bone and joint infections

Question 1

most common causative organism

Answer 1

of osteomyelitis (particularly that acquired by hematogenous spead) and septic arthritis: S. aureus***

Question 2

importance of culture and suscepibility testing

Answer 2

Culture and susceptibility data are essential to guide antimicrobial treatment of osteomyelitis and septic arthritis
joint aspiration and examination of synovial fluid are extremely important to elavuate the possibility of septic arthritis

Question 3

most important treatment modality of acute osteomyelitis

Answer 3

administration of appropriate antibiotics in adequate doses for a sufficient length of time - must be bactericidal
antibiotics are usually given in high doses so that adequate antimicrobial conc are reached within infected bone and joints

Question 4

standard treatment duration of osteomyelitis

Answer 4

standard duration of antimicrobial treatment for acute osteomyelitis is 4-6 weeks***

Question 5

when can oral anitbiotics be used in osteomyelitis?

Answer 5

to complete a parenteral regimen in:
-children who have had a good clinical response to IV antibiotics
-adults without* DM or PVD
organism must be susceptible to oral antibiotic
suitable oral antibiotic must be available
adherence must be ensured

Question 6

3 most important therapeutic approached to the management of septic arthritis

Answer 6

appropriate antibiotics
joint drainage
joint rest

Question 7

periosteum

Answer 7

fibrous, cellular envelope surrounding the bone

Question 8

epiphysis and diapysis are separated by the

Answer 8

epiphyseal growth plate - a rapidly growing are of bone with many blood vessels

Question 9

bone blood vessels

Answer 9

they supply bone tissue and are predominantly located in the epiphysis and metaphysis

• nutrient arteries enter bone on metaphyseal side of epiphyseal growth plate and lead to cappillaries that form sharp loops within the growth plate
• cappillaries lead to large sinusoidal veins that exit the metaphysis
• blood flow is slowed considerably - infection possible with bacterial colonization

Question 10

osteomyelitis overview

Answer 10

definition: purulent inflammation of the bone marrow and surrounding bone associated with an infection, caused by bacteria, fungi, mycobacteria
may occur in any bone
can affect all age groups
classified by route that infecting organism reaches the bone - hematogenous spread, contiguous spread, vascular insufficiency

Question 11

hematogenous spread

Answer 11

pathogen reaches the bone via the bloodstream**
risk factor: transient or persistent bacteremia, sickle cell disease (slow moving blood)
typically involves metaphysis of rapidly growing long bones* (femur, tibia, humerus, fibula) in children and vertebrae* (lumbar, thoracic) in adults
predominantly a diesease of children (1-end of growth) and adults over 50
usually caused by a single organism - S. aureus, gram-negative bacilli
-acute infection process (inflammation, edema, small vessel thrombosis) increases bone pressure - compromises blood flow - necrosis
cytokine release promote osteoclast activity - reduces bone integrity
elevated pressure and necrosis cause fragmentation of diseased bone from healthy bone (sequstrum)
continued spread of infection to outer layers of bone and soft tissue - formation of abscess and draining sinus tracts (hole in done where infection leaks out)

Question 12

contiguous spread

Answer 12

pathogen reaches the bone from an adjacent soft tissue infection** or direct inoculation during trauma, puncture wounds, surgery
usual age of onset over 40 years
site of infection: femur, tibia, skull, mandible
risk factors: srugery, trauma, cellulitis, joint prosthesis or other orthopedic implants
usually polymicrobial - S. aureus, gram-neg bacilli, anaerobes

Question 13

vascular insufficiency

Answer 13

subset of contiguous spread - infection develops as an extension of existing localized infections
usual age of onset over 40 years, elderly
site: bones of feet and toes
risk factors: DM or PVD
polymicrobial: S. aureus, coag-negative staph, strep, gram-neg bacilli, anaerobes

Question 14

osteomyeletis - bacteriology

Answer 14

S AUREUS!!! - neonates, children, adults, post-surgery
diabetes - polymicrobial
sickle cell disease - salmonella*, s. aureus
IV drug uses - GNB (esp. P aeruginosa)

Question 15

acute osteomyelitis sxs

Answer 15

sxs for few days to few weeks
abrupt onset of fever, localized pain, tenderness and swelling, decreased range of motion
if hematogenous, patients may also have chills, malaise, myalgias
vetebral - localized back pain, tenderness, fever, night sweats, weight less, neurologic sxs

