2. MTB Step 3 - Osteomyelitis

Question 1

OSTEOMYELITIS

1. What are the top (3) Most Likely Bacterial causes of Osteomyelitis?
2. What are (5) Predisposing Risk Factors for Osteomyelitis?

Answer 1

Cause/Causal agent:

• Staphylococcus aureus (Gram-pos)
• Salmonella (Gram-neg Bacilli)
• Pseudomonas (Gram-neg Bacilli)

Predisposing factor(s):

• Diabetes (DM) w/ an ulcer or soft tissue infection.
• Peripheral Arterial Disease (PAD) w/ an ulcer or soft tissue infection.
• Both (DM & PAD) w/ an ulcer or soft tissue infection.
• Direct Trauma.
• Hx of Orthopedic Surgery.

Question 2

OSTEOMYELITIS

What is the Pathophysiology (underlying processes/pathways) for Osteomyelitis?

Answer 2

Underlying Processes/Pathways:

• Tissue injury stimulates the release of a number of chemical mediators that promote vasodilation, chemotaxis, and binding of neutrophils and macrophages to area capillaries. These events facilitate the emigration of neutrophils and macrophages into the tissue, where they begin phagocytosis.

Question 3

OSTEOMYELITIS

What is the typical Clinical Presentation of Osteomyelitis?

Answer 3

Ulcer or Soft Tissue Infection in a patient with Diabetes (DM), Peripheral Arterial Disease (PAD), or both with an …

YOU NEED TO

…distinguish the difference between a soft tissue infection and a contiguous spread into the bone.

Question 4

OSTEOMYELITIS

What are the various drugs and their mechanisms of action used to treat Gram + Osteomyelitis?

Answer 4

MSSA:

• Oxacillin or Nafcillin - The β-lactam ring of the antibiotic forms an irreversible covalent acyl bond with the transpeptidase enzyme, preventing the crosslinking reaction.

MRSA:

• Vancomycin, Dalbavancin, Oritavancin - glycopeptide that binds to the terminal d-alanine-d-alanine component of the stem peptide while the subunits are external to the cell membrane but still linked to the lipid carrier. This binding sterically inhibits the addition of subunits to the peptidoglycan backbone.
• Linezolid - oxazolidinone that binds to the 50S ribosomal subunit and blocks the initiation of protein synthesis.
• Ceftaroline - β-lactam, so binds to penicillin-binding proteins (PBPs) in both gram-negative and positive bacteria and prevents their capability to act as transpeptidases in bacterial cell wall formation.
• Daptomycin - disrupting multiple aspects of bacterial cell membrane function. … This causes rapid depolarization, resulting in a loss of membrane potential leading to inhibition of protein, DNA, and RNA synthesis, which results in bacterial cell death.

Question 5

Diagnosis

1. What is the Best INITIAL Diagnostic Test for Osteomyelitis?
2. What is a MORE Accurate Diagnostic Test for Osteomyelitis?
3. What is the Most ACCURATE Diagnostic Test for Osteomyelitis?

Answer 5

1. Best INITIAL Test = X-Ray –> Periosteal elevation
2. MORE Accurate Test = MRI (if X-Ray is normal)
3. Most ACCURATE Test = Bone Biopsy

Question 6

What is the only form of Osteomyelitis that can be successfully and reliably treated with Oral Antibiotics?

Answer 6

Gram-negative Bacilli (Salmonella & Pseudomonas)

Question 7

You MUST confirm Gram-negative Osteomyelitis prior to treatment. What is the Diagnostic Method for doing so?

Answer 7

Bone Biopsy

Question 8

For which Type of Osteomyelitis (acute vs chronic) is there NO urgency to treat?

Answer 8

CHRONIC Osteomyelitis (obtain the biopsy, move the clock forward, and treat what you find on the culture)