Academic Day Seminar – Feb 10 (Osteomyelitis)

✔ Osteomyelitis

Condition: Infection localized to the bone

Classifications:

  • Hematogenous: bloodstream (mono-microbial) – 19%
    • more common in children (metaphysis of skeletally immature patients → bone plates are still growing and requiring abundant blood supply)
    • in adults, vetebra most common site (lot of blood supply which is also “sluggish” in this location)
  • Contiguous: adjacent soft tissue infection gains access to bone (polymicrobial) – 47%
    • younger individuals with trauma, open fx, surgery
    • older adults secondary to decubitus ulcers & infected total joint arthroplasties
    • Can affect any bone; RF: fractures, surgery, prostheses
  • Peripheral vascular disease – 34%
    • Diabetes
  • Acute: < 2 weeks
    • Introduction of microbes into bone → tissue necrosis
    • Difficult for host inflammatory cells and abs to reach necrotic area
  • Subacute (2-4 weeks)
  • Chronic: >4 weeks or relapse
    • Appearance of dead bone, fistulous tracts

Pathogens:

  • Hematogenous: mono-microbial, S. aureus
    • IVDU: G(-)s: Pseudomonas (80%)
      • Pseudomonas lives ins most water/soil – so if use dirty water for IVDU, would increase risk of Pseudomonas
    • >50 y/o: tend to see more G-s (e.g. E coli) d/t more UTIs in this pt pop
  • Vertebral:
    • Lumbar + Thoracic
    • S. aureus 60%
    • E. coli
    • Mycobacterium tuberculosis
  • Sickle cell anemia:
    • Salmonella 66%
    • Bowel infarction facilitate salmonellae bacteremia
  • Contiguous
    • Polymicrobial or monomicrobial
    • S. aureus most common
    • S. epidermidis, P. aeruginosa, E. coli, Proteus, Strep, anaerobes
  • Vascular insufficiency
    • Polymicrobial
    • Staph, Strep, Enterobactericiae, Enterococcus, Bacteriodes, anaerobes
    • RF: pressure sores, DM, PVD; Often bone in feet involved
Diagnostics Clinical Presentation
  • Probe to bone
  • Imaging:
    • Xrays (bone changes not seen until 14 ds)
    • MRI: preferred; sensitive as early as 3-5 ds (observes infection presence and extent, distinguishe between soft tissue and bone infection)
    • CT scan: modaility of choice if no MRI (not as sensitive or specific as MRI)
    • Bone scan: accumulates in osteoblastic activity (therefore distinguish OM from cellulitis; low sensitivity, esp with recent trauma or surgery)
    • Gallium scan: affinity to acute phase reactants + areas of inflammation; may combine with bone scan
    • WBC scan: sites of inflammation or infection;
      Combining with bone scan can increase specificty
  • Lab:
    CRP, ESR
  • CXs
    – Bone aspiration/biopsy
    – intra-op tissue cx
    – BCx
    – Open wounds and draining sinuses contaminated
CNS: +/- Fever
MSK: Localized bone pain/tenderness, warmth, decreased limb motion
DERM: redness, edema in affected area
Labs: WBCs, ESR, CRP may increase
ID: BCx + in 50% with hematogenous OM. Perform bone aspiration, biopsy, bone Cx

  • Hematogenous:
    – pain, tenderness, warmth, erythema, swelling, reduced range of motion, fever, chills, malaise
    – vertebral OM: severe dull back pain, may have systemic symptoms
  • Contiguous:
    – localized pain, tenderness, warmth, edema, erythema
    – post-surgical: sxs manifest within 1 mos as pain
  • vascular insufficiency
    – pain, erythema, redness
    – bone exposed assume

Complications

  • Local bone damage, necrosis
  • apposition of new bone
  • recurrence
  • sepsis
  • mortality

GoTs:

  • Treat the infection
  • Restore bone and joint function
  • Prevent progression to chronic OM
    • Chronic → poorer prognosis as necrotic bone acts as bacterial reservoir and inability to remove all dead bone may require suppressive therapy
  • Prevent recurrence
  • Minimize ADRs

Treatment

  • Starting empirically:
    • For stable patients or those with stable OM: when cxs are obtained during debridement or bone biopsy
    • For septic, hemodynamically unstable or have neurological compromise: right away
  • Modify therapy based on micro
  • Treat for 4-6 weeks – consider treating for 8 weeks if drug-resistant e.g. MRSA

Concepts

  • Go HIGH (but relationshiop b/w dose and concentration in bone and therapy outcome unknown) and Go IV
  • Good penetration: B-lactam, cephalosporin, clindamycin, fluoroquinolones, septra, doxycyline, metronidazole
    • But…NOT oral B-lactams
    • Metronidazole dosed Q8H not Q12H
  • When to step down → afebrile, clinically stable and improving, can tolerate PO intake, adherent medicallys
    • Not neonates or immunocompromised
    • Generally in 2 weeks (based on small retrospective study)
  • SOURCE CONTROL: debridement, removal or hardware, revascularization
    gnerally considered for: chronic OM, DFI, worsening infection despite antimirobial tx

✔ Prosthetic Joint Infection

Condition: Infection of joint replacements (can occur after total hip arthroplasty, or total knee rthroplasty) → Can lead to loss of joint function and structure, mobility, risk of sepsis, mortality

Pathophysiology: prosthesis allow for biofilm to develop → biofilm protects microbes from host → as biofilm develops, microbes less susceptible to antimicrobials

Common organisms:

Onset Microbes introduced Common organisms
Early (within 3 months) At time of surgery Staph aureus, GNB, anaerobes
Delayed (3-12 months) At time of surgery CoNS Staph, Enterococci
Late (>12 months) Hematogenous source Staph aureus, beta-hemolytic streptococci, GNB

Assessment:

  • Symptoms: acute onset or chronic pain unresolved by joint replacement
  • Persistent wound drainage around prosthesis
  • ESR and CRP may increase
  • Imaging tests: X-ray
  • Gram stain: only 1/3 positive (low sensitivity)
  • Joint culture: highly sensitive and specific
  • Joint fluid analysis: Increased WBCs and neutrophils, purulence

Treatment

  • Source control: debridement and prosthesis retention, prosthesis removal, amputation, resection arthroplasty
  • Duration of abx: 4-6 weeks, except for Staphylococci – treat for 2-6 weeks with IV abx (+ rifampin PO 300mg BID) then switch to PO abx (+ rifampin PO 300mg bid) for total 3-6 months (6 mos if receiving TKA)
    • Rifampin can penetrate into biofim, has synergistic activity in combintion with other antimicrobials …but NOT to be given as monotherapy or before surgical intervention due to risk of rapid resistance development in presence of high bacterial inoculum size
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