Osteomyelitis & Septic Arthritis

what is osteomyelitis?

bone infection (caused by bacteria)

healthy bone is..

resistant to infection

- becomes susceptible to disease introduced by trauma, ischemia, or foreign body

acute osteomyelitis =

< 3 mo

chronic osteomyelitis =

> 3 mo

when should you suspect osteomyelitis?

*an ulcer that:

- is chronic or overlying bone

- fails to heal after 6 wks of tx

*"sausage toe"

*swollen foot w/ hx of ulceration

*presence of otherwise unexplained ESR/CRP

*bone is visible or probed in an ulcer base

*deep or extensive ulcer (size > 2 cm)

hematogenous osteomyelitis

bacteremic seeding of bone from distant source of infection

- spread from surrounding tissues

- bacteria trapped in small end vessels

- more frequent in children

- long bones in children & vertebrae in adults

is hematogenous osteomyelitis more common in children or adults?

children

1 multiple choice option

where is hematogenous osteomyelitis usually found in children?

long bones

1 multiple choice option

where is hematogenous osteomyelitis usually found in adults?

vertebrae

1 multiple choice option

contiguous osteomyelitis

infection introduced through pathways other than the blood

- in young adults = from trauma or surgery

- in older adults = decubitus ulcers or infected joint arthroplasties

where does contiguous osteomyelitis usually come from in young adults?

trauma or surgery

1 multiple choice option

where does contiguous osteomyelitis usually come from in older adults?

decubitus ulcers or infected joint arthroplasties

1 multiple choice option

clinical manifestations of hematogenous osteomyelitis in long bones:

- fever

- chills

- soft tissue swelling & pain

clinical manifestations of hematogenous osteomyelitis in vertebral bodies:

- back pain

- localized tenderness

- high ESR/CRP

what is the hallmark of chronic osteomyelitis?
- bacteria gets trapped in small end vessels —> bacterial infection in the bone

presence of infected or dead bone (sequestrum) that has separated from living bone

- sheath of new bone forms (involucrum) around dead bone

sequestrum

infected or dead bone that has separated from living bone

involucrum

sheath of new bone that forms around the dead bone

how is osteomyelitis diagnosed?

- ESR, CRP

- elevated WBC (lift shift)

- blood cultures + (50% of cases)

- imaging (MRI, CT, XR, or nuclear imaging)

which imaging modality is the best to detect early changes (highest sensitivity & specificity) of osteomyelitis?

MRI

3 multiple choice options

what may be seen on plain XRs w/ osteomyelitis?

- periosteal elevation

- cortical thickening

- sclerosis/irregularity of cortex

- osteolysis

- new bone formation

all changes on plain XR may take at least _______ to develop

2 wks

- sensitivity = 5% at presentation; 33% at 1 wk; 90% at 3-4 wks

what will the MRI with osteomyelitis have findings related to?

- replacement of marrow fat w/ water (secondary to edema)

- exudate

- hyperemia (excess of blood in the vessels supplying an organ)

- bone ischemia

what changes may be seen on an MRI w/ osteomyelitis?

- decreased T1 signal

- increased:

*T2 signal (edema)

*STIR (short tau inversion recovery)
- essentially it supports that there is EDEMA within the BONE MARROW

what will contrast enhance that may be helpful?

abscesses

when may nuclear imaging be helpful?

- chronic osteomyelitis

- peri-prosthetic infections

- multifocal osteomyelitis

what is an Indium WBC scan?

a type of nuclear imaging

- good for hardware infection (CT & MRIs are distorted by metal)

bone scan =

Tc-99 (technetium-99m diphosphonate bone scanning)

what do Tc-99 bone scans show?

- positive for 24 hrs after acute infection

- demonstrate a well defined focus tracer activity 1-2 hrs after the injection

- finding is correlated w/ radiotracer in same area on dynamic scans

what are the common agents of osteomyelitis in children & adults?

- staph aureus

- MRSA

- coagulase negative staph

- gram negative (e coli, pseudomonas)

what are the common agents in a diabetic foot?

often polymicrobial

- staph aureus

- strep

- gram negative (e coli, pseudomonas)

how is osteomyelitis treated?

