20 - Bone Infections

Question 1

What are the four categories of osteomyelitis? Describe each.

Answer 1

1. Hematogenous: resulting from seeding of bone related to a previous bacteremia
2. Direct Implantation: resulting from penetrating injury
3. Contiguous: resulting from direct spread of basteric from an overlying wound or pressure ulcer
4. Infection of Prosthetic Device: from infection of prosthetic material implanted in bone, with spread into adjacent bone.

Question 2

Which type of osteomyelitis tends to be more common in children and is usually monomicrobial?

Answer 2

Hematogenous osteomyelitis

Question 3

Which type of osteomyelitis tends to be more common in adults and is usually polymicrobial?

Answer 3

Contiguous osteomyelitis.

Question 4

What organisms usually cause hematogenous osteomyelitis?

Answer 4

Staph. aureus, strep. sp., gram negatives, mycobacterium tuberculosis, and salmonella sp in sickle cell pts.

Question 5

What organisms usually cause direct implantation osteomyelitis?

Answer 5

Pseudomonas aeruginosa - common in nail injuries with sneakers

Other organisms can be implanted too.

Question 6

What organisms usually cause contiguous osteomyelitis?

Answer 6

S. aureas, gram-negatives, strep. sp., anaerobes, and candida sp.

Question 7

What organisms usually cause prosthetic joint infection osteomyelitis?

Answer 7

Coagulase negative staphylocicci, S. aurea, gram negatives, strep. sp., and probionibacterium acnes.

Question 8

What organism accounts for 70-90% of hematogenous osteomyelitis cases in children?

Answer 8

Staphylococcus aureas.

Question 9

What organisms are more frequent in patients with UTIs or infections from IV drug use?

Answer 9

Gram negatives such as E. coli, pseudomonas, klebsiella, enterobacter.

Question 10

How common is it for pts with TB to have bone infections? How do these occur?

Answer 10

1-3% will have a bone infection with TB.

These can be through the bloodstream or from direct extension from a pulmonary focus (to ribs or vertebral bodies).

Question 11

What STD can infect bone?

Answer 11

Syphilis, in chronic or congenital cases.

Question 12

What has become an important pathogen in shoulder replacement infections?

Answer 12

Propionibacterium acnes.

Question 13

What are can osteomyelitis cause?

Answer 13

Chronic infections that are difficult to eradicate.

Fever (most common in acute, but rare in chronic)

Damage to periosteum may result in pieces of dead bone (sequestration) or new external bone formation (involucrum).

Localized abcesses may occur (Brodie’s abscesses).

Question 14

How would you diagnose osteomyelitis? How would you identify the bacteria?

Answer 14

X rays may be negative early in infections and are not very sensitive.

Bone/WBC scans or MRI imaging is more effective.

Bacteria can be obtained from bone biopsies or sometimes blood cultures.

Question 15

What is notoriously unreliable in determining the tyep of bacteria causing the bone infection? Why is this?

Answer 15

Cultures of open ulcers overlying contiguous osteomyelitis because the bacteria in the bone underneath may be entirely different.

Question 16

What shoild be done if a bone biopsy cannot be done or the culture results are negative (30-40% of the time)?

Answer 16

Empiris treatment would be needed.

Question 17

What type of bone infections are particularly difficult to treat?

Answer 17

Those of prosthetic materials; the prosthesis often needs to be removed to eradicate the infection.

Biofilms may develop on infected bone or on prostheses, making infections more difficult to treat.

Question 18

What are biofilms?

Answer 18

Aggregations of microorganisms adherent to a surface, particularly a hard surface like bone or teeth or prosthetic materials.

• frequently embedded in a matrix that they produce called slime or extracellular polymeric substance or glycocalyx.

Question 19

Describe the biochemistry of biofilm bacteria?

Answer 19

The biochem and physiology of biofilm organisms are different from those of planktonic (suspended) organisms.

They are likely to be more resistant to antibiotics than are planktonic bacteria.

Question 20

What does treatment of osteomyelitis require?

Answer 20

Long courses of antibiotics, generally 6 weeks IV, but in some cases months of oral abx may also be needed (particularly for prosth. joint infections)

• Surgery may also be needed to remove sequestra or prostheses (when abx alone fail)

Question 21

What antibiotic appears to be particularly useful in treating bioflm organisms?

Answer 21

Rifampin - markedly improved sucess in therapy of prosthetic joint infections (but only for staphylococci and only those that are susceptible to it).

Question 22

Antibiotic treatment is only useful when…?

Answer 22

If the bone is covered in tissue - otherwise new organisms can continuously invade the bone.