Info
🌱 來自: Huppert’s Notes
BoneJoint Infections🚧 施工中
Bone/Joint Infections
Osteomyelitis
• Types of osteomyelitis and pathogenesis:
- Hematogenous osteomyelitis: Develops in the setting of bacteremia (e.g., endocarditis or another endovascular infection). S. aureus is the most common pathogen.
- Vertebral osteomyelitis: Develops due to hematogenous spread, local tissue invasion (e.g., from a psoas abscess), or direct inoculation after a procedure. S. aureus is the most common pathogen, along with Streptococcus spp., Gram-negative rods, and Mycobacterium spp. (Pott disease = TB osteomyelitis of the spine).
- Non-hematogenous osteomyelitis: Develops in the setting of poor wound healing, such as diabetic foot ulcers and sacral decubitus ulcers, followed by direct inoculation from the skin and soft tissue to the exposed bone. Common skin flora, in addition to Gram-negative organisms (including P. aeruginosa) are the most common pathogens.
• Symptoms:
- Dull pain over the site of the infected bone, often develops gradually
- Symptoms of local infection (e.g., erythema, warmth, swelling, or tenderness) or systemic infection and bacteremia (e.g., fevers, rigors) may be present
• Diagnostic tests:
- Labs: Usually non-specific, and can include leukocytosis and an elevated ESR and CRP
- Blood cultures: Obtain in all patients prior to antibiotic administration. Blood cultures are most often positive in patients with hematogenous osteomyelitis.
- Imaging: MRI is the most sensitive imaging modality. X-ray can be useful in patients with long-standing symptoms but is not helpful in detecting early infection. CT with contrast can detect cortical irregularities but is less sensitive than MRI.
• Establishing the diagnosis: There are two ways to make a diagnosis of osteomyelitis:
- Definitive diagnosis with bone biopsy. In general, open bone biopsy (such as during debridement) has a higher diagnostic yield than needle biopsy
- An inferred diagnosis with a combination of clinical features (e.g., imaging findings, positive blood cultures)
• Treatment:
- Antibiotic therapy: Empiric therapy with vancomycin + ceftriaxone 2 g IV daily or cefepime 2 g IV q8 hr if P. aeruginosa coverage is needed. Narrow antibiotics based on culture sensitivities. Typical duration is 6 weeks.
- Surgical intervention: Bone debridement is sometimes needed, especially if bone necrosis is present. Consult an orthopedic surgeon (or a neurosurgeon in the case of vertebral osteomyelitis) to determine the need for debridement.
Septic arthritis
• Pathogenesis:
- Hematogenous seeding: Septic arthritis most commonly develops as a result of hematogenous seeding of the synovial membrane, which then extends into the joint space
- Direct inoculation: Less often, septic arthritis develops via local spread from contiguous tissues. This occurs in situations such as a bite wound or joint space procedure (e.g., arthroscopy or intra-articular injection)
• Risk factors: Rheumatoid arthritis (RA) or other conditions that cause joint pathology (e.g., osteoarthritis)
• Pathogens:
- S. aureus: Most common cause of septic arthritis, especially in patients with a prosthetic joint or RA
- Neisseria gonorrhoeae: Most common cause of septic arthritis in young, previously healthy adults
- Streptococcus spp.: Patients with functional or true asplenia are at increased risk
- Gram-negative organisms (e.g., P. aeruginosa): Immunocompromised patients are at highest risk
- Mycobacterium spp.: Patients with underlying immunocompromise or TB risk factors
• Clinical features: Red, hot, swollen, and tender joint with extreme pain with either passive or active range of motion. A joint effusion is also often present. Fever may be absent, especially in older adults.
• Diagnosis: Arthrocentesis and synovial fluid analysis. Consider the following studies:
- Synovial fluid WBC count: The likelihood of septic arthritis is directly related to the WBC count
• A synovial fluid WBC count >50K cells/µL, and especially >10K cells/µL, suggests septic arthritis. The differential is often neutrophil-predominant. Crystal arthritis (e.g., an acute gout flare) can have a similarly high WBC count and commonly mimics septic arthritis
• A synovial fluid WBC count <20K cells/µL suggests against septic arthritis
- Synovial fluid Gram stain: A positive Gram stain confirms the diagnosis of septic arthritis, but is only positive in 50% of cases; therefore a negative Gram stain does not rule out septic arthritis
- Synovial fluid culture: In cases of non-gonococcal septic arthritis, the synovial fluid culture is positive over 60% of the time
- Crystals: The presence of crystals in synovial fluid suggests crystal arthritis. Of note, patients with crystal arthropathy (e.g., underlying gout or pseudogout) can also develop concurrent septic arthritis; the presence of crystals on arthrocentesis does not exclude septic arthritis
• Treatment:
- Empiric antibiotic therapy:
• Vancomycin + ceftriaxone 2 g IV daily (no P. aeruginosa coverage)
• Vancomycin + cefepime 2 g IV q8hr (for P. aeruginosa coverage)
• Narrow based on culture results. Duration 2–4 weeks.
- Joint drainage: Surgical joint washout is the cornerstone of management to adequately control the infection. Consult orthopedic surgery for surgical decision making.