Diagnostic Approach to Osteomyelitis

Initial Imaging Approach

The Infectious Diseases Society of America recommends obtaining plain radiographs of the affected bone as the initial imaging study, followed by MRI if radiographs are negative or equivocal 1, 2, 3
Plain radiographs should be examined for cortical erosion, periosteal reaction, mixed lucency and sclerosis, sequestrum, or involucrum 1, 2
If initial radiographs show classic changes suggestive of osteomyelitis, treatment for presumptive osteomyelitis should be initiated after obtaining appropriate specimens for culture 2, 3

MRI is the most accurate imaging study for defining bone infection and should be obtained when plain radiographs are negative or equivocal but clinical suspicion remains high 1, 2, 4, 3, 5
MRI findings of low signal intensity on T1 images and high signal intensity on fluid-sensitive images indicate osteomyelitis 5
Negative MRI effectively rules out osteomyelitis, characterized by maintained intramedullary fat signal and intact cortical signal 7, 5

Bone biopsy with culture and histology is the gold standard for diagnosis and should be pursued when the diagnosis remains uncertain after clinical and imaging evaluations 1, 2, 4, 3
Bone biopsy is also necessary when soft-tissue cultures are inconclusive or absent, or when infection has failed to respond to initial empirical antibiotic therapy 7, 5
The biopsy technique should involve percutaneous biopsy under fluoroscopic or CT guidance by a properly trained physician, with 2-3 specimens obtained for culture and histological analysis 1, 2

In diabetic foot infections with suspected osteomyelitis, a probe-to-bone test should be performed, and elevated inflammatory markers such as ESR should be checked 4
If an ulcer or sinus tract is present with positive MRI, wound tissue cultures should be obtained from tissues closest to the bone 7, 5
If no ulcer or sinus tract is present with positive MRI, percutaneous image-guided bone biopsy should be considered after multidisciplinary discussion 7, 5