Chapter 56 - Musculoskeletal Infections and Microbiology

Question 1

what is the most common pathogen in septic arthritis in all age groups and risk categories with the exception of children <4yo?

Answer 1

staph aureus

Question 2

What two groups are at higher risk of group B strep (strep agalactiae) septic arthritis?

Answer 2

1. neonates
   2 elderly, infirm, DIABETICS

Question 3

what are the most common gram negative cocci implicated in septic arthritis?

Answer 3

N. gonorrhoeae
N. meningitidis

Question 4

what is arthritis-dermatitis syndrome?

Answer 4

triad of
1. dermatitis - small erythemtous papules that progress to pustules
2. tenosynovitis
3. migratory/additive poly-arthritis

2/2 N. gonorrhoeae infection

Question 5

Gram stain for N. gonorrhoeae

Answer 5

PMNs with intracellular gram neg diplococci

Question 6

at risk groups for GNR septic arthritis

Answer 6

1. neonates
2. IVDA
3. elderly/immunocompromised
4. diabetics

Question 7

what bugs are IVDA patients susceptible to for septic arthritis

Answer 7

1. staph is still the most common
2. pseudomonas
3. s. epi
4. serratia
5. polymicrobial

Question 8

what bacteria is most causative for osteoarticular infections in kids between 6mo-4yr

Answer 8

Kingella Kingae
- slow growing, gram negative coccobacillus
- best isolated on blood culture media
- must hold specimen for two weeks
- PCR is best way to detect
- resistant to vanc/clinda
- tx with 2nd or 3rd gen cephalosporin

Question 9

increased virulence with staph aureus is accomplished via:

Answer 9

1. Protein A secretion - inactivated IgG
2. Capsular Polysaccharide production - prevents opsonization and phagocytosis
3. biofilm production
4. PVL - panton valentine leukocidin - cytotoxin that lyses WBCs - increases DVT, PE, more common in community acquired MRSA

Question 10

Characteristic posture of infants with septic arthritis of the hip

Answer 10

flexion, abduction, external rotation

Question 11

kocher criteria

Answer 11

fever >101.3
refusal to bear weight
wbc >12k
ESR >40

if 3 are positive 93% incidence of septic arthritis
99.6% if 4/4

Question 12

what are the intra-articular physes

Answer 12

1. proximal femur
2. proximal humerus
3. proximal radius
4. distal fibula

Question 13

histopathology of acute osteomyelitis

Answer 13

replacement of fatty marrow by polymorphous field of PMNs, lymphocytes, and plasma cells

Question 14

osteomyelitis on MRI

Answer 14

dark on t1
bright on t2 and stir

Question 15

dosing for treatment of pediatric AHO

Answer 15

vancomycin 15mg/kg ever 6 hours

Question 16

pearls for use of rifampin

Answer 16

should never be used as monotherapy - rapid resistance develops
- additive therapy for MSSA and MRSA
- excellent bone penetration and bactericidal

Question 17

C.diff infection is most likely to follow what antibiotic use?

Answer 17

• gram positive, anaerobic, spore forming bacillus
• most associated with prophylactic use of cefuroxime (second generation cephalosporin)
• treat with oral vanc or fidaxomicin

Question 18

pearls with using vanc for surgical prophylaxis

Answer 18

should be given 2 hours prior to incision time 2/2 long infusion time

Question 19

what percent of the community is colonized with MRSA in their nares?

Answer 19

1%

Question 20

how to treat nares found to be colonized with MRSA

Answer 20

• mupirocin ointment x 5 days pre-op
  or
• betadine swab the morning of surgery

Question 21

indicators of malnutrition

Answer 21

serum albumin <3.5
transferrin <200
total lymphocyte count <1500
zinc ***

Question 22

independent risk factors for SSI

Answer 22

• surgery >2hrs
• hypothermia
  postoperative hyperglycemia >140
  HgbA1c >7

Question 23

each unit of allogenic transfusion increases the risk of SSI by how much?

Answer 23

9%