Implant-Associated Infection
Infection of an implant placed at surgery — biofilm-driven and reported separately.
Consensus Definition
Defined as either: (A) any other SSI classification shown to include or spread toward the implant; OR (B) involvement of an orthopedic or other implant placed during a procedure, without external superficial / deep / bone signs of infection, with clinical or imaging signs suggestive of implant loosening or infection, AND at least one supporting finding documented.
An implant is an object permanently placed during surgery that is not suture material, a vascular clip, or a staple. Supporting findings under route (B): pathogenic microorganisms cultured from deep tissue or implant specimens; histologic presence of microorganisms in deep tissue with specific staining; periprosthetic histology/cytology meeting an International Consensus Meeting minor criterion; or elevated inflammatory markers. Implant-associated infections should be reported separately from tissue infections, and combinations may be reported.
VETSSI Clinical Interpretation
Implant-associated infection is biofilm disease. Microorganisms grow adherent to the implant surface in a hydrated extracellular matrix, which makes them hard to culture and able to persist with minimal outward signs. The consensus gives it two routes in — spread from another SSI, or implant involvement without external signs — and asks for it to be reported as its own category, because lumping it with tissue infection hides the distinct biology and origin.
Why This Matters Clinically
Implant infection is the textbook 'aseptic loosening vs septic loosening' problem. Presuming loosening is mechanical when it is in fact infective leads to revision strategies that fail. Because biofilm organisms culture poorly, a negative culture is not reassurance. Reporting implant infection separately is what lets a practice see whether its orthopedic and implant program has a problem at all.
Diagnostic Criteria
Route A: an established superficial, deep, or organ/space SSI demonstrated to involve or spread toward the implant.
Route B: implant involvement WITHOUT external layer signs, WITH clinical or imaging signs of loosening or infection, PLUS one supporting finding — implant/deep-tissue culture, histologic organisms, a periprosthetic ICM minor criterion, or elevated inflammatory markers.
Report separately from tissue-layer SSI; combinations may be co-reported.
Clinical Signs
- Clinical or imaging signs of implant loosening
- Pain at the implant site
- Lameness or lack of function
- Periprosthetic lucency or osteolysis on imaging
- Elevated inflammatory markers (e.g. neutrophil count, CRP, SAA)
- Note: overt local signs of infection may be absent
Practical Clinical Examples
Progressive lameness with periprosthetic lucency, no draining wound; periprosthetic aspirate cytology meets an ICM minor criterion. Implant-associated infection via route B.
A deep SSI shown on exploration to extend to and involve the plate and screws — implant-associated infection via route A, co-reported with the deep SSI.
Indolent lameness, implant loosening on radiographs, elevated inflammatory markers, and organisms cultured from implant specimens at revision.
Diagnostic Gray Zones
Differential reasoning at the bedside. Expand for the clinical breakdown.
- Implant infection and purely mechanical loosening can produce an almost identical clinical and radiographic picture.
- Favoring infection: elevated inflammatory markers, periprosthetic cytology meeting a minor criterion, organisms on culture or histology. Favoring aseptic: a clean inflammatory profile, a mechanical history, no microbiological support — though infection can never be fully excluded on clinical grounds alone.
- Periprosthetic aspiration with cytology and culture; consider non-culture methods (PCR / nucleic acid amplification), which can detect biofilm organisms that culture misses.
- Defaulting to 'aseptic' is a recognized route to under-reporting implant infection.
Common Misclassification Scenarios
The recurring ways this definition is mis-applied — and what to do instead.
- Infection is dismissed because there is no draining wound and culture is negative.
- Revision performed without addressing infection — predictable failure of the revision.
- Implant infections vanish into an 'aseptic loosening' category; the implant program looks cleaner than it is.
- Actively work up loosening for infection — cytology, histology, imaging, markers, non-culture methods — before concluding it is mechanical.
Connected Across the System
How this definition links into the contamination pathways, protocols, and roles that produce or prevent it.
Surveillance Implications
Implant infection can present long after surgery. Record it separately with its appearance interval. Persistent or late lameness after implant surgery warrants an infection work-up, not a default mechanical explanation.
Source
Verwilghen DR, Pelosi A, Abbas M, et al. Surgical site infection definitions consensus: a first step toward improving prevention in veterinary medicine. American Journal of Veterinary Research, 2026.
DOI: 10.2460/ajvr.25.03.0099 · Open Access — CC BY-NC
Surgical site infection definitions consensus: a first step toward improving prevention in veterinary medicine.
Verwilghen DR, Pelosi A, Abbas M, et al. — American Journal of Veterinary Research, 2026
DOI: 10.2460/ajvr.25.03.0099 · Open Access — CC BY-NC
Every definition, criterion, surveillance term, and wound class on these pages derives from this expert consensus. Consensus text on each page paraphrases the paper; clinical interpretation, gray zones, and misclassification scenarios are VETSSI editorial.