ICL 8.11: Bone and Joint Infection

Question 1

what is osteomyelitis?

Answer 1

an infection of the bone and bone marrow

infection of bone leads to destruction and new bone formation** –> you’ll form a scar that will look abnormal and you’ll see it in an x-ray

mostly bacterial, rarely fungal (candida)

leading cause of amputations in US

Question 2

what are the types of osteomyelitis?

Answer 2

1. adult vs. pediatric
2. acute vs. chronic
3. contiguous vs. hematogenous

Question 3

what are the parts of a bone during osteomyelitis?

Answer 3

there’s normal bone and in the middle there’s dead bone called sequestrum

there’s new bone formation trying to happen around the dead bone and also a sinus tract for the fluid from the dead bone to drain

Question 4

why does osteomyelitis cause amputations so often?

Answer 4

the sequestrum CANNOT be penetrated by IV or antibiotics so this is why amputations are so common; you have to cut the limb off to get rid of the dead bone

Question 5

what is hematogenous osteomyelitis?

Answer 5

contiguous osteomyelitis occurs when the microorganisms are introduced into bone through the blood –> usually due to injection drug use

in children you see it in long bones (metaphysis most commonly)

with adults, you see it in vertebrae

Question 6

what is contiguous osteomyelitis?

Answer 6

contiguous osteomyelitis occurs when the microorganisms are introduced into bone by trauma, nosocomial contamination following surgical procedure and extension from adjacent soft tissue infection

young individuals = trauma, surgery

older = decubitus ulcers, infected total joint arthroplasties

diabetic foot and vascular insufficiency related

Question 7

what are the clinical manifestations of acute osteomyelitis?

Answer 7

dull pain, gradual onset over days

probably won’t see too many changes in x-rays; changes in bone will be more subtle

easier to treat

Question 8

what are the clinical manifestations of chronic osteomyelitis?

Answer 8

pain + sinus tract

harder to treat

Question 9

when should you suspect osteomyelitis?

Answer 9

1. probe to bone = when you see an opening, you should probe the wound to see if you can feel the bone and if you can you should suspect osteomyelitis
2. chronic deep ulcers should raise suspicion of osteo
3. erythrocyte sedimentation rate of over 70 mm/h (not specific; not diagnostic)
4. abnormal x-ray result

Question 10

what things would rule out osteomyelitis?

Answer 10

1. negative MRI result - but remember, the first 2 weeks you might not see any changes so this isn’t 100%
2. WBC and platelets can be normal; sometimes bone infection aren’t accompanied by soft tissue infection so you won’t have any systemic symptoms like fever

Question 11

what do you do if a patient with osteomyelitis can’t have an MRI?

Answer 11

ex. if someone has a pacemaker

nuclear medicine studies can instead be helpful = technetium bone spa, indium or technetium tagged WBC scans

these are very sensitive but not very specific

Question 12

what does the x-ray of someone with osteomyelitis look like?

Answer 12

like a bulge in the bone = callous formation

you might possibly see a black area in the middle of the bone too which would be the sequestrum! (dead bone)

Question 13

35 year old with no medical problems suffer accidental gunshot would to the left tibia. fracture is comminuted and requires multiple surgical interventions, fasciotomy for compartment syndrome, external fixation, eventually skin graft. 4 weeks after discharge the patient present with drainage from surgical site and a fistulous tract that can be probed down to bone. he is not febrile, WBC is normal, CRP and ESR are normal. what would you do next?

Answer 13

hold antibiotics, debried the area and obtain a bone biopsy, start antibiotics postop

don’t start with broad spectrum antibiotics unless they have systemic symptoms

Question 14

how do you know which bacteria are causing an osteomyelitis infection?

Answer 14

you need a BONE biopsy!!

superficial (ulcer/sinus tract) cultures are not reliable –> the exception is if Staph aureus grown from a sinus tract, it correlates well with presence of Staph in bone

no antibiotics before culture UNLESS patient has systemic symptoms

Question 15

what bacteria often causes contiguous osteomyelitis?

Answer 15

many times polymicrobial

1. diabetic foot = S. aureus, Group B strep, Pseudomonas
2. postoperative/trauma = S aureus, coagulase negative staph

Question 16

what bacteria often causes hematogenous osteomyelitis?

Answer 16

almost always monomicrobial

staphylococci or enteric gram negatives and pseudomonas

Question 17

which bacteria often causes osteomyelitis in sickle cell patients?

Answer 17

still staph aureus but also a lot of salmonella!

like if salmonella is causing osteomyelitis, it’s probably in a sickle cell patient

Question 18

which bacteria more rarely cause osteomyelitis?

