OSTEOMYELITIS
Micro Exam 6

  • Progressive infection of bone
  • Inflammatory destruction --> new bone made

3 Categories Based on Mechanism of Infection

  1. Secondary to Contiguous Focus of Infection
    • Trauma, surgery, insertion prosthetic device
    • Children - surgery
    • Older Adults - decubitus ulcers, infected joints
  1. Secondary to contiguous focus of infection assoc. with vascular insufficiency
    • DM or PVD
  1. Following hematogenous spread of infection
    • Major mechanism of long bone (children) & vertebral (adult) infection)
    • Occurs more commonly children (<17 yrs age)
    • Adults (>50 yrs) - Lumbar most common
    • Adults (< 40 yrs) Sternoclaficular & Pelvic bones - IVDU

Microbial Etiologies

Gram ➕

Gram ➖

Staph aureus
🌟Case Study

Coagulase-Negative Staphylococcis (CoNS)

Staph Epidermis

Staph saprophyticus

GBS
Strap agalactiae

  • Neonates <1 mo

Strep pneumoniae

  • Older infants, children, adults

Salmonella

  • Sickle cell disease

Serratia marcescens

  • SLOW lactose fermenting enterobacter
  • IVDU

E. coli

  • Neonates (< 1mo)

H. Influenzae Type B

  • Incomplete vaccination

Aerobic gram-negative rods

  • Trauma or surgery
  • IVDU
  • Infection after puncture wound (ex. foot)

⭐ Kingella Kingae

  • Aerobic

Pediatric ostoarticular infections, bacteremia, endocarditis

  • Colonized posterior pharynx of young children
  • Transmitted child to child (close contact)
  • Daycare

ID:

  • Improved culture methods
  • Nucleic Acid Amplification techniques
  • Grows SLOW in high density microbiota background

Virulence Factors

RTX Toxin ⭐potent

  • Pore-forming cytotoxin

Type IV Pili = Adhesin

  • Twitching motility
  • Adhere substrate > contract via polymerization/depolarization
  • Same pilus = DNA transfer

S&S:

  • Subtle
  • Normal levels of acute phase reactants
  • HIGH INDEX OF SUSPICION required

💊 Treatment:

  • B-lactams Penicillin or Cefazolin for Chronic Osteomyelitis

Typically respond well to antibiotics, except in cases of endocarditis

  • Hematogenous & contiguous focus osteomyelitis
  • Adhere to fibrinogen, fibrinonectin, laminin, collagen, bone, sialoglycoprotein

Virulence Factors

1. Microbial Surface Components (MSCRAMMS)

  • Clumping factor A = coagulase & binds platelets
  • Fibronectin Binding Proteins (FnBPA & B)
    • rapidly coats implanted foreign bodies in vivo
    • may play role in binding to implants

2. Virulence determinants of bacteria
EX:

  • Taken up by osteoblasts & develop resistance
  • Assoc. w/ Chronic Osteomyelitis (high relapse rate when treated w/ short duration therapy)

Protein A 🔗 Fc part of IgG
&
🚫Opsinization by PMNs

Secretes Superantigens

  • Avoids cellular & humoral immune system

Enterotoxins

  • SEA
  • SEB

TSST-1

3. Biofilm Formation

  • Polysacc., protein, & extracellular DNA
  • Coat organic & inorganic surfaces
  • Create bacteria community
  • Density & depth of biofilm protects from antimicrobials & antibodies

Pathogenesis

  • Long bones in children

Hematogenous Osteomyelitis

  • MONOmicrobiotic
  • Metaphysis = *⃣ common site of infection
  • Phagocytes migrate to area of infection
  • Produce inflammatory exudates = metaphyseal abscess

add image slide 19

  • Increase intramedullary pressure
  • Exudate extends into bone cortex
  • Ruptures through periosteum
  • Periosteal blood supply interrupted

NECROSIS

Sequestrum

  • Separated pieces of dead bone
  • Hallmark of Chronic Osteomyelitis

Involucrum

  • New bone formation in area of periosteal damage

Acute Osteomyelitis

  • Infection in bone BEFORE development of sequestra

Chronic Osteomyelitis

  • Presence of dead bone - sequestrum = HALLMARK

Other hallmarks:

  • Formation of an involucrum (new bone)
  • Local bone loss
  • Sinus tracts (extension of infection through corticol bone to surface)

Rate

Slow

  • Vetebral osteomyelitis

Fast

  • Prosthetic devices
  • Compound fractures

Contiguous Osteomyelitis

  • Either POLY or MONOmicrobiotic
  • Gradual onset over several days:
  • Fever, rigors, limp
    OR
  • Dull pain at site
    OR
  • Inability to walk (children)
    OR
  • Redness & Swelling around a long bone
  • Also, HEET

Associated with SEPTIC ARTHRITIS

  • Infection from metaphysis spreads
  • Breaks through cortex w/capsular reflection of joint
  • Secondary infection
  • Joints: long bone metaphysis w/in joint capsule reflections (knee, hip, shoulder)
  • Infants:
    • long bones --> quickly becomes septic arthritis

2 weeks = Bone Inflammation S&S

  • Pain, erythema, edema
  • Xray = deviatlized bone

Pt typically has inadequate duration of therapy

Associated with Deep/Extensive ULCERS (pedal)

  • fail to heal after several weeks of care
  • Esp. if ulcer is over bony prominence

DM Patients

  • Probe bone
  • Probing bone sufficient for diagnosis

Associated with Poor Management

  • 6 wks post-orthopedic repair & oral antibiotics
  • No debridement surgery of malleolar fracture
  • S. aureus infection

On XRAY (Subacute/Chronic Osteomyelitis):

  • Brodie Abscess

On MRI

  • Penumbra sign (differentiates from bone tumor)

Diagnosis

  • Clinical manifestations (inappetence, focal symptoms, fever)
  • Isolate (sterile) from bone biopsy >> Blood cultures
  • Histological findings of inflammation & osteonecrosis

Components to Support Diagnosis:

  • Radiological or MRI imaging
    • Bone biopsy to confirm dx:
      • Sample 1: Gram Stain & Culture
      • Sample 2: Histology
  • Resposne to empiric therapy

Labs (few days to show up):

  1. Leukocytosis
  2. Elevated ESR or 'sed rate' - slow decline
  3. Elevated CRP - 🌟 most responsive
    • 10 minute finger stick blood sample

💊 Treatment:

  • Ortho consult
  • Antimicrobials (appropriate for age & condition)
  • Monitor 36 h
    • Pain, fever, CRP should decrease
  • If indicators no change or increase, re-evaluate & make adjustments
    • MRI

💊 Treatment:

  • Debridement of necrosis & surgery
  • Antimicrobials (wait until tissue culture)
    • If CA-MRSA, could be risky to wait
  • Parenteral administration

Duration:

  • Continue until debrided bone covered w/ vascularized soft tissue
  • = or > 6 wks from last debridement

Adjunctive therapies

  • HBO: Hyperbaric Oxygen Therapy
  • Negative pressure wound therapy 🌟 (vacuum assisted closure)

NORMAL plain Xray does not R/O Acute Osteomyelitis
MRI best

Early Empiric Antibiotic for AO depends on prevalence of CA-MRSA


Switch to ORAL meds with clinical improvement and decrease CRP

💊 Treatment:

  • MSSA: Nafcillin, Oxacillin, Fefazolin
  • MRSA: Vancomycin, Clindamycin