fong - osteomyelitis

osteomyelitis

inflammation of the bone caused by an infecting organism (monomicrobial > > > polymicrobial)

• contiguous (trauma, surgery, SSTI progression)

• hematogenous (bacteremia from another source)

• vascular insufficiency (diabetic foot infection — polymicrobial)

epidemiology and risk factors

• diabetes

• recent injury (broken bones)

• orthopedic surgery (bone/joint repair)

• IVDU (IV drug use)

• dialysis

• catheter use

• immunosuppression (malignancy, liver disease, etc)

• anything that increases gram-positive bacteremia risk

microbiology

• S. aureus

  • up to 1/3 MRSA

• group B Streptococcus

  • newborns

• GNR’s

  • contiguous > hematogenous

• fungal (rare)

• mycobacterial (rare)

osteomyelitis pathophysiology

clinical presentation

diagnostic tools (imaging)

• X-ray:

  • helps rule out other diagnoses but not very sensitive

• CT scan:

  • can reveal extent of destruction and guide bone biopsies

  • less useful than MRI but less costly

• imaging:

  • MRI is most sensitive and specific

  • can detect infection days after onset

diagnostic/monitoring tests

• WBC

  • not reliably elevated, especially in chronic osteomyelitis

• C-reative protein (CRP)

  • produced by liver in response to any infection (non-specific)

  • elevated within hours of infection

  • should return to normal within a week after appropriate antibiotics

• Erythrocyte sedimentation rate (ESR)

  • generally elevated in osteomyelitis, but slower responder than CRP

*NOT very useful diagnostics, but helpful for monitoring

diagnostic cultures

• recommend withholding antibiotics until cultures obtained

  • osteomyelitis usually not acute illness presenting with hemodynamic instability

• blood culture

  • unlikely positive unless systemic signs of infection (SIRS)

• bone biopsy

  • gold standard to identify organism + bone destruction, but difficult to obtain

• wound culture (e.g, diabetic foot)

  • very limited utility, can capture the wrong bugs unless done in sterile surgery

good quality cultures are crucial for appropriate treatment

surgery (source control)

• must eliminate dead bone (mainly chronic osteomyelitis)

  • difficult for vertebral (spinal) osteomyelitis

• radical debridement until down to living bone

  • inadequate debridement leads to recurrence

  • may require reconstruction if it results in large dead space

    • bone grafts, antibiotic beads, muscle flaps

• last resort is amputation

treatment

landmark trial: OVIVA

• RCT of 1054 patients with osteomyelitis to receive IV or oral antibiotics within 7 days of surgery or start of therapy

• primary outcome: treatment failure at 1 year

• oral antibiotics noninferior to IV antibiotics

treatment duration

acute (uncommon in adults):

• antibiotics alone may be sufficient

• treatment duration: 4-6 weeks

subacute/chronic:

• surgery likely required for tissue/bone removal

• treatment duration: ≥ 6 weeks

treatment duration for subacute/chronic begins when removal of necrotic bone/tissue is complete (if possible)

• takes 6 weeks for bone to be covered by vascularized tissue

• can monitor normalization of CRP/ESR ± repeat imaging

presence of foreign material/hardware may require lifetime suppression

osteomyelitis with hardware

• highest risk of infection within 2 years of hardware implantation

• most likely organism: S. aureus or S. epidermidis

• add rifampin 450 mg IV/PO BID

  • rifampin to penetrate biofilm formation on prosthetic material

if no cultures, what do you do?

• cover for likely pathogens

  • S. aureus (consider MRSA risk factors)

  • Streptococci spp.

  • gram-negatives if contaminated/trauma or immunocompromised

• if diabetes-related (foot infection):

  • consider adding gram-negative and anaerobic coverage

• potentially requiring ≥ 6 weeks of vancomycin ± ceftriaxone or piperacillin-tazobactam?

osteomyelitis monitoring

• clinical improvement

  • symptoms decrease (pain, tenderness, warmth, etc)

  • improved movement

  • CRP, ESR to monitor inflammatory response (WBC likely not helpful)

  • imaging to demonstrate improvement/completion of treatment

• must monitor antibiotics considering long duration, to name a few:

  • vancomycin: levels, AKI

  • nafcillin/oxacillin: AKI (AIN), hepatoxicity, blood dyscrasias

  • daptomycin: rhabdomyolysis

  • fluroquinolones: separate from divalent cations

  • all antibiotics: C. difficile

septic arthritis

• infection of joint

  • bacteria > fungi/mycobacteria

  • hematogenous or direct

• 4-10 per 100,000 patients-years

• risk factors:

  • rheumatoid or osteoarthritis

  • joint prosthesis

  • IV drug use

  • alcholoism

  • diabetes

  • intra-articular corticosteroid use

  • SSTI

• complications: osteomyelitis, mortality (up to 10%)

septic arthritis: symptoms and diagnosis

• 1-2 weeks of erythema, pain, fever, and restricted joint movement

  • “hot joint”

  • less common: sweats, rigors

• blood cultures positivity: < 20%

• get synovial (joint) fluid aspirate, but can be difficult

  • WBCs > 50,000/microliter highly suggestive of infection

• antibiotics should be withheld prior to cultures unless patient is hemodynamically unstable

microbiology

empiric treatment

no MRSA risk factors = uncommon

most likely: vancomycin + ceftriaxone

*any MRSA + ceftriaxone

definitive treatment and management

• de-escalate based on cultures (blood or synovial)

  • if culture negative, likely stuck with vancomycin ± ceftriaxone

• duration of treatment

  • 2 weeks of IV therapy THEN at least 2 weeks of oral therapy

• monitoring

  • like osteomyelitis

diabetic foot infections (DFI) pathophysiology

diabetic food infections (DFI) management

• goal: cure infection without amputation

• antibiotics alone often fail and amputation often required due to:

  • poorly controlled diabetes

    • poor blood flow —> poor drug delivery

    • impaired immune system

  • necrotic tissue

  • osteomyelitis

  • prolonged therapy (adherence)

• location (foot) increases chance of polymicrobial infection

  • skin, dirty, less oxygenation

  • anaerobes: often covered, especially if dead tissue present

DFI empiric therapy

cover: MSSA/MRSA + GNR (± Pseudomonas) ± anaerobes (B. fragilis+)

1. vancomycin OR linezolid OR daptomycin AND

2. ceftriaxone OR ciprofloxacin OR cefepime OR pip-tazo OR meropenem AND

3. metronidazole (unless using piperacillin-tazobactam or meropenem)

DFI definitive therapy

treat cultured organisms ± anaerobes (B. fragilis, etc)

• if adequate debridement of dead tissue, anaerobic coverage NOT required

• can use oral antibiotics

DFI antibiotic duration

• adequate source control: 0-5 days

  • e.g. amputation with clean margins

• mild (SSTI): 1-2 weeks

  • no bone involvement

• moderate/severe (deeper/larger SSTI): 2-3 weeks

• osteomyelitis: ≥ 6 weeks

  • try to avoid this duration by doing amputation

treatment take home points