Laboratory and Imaging Workup for Non-Healing Wound with Internal Fixation Device
For a patient with a non-healing wound and internal fixation device, obtain ESR and CRP immediately, followed by plain radiographs; if osteomyelitis remains uncertain, proceed to MRI, and obtain tissue cultures before starting antibiotics.
Initial Laboratory Testing
Inflammatory markers are essential for diagnosing infection in the presence of internal fixation devices:
Obtain both ESR and CRP levels as the combination provides optimal diagnostic accuracy—a normal ESR (<30 mm/hr) combined with normal CRP (<10 mg/dL) reliably excludes infection, while elevation of either marker warrants further investigation 1, 2.
ESR ≥30 mm/hr has 82% sensitivity and 85% specificity for periprosthetic infection, though it can be falsely elevated in inflammatory conditions 1.
CRP ≥10 mg/dL demonstrates superior performance with 96% sensitivity and 92% specificity for infection, making it the more reliable single marker 1.
All patients with periprosthetic infection have either an elevated ESR or CRP (or both), so normal values for both tests effectively rule out infection 1.
Obtain complete blood count with differential, though WBC count alone has limited diagnostic value for chronic infections 3, 1.
Consider procalcitonin (PCT) as an additional inflammatory marker, particularly for assessing infection severity 3.
Microbiological Sampling
Tissue cultures are critical and must be obtained before antibiotic initiation:
Send tissue specimens rather than swabs for culture, as tissue provides superior pathogen identification 3.
Obtain cultures before starting antibiotics to maximize yield 4, 3.
For wounds with exposed bone, perform probe-to-bone testing if applicable 3.
If the device requires removal, send lead-tip or hardware cultures at the time of extraction 4.
Imaging Studies
Plain radiographs are mandatory as the initial imaging modality:
Obtain plain radiographs immediately to assess for bone destruction, hardware loosening, periosteal reaction, soft tissue gas, and radio-opaque foreign bodies 3.
Plain films are required for all non-superficial infections associated with hardware 3.
MRI is the definitive imaging study when osteomyelitis diagnosis remains uncertain:
Proceed to MRI when clinical findings, plain radiographs, and inflammatory markers are inconclusive for diagnosing osteomyelitis 3.
MRI provides superior soft tissue detail and can detect early bone marrow edema before radiographic changes appear 4.
A negative MRI definitively rules out osteomyelitis and eliminates the need for bone biopsy 4.
Consider advanced imaging in specific scenarios:
For cardiac implantable electronic devices with suspected infection, obtain transesophageal echocardiography (TEE) as first-line imaging to evaluate lead-related endocarditis, independent of blood culture results 4.
FDG-PET/CT may be considered when echocardiography is inconclusive in cardiac device infections, though this applies specifically to intracardiac devices rather than orthopedic hardware 4.
Diagnostic Algorithm Integration
Use a systematic approach combining multiple modalities:
Start with ESR and CRP measurement—if both are normal, infection is effectively excluded 1, 2.
If either inflammatory marker is elevated, obtain plain radiographs and tissue cultures 3.
When osteomyelitis diagnosis remains uncertain despite elevated inflammatory markers and plain films, proceed to MRI 3.
For definitive diagnosis and antibiotic selection, bone biopsy for culture and histology may be necessary, particularly when imaging is equivocal 3.
Common Pitfalls to Avoid
Do not rely on WBC count alone—it has poor sensitivity and specificity for chronic periprosthetic infections 1.
Avoid starting antibiotics before obtaining cultures, as this significantly reduces microbiological yield 4, 3.
Do not assume a single normal inflammatory marker excludes infection—both ESR and CRP must be normal to reliably rule out infection 1.
Be aware that ESR has a longer half-life than CRP, making CRP more useful for acute infections while ESR is better for monitoring chronic conditions 5.
In diabetic patients or those with renal failure, toe pressures or toe-brachial index may be needed to assess perfusion adequacy for wound healing, though this addresses vascular rather than infectious etiology 4.