weeks

• Options for treating prosthetic joint infections

  • Chronic suppression

  • Debridement without removal of the prosthesis

  • One- or two-stage exchange of the prosthesis

Surgery

• Effective drainage is usually achieved through early arthroscopic lavage and debridement

• Open surgical drainage should be performed when

  • Conservative treatment fails

  • There is concomitant osteomyelitis requiring debridement

  • The involved joint (eg, hip, shoulder, sacroiliac joint) cannot be drained by more conservative means

Therapeutic Procedures

• Immobilization with a splint and elevation are used at the onset of treatment. Early active motion exercises as tolerated will hasten recovery

Complications

• Bony ankylosis and articular destruction occur if treatment is delayed or inadequate

Prevention

• There is no evidence that patients with prosthetic joints undergoing procedures should receive antibiotic prophylaxis to prevent joint infection unless the patient has a prosthetic heart valve or the procedure requires antibiotics to prevent a surgical site infection

• However, the American Academy of Orthopedic Surgeons advocates prescribing antibiotic prophylaxis for any patient with a prosthetic joint replacement undergoing a procedure that can cause bacteremia

Prognosis

• With prompt antibiotic therapy and no serious underlying disease, functional recovery is usually good

• The mortality rate is 30% for patients with polyarticular infections and sepsis

When to Refer

• Refer to an orthopedist if the infected joint is not easy to aspirate repeatedly (eg, hip)

When to Admit

• Admit for presumed or confirmed septic arthritis