Wound infection criteria
The detection of microorganisms in a wound does not in itself indicate the development of an infection. Bacteria may simply be present on the wound surface (contamination) or multiplying without tissue damage (colonization), especially if the regeneration process is actively underway.
The clinical picture is always the main guide for the physician. A microorganism is recognized as the causative agent of infection only when local signs of inflammation are present in the wound area:
- hyperemia (redness);
- local tissue edema;
- pain syndrome.
Implant-associated infections
The diagnosis of infections associated with the installation of prostheses (periprosthetic joint infection — PJI) or osteosynthesis structures (fracture-related infection — FRI) is complicated by the fact that specific symptoms are often absent, especially in a chronic course. In immunocompromised patients, clinical manifestations may be completely masked.
Clinical presentation The main signal requiring attention in PJI is pain in the area of the prosthetic joint. This is the most sensitive sign, which may be the only one. In medical practice, the rule applies: any pain in a joint with an implant (especially in the first years after surgery) should be considered an infection until proven otherwise. In the early postoperative period, the only symptom may be prolonged fluid discharge from the wound. An acute process is accompanied by classic signs: pain, swelling, redness, and elevated local and general temperature. In advanced infection, fistulas, necrosis, and purulent discharge appear.
Examination algorithm
- Examination, medical history, blood test, and X-ray.
- Puncture (in rare cases, biopsy) of the suspected suppuration focus.
In FRI, a culture study of wound discharge is performed. When PJI is suspected, cytological examination of synovial fluid is added to the microbiological culture. Important limitation: cytology of joint fluid is not recommended in the first six weeks after endoprosthesis placement, as leukocyte counts during this period yield false results.
Methods for obtaining and evaluating material
For laboratory and visual analysis, the contents of cavities or joints are obtained using a puncture — the insertion of a needle through intact tissues.
When excess fluid accumulates in the joint (hydrarthrosis), visual evaluation of the punctate provides valuable diagnostic information:
- clear straw-yellow fluid — normal;
- blood (hemarthrosis) — may indicate trauma (admixture of synovial fluid indicates its chronicity), and the presence of fat droplets is an indirect sign of an intra-articular fracture;
- turbid fluid with flakes — a sign of infection or inflammation;
- pus — purulent arthritis.
The obtained punctate is sent for cytological, laboratory, and microbiological (culture) examinations. This allows confirmation of suppuration, identification of specific infections (tuberculosis, gonorrhea), and assessment of the biochemical composition.
For definitive morphological confirmation of the diagnosis, a biopsy of tissues (skin, mucous membranes, wound edges) or intraoperative material collection is used.
Additional instrumental methods
Methods such as MRI and electromyography (EMG) are auxiliary in nature.
- MRI has several limitations: the study is contraindicated in patients with pacemakers or vascular clips. The presence of metal implants distorts the magnetic signal, creating "voids" in the image.
- EMG and electroneuromyography (ENMG) use surface or needle electrodes to assess the bioelectrical activity of muscles and nerves. This helps identify innervation disorders, causes of muscle atrophy, and evaluate patient recovery.
Class and exam questions
Is the presence of bacteria in a wound proof of infection?
No. Without local clinical symptoms (pain, swelling, hyperemia), the isolation of bacteria indicates only colonization or contamination of the wound.
Why is synovial fluid cytology not performed immediately after arthroplasty?
During the first six weeks after surgery, the leukocyte count in the punctate yields unreliable results.
Which symptom is most important when periprosthetic infection is suspected?
Pain in the area of the prosthetic joint. It may be the only sign of the infectious process.
What does the appearance of turbid synovial fluid during a puncture indicate?
Normally, the fluid is clear. Turbidity and the presence of flakes indicate the development of an infectious-inflammatory process.
What else to study on this topic
- Pathogenesis of fistulous tract formation in chronic infection
- Features of interpreting cytological smears from infected wounds
- Differential diagnosis of hemarthrosis and purulent arthritis
- Impact of immunosuppression on the cellular composition of wound exudate
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