Answer 18

1. brucella

2. bartonella henselae

Question 19

what should you be worried about if a diabetic has necrosis of the foot

Answer 19

probably have coronary heart disease too if they have ischemia of the foot

antibiotics will NOT take care of this; amputation is probably the only solution

Question 20

what are the complications involved with a diabetic foot?

Answer 20

1. vascular compromise is common
2. high glycemias impair healing and infection makes diabetes difficult to control – vicious cycle
3. small wounds can become huge problems rapidly
4. infections are polymicrobial
5. debridement is frequently needed

Question 21

which bacteria should you target with a diabetic foot ulcer?

Answer 21

target Staph aureus, Group B strep and pseudomonas

Question 22

what is a charcot foot?

Answer 22

neuropathic arthropathy

it’s a condition causing weakening of the bones in the foot that can occur in people who have significant nerve damage (neuropathy); the bones are weakened enough to fracture, and with continued walking, the foot eventually changes shape = you lose the arch of your foot and the feet look like hobbit feet

fractures in the foot due to weight bearing that eventually protrude from the foot and cause wounds that look like ulcers

acute charcot foot fractures can be hard to differentiate from cellulitis and osteomyelitis because there’s a lot of swelling and maybe even fevers that could look e like cellulitis

Question 23

what is hematogenous vertebral osteomyelitis?

Answer 23

corkscrew anatomy of vessels feeding adult vertebral bone have turbulent flow which can lead to bacterial infections

fracture /trauma can predispose patients to vertebral osteomyelitis (abnormal architecture)

usually involves 2 adjacent end plates and the disc in between

lumbar > thoracic > cervical

Question 24

what is contiguous vertebral osteomyelitis?

Answer 24

more commonly due to an external cause like from a decubitus ulcer, polymicrobial and restricted to cortical bone

whenever the tissue doesn’t heal well, you have higher chance of bacteria infecting it and eventually getting to the bone too and causing osteomyelitis

rarelyyy internal source like from the aorta, esophagus, bowel

Question 25

what are the effects of vertebral osteomyelitis?

Answer 25

you can have serious neurological problems if the vertebrae are calloused and compressing on the spinal cord

Question 26

what are some of the complications of vertebral osteomyelitis?

Answer 26

1. extension of infection posteriorly:

cause cause epidural and paravertebral abscesses, meningitis

2. extension anteriorly

could lead to paravertebral, retropharyngeal, mediastinal, subphrenic retroperitoneal or psoas abscesses

empyema

3. vertebral collapse due to bone destruction
4. spinal cord infarct
5. paraplegia

Question 27

when should you be worried that vertebral osteomyelitis could also cause concurrent endocarditis?

Answer 27

1. predisposing heart condition
2. heart failure
3. positive blood cultures; especially if for staph aureus
4. infection due to gram-positive organisms

Question 28

how do you treat osteomyelitis? what tests should you do to see if things are improving?

Answer 28

1. debride/resect infected bone
2. if hardware present, remove it because the bacteria will form biofilms on the hardware that can’t be removed
3. 6-8 weeks of antibiotics (IV -> PO)
4. utility of rifampin as an adjunct; it’s NOT the main drug; it’s often used for TB but can also be used for staph

sedimentation rate and C reactive protein levels are used for monitoring progression (do not use them for diagnosis – they are neither specific nor sensitive enough!)

imaging may retain changes beyond clinical and microbiological cure (only occasionally useful for follow up)

Question 29

what is septic arthritis?

Answer 29

it’s a bacterial/fungal septic arthritis of native joint

disseminated gonococcal infection

prosthetic joint infection

Question 30

which conditions predispose you to septic arthritis?

Answer 30

Age >80 years

Diabetes mellitus

Rheumatoid arthritis

Presence of prosthetic joint

Recent joint surgery

Skin infection

Intravenous drug abuse, alcoholism

Prior intraarticular corticosteroid injection

Question 31

what are the clinical manifestations of septic arthritis?

Answer 31

1. single swollen and painful joint –> more than half = KNEE
2. warmth, redness and restricted movement
3. fevers are common

wrists, ankles, and hipsare less common

you’ll see arthritis at the symphysis pubis in professional athletes, female incontinence surgery, pelvic malignancy,

you’ll see arthritis at the sternoclavicular, costovertebral in IV drug users

<1/5 polyarticular (RA, overwhelming sepsis)

Question 32

how do you diagnose septic arthritis?

Answer 32

blood cultures are many times positive (up to 1/2)

arthrocentesis is essential

fluid should be sent for :
1. gram stain and culture

2. leukocyte count with differential (>50,000 WBC/mm3)
3. crystals exam (fresh!)

