4/7 Osteomyelitis Flashcards
By what routes can organisms enter bone and cause osteomyelitis?
Organisms enter bone by the hematogenous route
or by inoculation from a contiguous focus of infection
or by a penetrating wound
what will enhance a patient’s susceptibility to infection?
- Trauma
- ischemia
- foreign bodies
(expose sites to which bacteria can bind)
what happens to bone if untreated infection becomes chronic?
Ischemic necrosis of bone
-> separation of large devascularized bone fragments (sequestra – E)
What happens when pus breaks through the bone’s cortex?
Subperiostial abscesses form, and the periosteum deposits new bone (involucrum –C) around the sequestrum
How can bacteria escape host defenses?
- Adhering to damaged bone
- entering and living in osteoblasts
- coating themselves with biofilm
65 yo woman presents with ulcer on sole of her foot, below the first MTP joint. Diabetic neuropathy. Unsure how long the ulcer has been there. What is best dx test for osteomyelitis?
- PE, vitals, pressure around the ulcer
- blood cultures, pus from ulcer
- labs: CBC, ESR, CRP
- MRI of the foot
- plain films of the foot for bony erosion or periosteal elevation.
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65 yo woman presents with ulcer on sole of her good, below the first MTP joint. Diabetic neuropathy. Unsure how long the ulcer has been there. What is best dx test for osteomyelitis?
- PE, vitals, pressure around the ulcer
- blood cultures, pus from ulcer
- labs: CBC, ESR, CRP
-MRI of the foot
-plain films of the foot for bony erosion or periosteal elevation.
What is seen on pathology of acute osteomyelitis?
organisms
neutrophils
congested or thrombosed blood vessels
What is seen on pathology of chronic osteomyelitis?
Necrotic bone (no living osteocytes)
mononuclear cells
granulation
fibrous tissue
Contiguous focus infections and those due to vascular insufficiency: most common in what age group?
Over 50y
Contiguous focus infections and those due to vascular insufficiency: what are some precipitating factors?
–Surgical interventions, orthopedic surgery (e.g., knee, hip replacements)
–History of diabetes mellitus or peripheral vascular disease
–Trauma, including open fractures
-also bedsores (decubitus ulcers)
A hematogenous infection usually involves what pattern of bones?
What is usually the source of the bacteremia?
Usually involves a single bone only
Source of bacteremia is not often apparent, may be hx of blunt trauma leading to intraosseus hematoma or vascular obstruction.
5yo at ER w leg pain. One week ago she fell off bike, & was subsequently fine. A few days later she started crying w walking. Now: temp 39, other vitals normal. Leg is painful, swollen over thigh. Hx notable for otitis media, for which she has received many courses of abx, most recently cephalexin, one month ago.
Lab results: WBCs 17000, plain film of the leg is normal. You order BCs and start abx while waiting for add’l testing. What antibiotics do you use?
- IV vancomycin to cover S aureus and strep
- IV ceftriaxone to cover S aureus, strep, and H inf.
- IV ampicillin plus gentamicin to cover streptococci, pneumococcus and E Coli
- Oral ciprofloxacin to cover staph, strep, E coli, Pasteurella multocida
- Oral cephalexin to cover S aureus and streptococci
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5yo at ER w leg pain. One week ago she fell off bike, & was subsequently fine. A few days later she started crying w walking. Now: temp 39, other vitals normal. Leg is painful, swollen over thigh. Hx notable for otitis media, for which she has received many courses of abx, most recently cephalexin, one month ago.
Lab results: WBCs 17000, plain film of the leg is normal. You order BCs and start abx while waiting for add’l testing. What antibiotics do you use?
- IV vancomycin to cover S aureus and strep (because she has been on a lot of abx, and may by this point be colonized by MRSA. Has had selection pressure from her prior abx)
- IV ceftriaxone to cover S aureus, strep, and H inf. (only covers MSSA, not MRSA)
- IV ampicillin plus gentamicin to cover streptococci, pneumococcus and E Coli (E coli not a cause of osteomyelitis in a 5 yr old)
- Oral ciprofloxacin to cover staph, strep, E coli, Pasteurella multocida (cannot give cipro to a 5 yr old)
- Oral cephalexin to cover S aureus and streptococci
**generally do not use oral abx to treat osteomyelitis
75 yo man at ED w back pain. Has been feeling unwell for weeks, w poor appetite, occasional sweats and fatigue, but no fever. Comes in now because pain is worse over the past day, and his legs feel weak. Hx notable for diverticulitis and prostatic hypertrophy, which requires intermittent self-catheterization. Retired dairy farmer, served in Vietnam in 1967.