- consult infectious disease!

- surgery (almost always indicated)

- IV abx for 6 wks after surgery

surgery (debridement of infected tissue) is almost always indicated for osteomyelitis treatment, but especially for:

- abscesses

- chronic refractory osteomyelitis

- gangrene

- sepsis

- amputation (may be necessary)

is empiric abx tx used for osteomyelitis?

no - it should typically be avoided, except in children

after osteomyelitis tx, what may be helpful in assessing response to osteomyelitis tx?

ESR & CRP

is imaging helpful in assessing response to osteomyelitis tx?

not really, can be very delayed

osteomyelitis cure =

difficult, but resolution of s/s for > 1 yr

when may non-surgical mgmt of osteomyelitis be necessary?

if there is no acceptable surgical target

- unacceptable loss of function

examples of when non-surgical mgmt may be needed:

- limb ischemia caused by unreconstructable vascular disease but patient wishes to avoid amputation

- infection is confined to the forefoot, & there is minimal soft tissue loss

- both the pt & medical provider agree that surgery carries excess risk or is other wise not appropriate or desirable

charcot foot

debilitating changes in the foot due to loss of peripheral nerve conduction (neuro-osteoarthropathy)

- cause: injury or infection

- imaging: can be non-specific due to multiple foci of inflammation & destruction

what is septic arthritis?

joint inflammation secondary to an infectious etiology

- usually bacterial, but occasionally fungal, mycobacterial, viral, or other uncommon pathogens

why is septic arthritis important?

it can cause joint destruction

what is the typical clinical presentation of septic arthritis?

- monoarticular (involving a large joint like the hip or knee; occasionally polyarticular in smaller joints like hands/feet)

- hematogenous (blood borne)

- pain

- swelling

- redness

- effusion

- fever

- warmth

- painful ROM

what is the pathophysiology of septic arthritis?

joint synovium lacks a limiting basement membrane (so, it is prone to infection from hematogenous seeding)

what may septic arthritis result from?

- direct injury

- puncture wounds

- intra-articular injections

- IV drug abuse

- IV use

risk factors for septic arthrits:

- sickle cell anemia

- HIV

- chemo

- DM

- RA

- recent joint surgery

- joint prosthesis

- previous inter-articular injections

- skin Infections

- sexual activity

most common pathogens of septic arthritis in children:

- 2-3 y/o: kingella kingae

- neonates: strep, staph aureus, n. gonorrhea

- sickle cell: salmonella

- puncture, IV use: pseudomonas

most common pathogens of septic arthritis in children AND adults:

staph aureus

most common pathogens of septic arthritis in adults:

- strep pneumo

- sickle cell: salmonella

- puncture/trauma: pseudomonas

- sexually active: n. gonorrhea

less common pathogens of septic arthritis in children and adults:

- virus (parvo, HBV, rubella, mumps, HIV)

- fungus

- b. burgdorferi (lyme)

- listeria

what is the only definitive dx of septic arthritis?

arthrocentesis (joint aspiration)

- WBC >50,000 suggests bacterial source

- cultures will confirm bacteria

if it's a prosthetic joint, a WBC of _____ suggests septic arthritis

1100

other tests that may be helpful in the dx of septic arthrits:

- CBC

- ESR

- CRP

- blood cultures

if pathogen suspected is n. gonorrhea, then get cultures from..

other areas, such as:

- oropharynx

- vagina

- cervix

- urethra

- anus

how is septic arthritis treated?

- drainage: serial aspirations, surgery, arthroscopy

- empiric abx (nafcillin, oxacillin, vancomycin)

- IV abx for 4 wks

- if prosthetic joint, aggressive debridement &/or removal of prosthetic may be indicated

what directs additional abx selection for septic arthritis tx?

- age

- risk factors

- gram stain results

if n. gonorrhea is pathogen in septic arthritis, what is the tx?

IV ceftriaxone 24-48 hrs, then transition to oral