MSK infections

Question 1

What are the various routes by which bone and muscle get infected and the risk factors for those infections?

Answer 1

1. Open fractures (nastier organisms than closed fracture)
   - polymicrobial
   - aggressive debridement
2. Diabetes/ Vascular insufficiency (different recovery)
   - polymicrobial
   - MRI for diagnosis
   - debridement + antimicrobial
3. Haematogeneous osteomyelitis (staph aureus/streptococci, classically in PWID)
4. Sickle cell osteomyelitis (staph aureus, salmonella)
   - get bone infarction more than infection
5. Vertebral osteomyelitis (staph a., group A strep)
   - only 1/2 have a fever or raised WBC count
   - most have insidious pain/tenderness
   - do MRI or CT
   - treat: drainage of large abscesses + 6 weeks antimicrobial
6. Skeletal tuberculosis
7. Septic arthritis
8. Pyomyositis (mostly staphyloccal/viral, sometimes fungal/parasites)
9. Prosthetic joint infection (skin commensals may contribute)

Question 2

What’s the timing and rationale for the tests required to diagnose musculoskeletal infections?

Answer 2

Question 3

What are the pathogens associated with bone and muscle infection?

Answer 3

Negative culture need two days to get back

1. Staphylococcus aureus (not that virulent for bones - but still!)
   - gram +ve
   - coagulase +ve (clots plasma)
2. Staphylococcus epidermidis (not so relevant unless metaloplastic)
   - gram +ve
   - coagulase -ve

Streptococcus pyogenes - Group A Strep
Gram negatives (Important with specific situations)
Anaerobes (Important with specific situations)

Question 4

What are the treatments of infections of bone and muscle?

Answer 4

1. Debridement
   Debrided bone takes 6 weeks to be covered by vascularised soft tissue
2. Antimicrobials (adjunct to debridement)
   a) antibiotics - try to AVOID without microbiological sample [drug treatment should only be relevant if there is a clinical problem, and not positive test result]
   Flucloxacillin (better than vancomycin)
   Vancomycin
   Doxycycline (when stepping down to oral)
   Clindamycin (when stepping down to oral/doesn’t cover gram negative - but it’s 4C)
   metronidazole

Gram +ve cover:
Flucloxacillin IV for Staph (and Strep)
(Vancomycin instead of flucloxacillin of penicillin allergic)
Oral switch for gram positives is doxycycline ( bone penetration excellent. Oral Flucloxacillin has poor bone penetration)

Gram -ve cover:
Gentamicin/ Aztreonam IV - if severe
Oral Cotrimoxazole/ doxycycline if suitable for oral treatment

Anaerobes:
metronidazole

When there is pus –> source control

Question 5

Treatment for Staph Aureus

Answer 5

IV options:
Flucloxacillin (MSSA only)
Vancomycin (takes longer to function than flucloxacillin)
Teicoplanin
daptomycin

Oral options:
Doxycycline
Cotrimoxazole
Linezolid
Clindamycin
(rifampicin)

Question 6

What is orthopaedic antimicrobial prophylaxis?

Question 7

What is the antimicrobial spectra of activity?

Question 8

What are some basic principles in bone & joint infection diagnosis?

Answer 8

1. Don’t start antibiotics until you know what you’re treating
   2.

Question 9

What is technetium scan?

Question 10

What are causes of acute osteomyelitis?

Question 11

How to manage acute osteomyelitis?

Answer 11

• Let abscess out

Question 12

What is chronic osteomyelitis?

Answer 12

Causes -
An untreated bone abscess leading to more dead and dying bone (sequestrum), resulting in involucrum forming

Question 13

How is chronic osteomyelitis investigated and treated?

Question 14

What is septic arthritis?

Question 15

How to manage septic arthritis?

Question 16

What are some soft tissue infections?

Answer 16

Necrotising fasciitis (gas-forming microbes in soft tissues) - emergency!!!

Question 17

How would infected arthroplasty present?

Question 18

What is the prophylaxis for