Question 33

which infectious agents can cause septic arthritis?

Answer 33

1. Gonococcus
2. Lyme – history, serology
3. TB – usually AFB stains from fluid negative
4. Fungal – indolent; negative cultures; sporotrichosis, coccidioidomycosis, candidiasis
5. Viral – polyarthritis; dx with serology; dengue fever, chikungunya, Zika virus, parvovirus, rubella

Question 34

which inflammatory conditions can cause septic arthritis?

Answer 34

1. Gout - monosodium urate crystals
2. Pseudogout - calcium pyrophosphate dihydrate (CPPD) crystals
3. Rheumatoid Arthritis
4. Reactive arthritis

Question 35

what is gonococcal arthritis?

Answer 35

patient presents with pustular skin lesions and monoarthritis

Usually <40, MSM at any age, but watch for the older sexually active patients

Synovial fluid with typical >50,000wbc/mm3

culture is low yield; you need to use a special culture to get it to even show up = Thayer-Martin media; but NAAT is sensitive

urethritis symptoms may be absent, but NAAT +

screen for other STDs

Question 36

how do you treat gonococcal arthritis?

Answer 36

treat with ceftriaxone 1g daily 7-14d AND azithromycin single dose

Question 37

what are the risk factors for gonococcal arthritis?

Answer 37

1. pregnancy
2. recent menstruation
3. C5-8 deficiencies

Question 38

how do you treat native joint septic arthritis?

Answer 38

1. empiric based on gram stain:
   if GPC treat with vancomycin

if GNR treat with cephalosporin (ceftriaxone vs ceftazidime)

if the culture is negative (NO BACTERIA) treat with vancomycin; add cephalosporin in immunocompromised host or IVDU

definitive based on cultures – 4 weeks total, IV -> PO

2. needle aspirate (repeated) vs surgical drainage

Question 39

what are the risk factors for a prosthetic joint infection?

Answer 39

1. superficial wound infection (OR 36)
2. malignancy (OR 3)
3. prior arthroplasty infection
4. prior arthroplasty
5. male
6. smoking
7. high BMI
8. diabetes

Question 40

what is the clinical presentation of an early prosthetic joint infection?

Answer 40

Early onset (<3Mo)

acquired intraop or postop wound dehiscence;

patients will present with drainage, erythema, edema, induration, pain, effusion, fever, necrosis

usually caused by S aureus, GNB, anaerobes, polymicrobial

Question 41

what is the clinical presentation of a delayed onset prosthetic joint infection?

Answer 41

3-12 months

patients usually present with indolent symptoms– pain, joint loosening, fever and WBC <50%; sinus tract

usually caused by less virulent organisms – Cutibacterium, S epidermidis, enterococci

Question 42

what is the clinical presentation of a late onset prosthetic joint infection?

Answer 42

> 12 months

usually due to hematogenous infections from distant sites of infection (vascular catheter, UTI, soft tissue)

patients present with acute symptoms of infection in a previously well functioning joint

usually caused by S. aureus, beta-streps, GNR

Question 43

what is a bacterial biofilm on a prosthetic joint replacement?

Answer 43

bacteria adhere to foreign bodies and elaborate glycocalyx

they become metabolically inactive and protected from host defenses = high resistance to antimicrobials

Question 44

how do you diagnose a biofilm on a prosthetic joint?

Answer 44

a sinus tract is highly predictive

Imaging (xray, MRI) can show loosening/lucency

nuclear scans are generally not useful

ESR and CRP are usually elevated, but nondiagnostic

fluid analysis: WBC > 3-5,000/mcl and >65% neutrophils –> fluid and tissue culture ideally obtained prior to antibiotics

multiple intraop cultures are usually sent

explant sonication

Question 45

how do you treat a biofilm on a prosthetic joint?

Answer 45

1. debridement, antibiotics and implant retention (DAIR)
   highest failure rate
   least involved surgically
   if implant is stable, oral abx options available
2. one stage revision/exchange (OSE)
   outside US
   only hips
3. two stage revision/exchange (TSE)
   explant > cement spacer > 6 weeks abx > 2 week > reimplant
   highest rate of cure

Question 46

what are the complications of a two stage revision following a biofilm formation on a prosthetic joint?

Answer 46

1. osteomyelitis

2 periprosthetic fractures during explant

3. reinfection/failure > Need for amputation or fusion (arthrodesis)

Question 47

how do you prevent infections of prosthetic joints?

Answer 47

preoperative antibiotics and sterile precautions intraop

after the surgery, no antibiotics for dental, urologic or GI procedures