Musculoskeletal Infections

Question 1

Pathophysiology, Etiology, Clinical Presentation, Diagnosis and treatment of Septic Arthritis.

Answer 1

• Infection of the joint
  
  • Etiology: Hematogenous seeding of joint (bacteria from the blood!), may be transient! Easier for bacteria to get from blood to join! Other mechanisms:
    
    • Post-operative, penetrating trauma, contiguous skin/soft tissue infection
    • Viral infections
    • 10x more common among people with rheumatoid arthritis!!
• Clinical Presentation: hot, swollen, painful joint, limited range of motion. Often knees, hipes, ankles! 1/2 have high fever.Common sources of bacteremia.. is SKIN!
• Diagnosis:
  
  • Radiographs (xRays), necessary but rarely helpful!
  • Blood cultures! positive in 1/2 of cases
  • Joint fluid aspirate(most useful)… then look at under microscope.. cell count/differential, gram stain, cultures! Most important are CELL COUNT AND CULTURE.
  • WE LOOK AT CRYSTALS ON ANALYSIS TO SEE IF THEY HAVE GOUT OR PSEUDOGOUT!!!**
• Most common microorganisms causing:
• Staphylococcus aureus
• Streptococci pyogenes
• Treatment: Source control.
  
  • Repeated aspiration
  • Open surgery to drain pus
    
    • If S. Aureus - cloxacillin/cefazolin
  • If MRSA - Vancomycin
  • GNB - ceftriaxone

Question 2

Describe pathophysiology, etiology, clinical presentation, diagnosis and treatment of osteomyelitis in children and adults

Answer 2

• Infection of the joint
• Etiology: Hematogenous seeding (main route for infection in children), after trauma, contiguous focus of infection.. overlying soft tissue infection. Adults = long bones, pelvis, clavicle. Children = only long bones. Men 2x more likely than women.
• Clinical Presentation: Pain, Fever, Sweats, loss of function. localized swelling, if vertebrae inolved may develop epidural ABSCESS.
• Microbiology: if hematogenous seeding = monomicrobial (S. Aureus). If from trauma = polymicrobial… S. Aureus
• Diagnosis: - Usually nothing to aspirate. Difficult to obtain bone for culture, blood cultures sometimes positive (should be done!)
  
  • Imaging: Plain xrays not very sensitive, can take 2 weeks to see any changes.. Can do Bone scan - (take isotope which you inject then is taken up by osteoblastic cells), Has 3 phases… flow phase, blood pool phase, and delayed phase. If osteomyelitis is present.. images will be hot in all three phases. Bone scans can be positive after just 48 hours after symptoms onset!! MRI is excellent for differentiating soft tissue infection from bone infection, it is the PREFERRED IMAGING for osteomyelitis.
  • Blood Tests: Inflammatory markers in blood.Use Erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP), isn’t very specific.. can be caused by MANY inflammatory conditions…
  • Culture: Blood or tissue required. Swabs from sinus tracts very UNRELIABLE! But Bone biopsy is the BEST specimen.. but often difficult to obtain!
• Treatment: - Surgical: Remove any necrotic bone. Remove foreign bodies. Cover exposed bone with soft tissue. Cover any exposed bone with soft tissue (skin flaps)
  - Antimicrobials … same as Septic Arthrytis! S. Aureus = cloxacillin/cefazolin. MRSA = Vancomycin. GNB = ceftriaxone. 2 weeks parenteral therapy. 6 weeks total treatment.

Pediatrics: Osteomyelitis - most often hematogenous in children. Osteomyelitis and septic arthritis often occur together. Clinical presentatoin is loss of function! Hips involved with septic and need ot be drained! S. Aureus still primary pathogen.. but lots of MRSA! . S. Agalactiae more common in neonates! Kingella Kingae… common septic and osteo in young children! Treatment courses are SHORTER! Few days IV then switch to oral!