Question 16

chronic osteomyelitis sxs

Answer 16

sxs present for several weeks, relapsing or unresponsive infection
pain, exudative drainage, sinus tract formation, decreased ROM

Question 17

clinical osteomyelitis diagnosis

Answer 17

evidence of clinical s/sxs of infections

Question 18

laboratory osteomyelitis diagnosis

Answer 18

elevated WBC count, ESR, CRP
important to establish bacteriologic diagnosis by culture* or infected bone and blood: bone aspiration, biopsy, surgical debridement, gram stain, if abscess present - drain, gram stain and culture, aerobic and anaerobic cultures

Question 19

radiologic osteomyelitis diagnosis

Answer 19

X-rays - soft tissue swelling, periosteal thickening or elevation, bone destruction seen 10-14 days after onset of infection (over 50% of matrix must be destroyed before detected)
CT or MRI*** (standard of care) - presence of hardware may preclude use of MRI
nuclear bone scan

Question 20

osteomyelitis treatment overview

Answer 20

goals: resolution of the infection, prevention of long-term sequelae
best prognsis in acute osteomyelitis - over 80% cute rates with surgery and appropriate antibiotics for 4-6 weeks
chronic - dead bone and necrotic material act as bacterial reservoir, surgical debridement and prolonged antibiotics required
most adults require a combo of medical and surgical therapy for a successful treatment
prompt antimicrobial therapy is necessary to limit bone destruction, mitigate need for surgery, prevent chronic infection, disruption of longitudinal bone growth and angular deformity of the bone
antibiotic choice depends on the most likely pathogens, results of bone culture and susceptibility testing, bone penetration, allergies, etc
high-dose parerenteral antibiotics are typically utilized to ensure adequate bone conc

Question 21

newborn osteomyelitis empiric treatment

Answer 21

nafcillin or oxacillin 50-150 mg/kg/day IV + cefotaxime 100-200 mg/kg/day IV
NEVER give ceftriaxine - highly protein bound - brain damage

Question 22

children under 5 osteomyelitis empiric treatment

Answer 22

If vaccinated with HBI: nafcillin 150-200 mg/kg/day IV OR cefazolin 100 mg/kg/day
If not vaccinated with HIB: cefotaxime 100-200 mg/kg/days IV

Question 23

children over 5 osteomyelitis empiric treatment

Answer 23

nafcillin 150-200 mg/kg/day IV
cefazolin 100 mg/kg/day IV
If allergic: vanc, clind, linezolid

Question 24

adult osteomyelitis empiric treatment

Answer 24

nafcillin 2 g IV q4h

cefazolin 2 g IV q8h

Question 25

IV drug use osteomyelitis empiric treatment

Answer 25

cefepime or ceftazidime 2 g IV q8h

ciprofloxacin 750 mg PO q12h

Question 26

post-op or post-trauma osteomyelitis empiric treatment

Answer 26

pip/tazo 4.5 g q6-8h
cefepime 2 g q8h
meropenem 1 g q8h
add vanc if MRSA is suspect

Question 27

patients with vascular insufficiency osteomyelitis empiric treatment

Answer 27

pip/tazo 4.5 g IV q6-8h
meropenem 1 g q8h
B-lactam or FQ + metronidazole
add vanc if MRSA suspected

Question 28

osteomyelitis directed therapy - s. aureus

Answer 28

nafcillin 2 g IV q4h
cefazolin 2 g q8h
If severe allergy: vanc 15-20 mg/kg IV q12h or clindamycin 900 mg IV q8h
if MRSA: vancomycin 15-20 mg/kg IV q12h or daptomycin 6-8 mg/kg/day IV q24h

Question 29

osteomyelitis directed therapy - streptococci (pen susc)

Answer 29

aq pen G 20-24 million units IV continuous or divided q4h

ceftriaxone 1-2 g IV q24h

Question 30

osteomyelitis directed therapy - enterococci or streptococci with pen MIC over 0.5

Answer 30

aq pen G 20-24 million units IV cont of divided q4h
ampicillin 12 g IV cont of divided q4h
if severe allergy or Amp-R:
vanc
optional gent 1 mg/kg IV/IM q8h for first 1-2 weeks