Most urgent concern is:
- degen joint disease and spinal stenosis, for which you prescribe anti-inflammatory agents and arrange for PT
- Recurrent diverticulitis, for which you order an abdominal CT
- UTI, including pyelonephritis, for which you order UA, urine culture, and IV pyelogram
- Spinal TB, for which you do a PPD, get plain films of the spine, order a CXR
- vertebral osteomyelitis complicated by epidural abscess, for which you order an MRI of the spine
75 yo man at ED w back pain. Has been feeling unwell for weeks, w poor appetite, occasional sweats and fatigue, but no fever. Comes in now because pain is worse over the past day, and his legs feel weak. Hx notable for diverticulitis and prostatic hypertrophy, which requires intermittent self-catheterization. Retired dairy farmer, served in Vietnam in 1967.
Most urgent concern is:
- degen joint disease and spinal stenosis, for which you prescribe anti-inflammatory agents and arrange for PT
- Recurrent diverticulitis, for which you order an abdominal CT
- UTI, including pyelonephritis, for which you order UA, urine culture, and IV pyelogram
- Spinal TB, for which you do a PPD, get plain films of the spine, order a CXR (possible esp since he served overseas)
-vertebral osteomyelitis complicated by epidural abscess, for which you order an MRI of the spine (key think you worry about is epidural abscess encroacning on the spinal cord and causeing paralysis – legs feel weak -> might be the start of a cord problem.)
Are most cases of osteomyelitis Contiguous or Hematogenous in origin?
80% are contiguous (includes cases secondary to vascular insufficiency)
other 20% is hematogenous
What is the origin of the infection for osteomyelitis via contiguous focus?
what are predisposing factors for this type of osteomyelitis?
Origin: punctures, bites, surgical procedures, trauma
Predisposing factors: compound/open fractures, PVD, diabetes, orthopedic surgery
what are the common sites of infection for osteomyelitis via contiguous focus?
what is the typical patient population?
sites: feet (esp in diabetics), hands, tibia, femur
Patients: adults, esp w diabetes
what is the origin of the infection for hematogenous osteomyelitis?
what are predisposing factors?
infection originates from bloodstream
predisposing factors: bacteremia, endocarditis, sickle cell diseae, prior bone damage
what are the typical sites of infection for someone with hematogenous osteomyelitis?
what is the typical patient population?
Patients are Children, Elderly, or IVDUs
Sites for children: tibia, femur
Elderly and IVDUs: vertebrae
hematogenous osteomyelitis: where does it tend to locate within bones of children?
bacteria tend to settle in well-perfused metaphysis - especially in growing bones where they are sequestered and nourished.
Why does hematogenous osteomyelitis often to go the vertebrae of elderly and IVDUs?
Due to damage to their spines
These patients will have prior/current back pain.
Hematogenous infection: usually caused by a single pathogen, or multiple pathogens?
what is the most common pathogen?
what do we want to be sure to cover for?
caused by a single pathogen 95% of the time
caused by S aureus 50% of the time
so make sure to cover for MRSA (Ceftaroline, Vanco, Daptomycin, Linezolid, TMP/SMX -check this list!)
Hematogenous osteomyelitis:
constitutional s/s?
local s/s?
Constitutional: fever, chills, malaise, irritability, indolence (esp in adults)
Local: restricted movement, difficulty walking or bearing wt, local pain, tenderness, edema, erythema, warmth, induration
Vertebral osteomyelitis: type of contiguous or hematogenous osteomyelitis?
hematogenous.
What’s the best choice for imaging osteomyelitis?
What will it show?
MRI is best for all types (incl vertebral)
Even if osteo is seen on plain film, helpful to get an MRI: can see extent of infection and early involvement of adjacent bone.
Sens: 96%, specificity 87%