Question 31

osteomyelitis directed therapy - GNB

Answer 31

ceftriaxone 102 g IV q24h

cipro 50 mg PO q12h

Question 32

osteomyelitis directed therapy - P. aeruginosa

Answer 32

cefepime 2 g IV q8-12h

cipro 750 mg PO q12h

Question 33

osteomyelitis directed therapy polymicrobial

Answer 33

meropenem 1 g q8h
ertapenem 1 g IV q24h
pip/tazo 4.5 g q6-8h

Question 34

duration of osteomyelitis treatment

Answer 34

at least 4-6 weeks***
duration will vary depending on clinical response to therapy
duration is often longer in patients with vascular insufficiency, chronic osteomyelitis or prosthetic devices
patients may receive enitre course of therapy IV

Question 35

osteomyelitis - switching patients to oral therapy

Answer 35

patients may be switched IF:

• response to initial parenteral therapy
• oral agent achieves adequate serum and bone conc
• patient has adequate blood flow to site of infection
• compliance can be ensured
• favorable SE profile

Question 36

oral antibiotic options for osteomyelitis

Answer 36

MSSA: dicloxacillin, amox/clav, cephalexin, cefadroxil, clinda
MRSA: linezolid
-thrombocytopenia, peripheral neuropathy with long-term use
enterobacteriaceae: FQs
-tendonitis, tendon rupture with long term use
-patients over 60 years, kindey, heart lung transplant recipients, CS use
-drug interactions

Question 37

septic arthritis overview

Answer 37

inflammatory reaction withing the synovial membrane, synovial fluid, articular cartilage and joint space caused by the presence of a microorganism (bacteria, virus, fungus)
may affect single or multiple joints
may affect any joint
bacterial - a rheumatologic emergency due to potential for rapid joint destruction and irreversible loss of function d/t host inflammatory response to infection

Question 38

septic arthritis - microbiology

Answer 38

neonates - S. aureus
children - S. aureus
adults 15-40 - N. gonorrhoeae
adults overall, RA, diabetes, malignancy, immuno comp, IV drug - S. aureus!

Question 39

septic arthritis clinical presentation

Answer 39

monoarticular in 80-90% of cases
knee - most common site of infection in adults; hip most common in children
poly articular in 10-20% of cases - RX, immunosuppress, prolonged bacteremia, usually S. aureus
joint pain, decreased ROM, inflammation, swelling, erythma, warmth, fever, chills

Question 40

gonococcal arthritis

Answer 40

4 times more common in women
increased risk of dissemination during menstruation, preg, and postpartum
classic triad: dermatitis, tenosynovitis, polyarthralgia
severe joint pain, fever, chills, malaise
gram stain of synovial flui - gram neg diplococci

Question 41

septic arthritis - diagnosis

Answer 41

clinical - s/sxs
lab - inc peripheral WBC (over 50,000), ESR, CRP
arthrocentesis of affected joint
-purulent, low viscosity synovial fluid w inc PNMs
-decreased synovial glucose, inc protein and LDH
gram stain and culture of synovial fluid
blood cultures
radiology - xrays, CT, MRI

Question 42

septic arthritis treatment overview

Answer 42

prompt joint drainage and antibiotic therapy to limit articular destruction
no randomized, controlled, clinical studied have evaluated therapy for septic arthritis
initial antibiotic selection is based on gram stain of synovial fluid and most likely infecting pathogen from clinical pres
once organism identified and susceptibility known, direct therapy to causative pathogen
duration of therapy depends on organism and patient response (S. aureus - 4 weeks)

Question 43

septic arthritis - empiric therapy

Answer 43

gram-positive cocci - vanc 15-20 mg/kg q8-12h
gram negative cocci - ceftriaxone 1g q24h
gram negative bacilli: cefepime, pip/tazo, meropenem; if severe allergy: aztreonam, cipro, levo
gram-stain negative:
VANC** PLUS
-ceftazidime OR
-FQ (cipro, levo) OR
-AG (tob or gent)

Question 44

prosthetic joint infection overview

Answer 44

definition: infection occuring in prosthetic joint
presentation: sinus tract or persistent wound drainage over a joint prosthesis, pain (acute or chronic), prosthesis becomes loose

Question 45

prosthetic joint infection - diagnosis

Answer 45

history and exam, Xray, ESR, CRP, blood cultures, arthrocentesis (cell count, differential, aerobic and anaerobic culture), intraoperative histopathological exam of periprosthetic tissue samples

Question 46

prosthetic joint infection - treatment

Answer 46

antibiotic therapy should be targeted to the common causative organisms: staph (MSSA and MRSA), strep, enterococci, pseudomonas, enterobacteriaceae
duration: 4-6 weeks IV therapy followed by 3-6 months of PO therapy