Periprosthetic joint injection
It is one of the major complications and etiologies of implant failure after TJA, is associated with substantial financial burden on the healthcare system and significant physical and psychological morbidity on patients.
Adherence of bacteria to the implant is the first step in pathogenesis.
Two distinguishable phases of reversible (non-specific) and irreversible (specific) attachments occur during bacterial adhesion to the surface of the implant.
The reversible attachment works based on nonspecific physical and chemical characteristics of the bacteria.Biomaterial and surrounding joint fluid also play a role in reversible adhesion of the bacteria to the implant. In contrast, irreversible adhesion depends on more specific structures and receptors.
Biofilms play an important role in pathogenesis of PJI. Biofilm is a complex structure comprised of microorganisms enveloped in macromolecules of glycocalyx and other protective structures. Attachment of bacteria to a surface involves cell-to-cell adhesion between microorganisms and the artificial surface. Evidence suggested intracellular internalization of staphylococci as a mechanism contributing to pathogenesis of PJI and resistance to treatment. According to this concept, staphylococci can invade and live inside the host cells, facilitating long term persistence of the microorganism in bone via evasion of antibiotics and immune system responses. “Small colony variant” strains are particularly skilled in invading and living inside the host cells. These strains have mutations that impair the electron transport pathway.
PJI exists when
There is a sinus tract communicating with the prosthesis or a pathogen is isolated by culture from at least two separate tissue or fluid samples obtained from the affected prosthetic joint; or
4 of the following 6 criteria exist.
Elevated serum erythrocyte sedimentation rate (ESR) and serum C-reactive protein (CRP) concentration, elevated synovial white blood cell (WBC) count, elevated synovial neutrophil percentage (PMN%), presence of purulence in the affected joint, isolation of a microorganism in one culture of periprosthetic tissue or fluid, or greater than five neutrophils per high-power field in five high-power fields observed from histologic analysis of periprosthetic tissue at ×400 magnification.
Early PJI (occurring <3 months after index surgery) usually manifests with acute joint pain, wound inflammation (warmth and erythema), joint effusion, and loss of function. Sinus tract and purulent drainage may also develop in some cases.
Chronic PJI usually presents with chronic joint pain and loosening of the prosthesis.
Culture of aspirated joint fluid and samples should be taken intraoperatively.
3 to 5 samples from various locations around the prosthesis should be taken to increase the likelihood of obtaining positive culture.
Repeating the joint fluid aspiration SR of 30 mm/hr and CRP of 10 mg/L have sensitivity of 94.3% and 91.1%, respectively. a synovial fluid WBC count >1700 cells/μL (range: 1100 to 3000 cells/μL) or a neutrophil percentage >65% (range: 64% to 80%) is highly suggestive of chronic PJI.
A frozen section is a very good “rule-in” test but has relatively low value as a “rule-out” test.
Leukocyte esterase strips, measure of inflammatory biomarkers in the synovial fluid, and Ibis T5000 universal biosensor are some of these advances.
Irrigation and debridement
Traditionally, irrigation and debridement (I and D) with exchange of the modular prosthetic components has been treatment of choice in acute postoperative and acute hematogeneous PJI.
Two-stage exchange arthroplasty is treatment of choice for PJI in the United States,
Radical synovectomy and debridement of soft tissues in conjunction with addition of postoperative systemic antibiotic administration are other treatments.
In acute PJI where an initial attempt at more conservative surgical treatment such as I and D or one-stage exchange have failed, use of subsequent two-stage exchange procedures have been indicated.
Spacers not only allow for increased joint stability, but also prevent soft tissue contraction and facilitate reimplantation procedures.Chronic antibiotic suppression alone may be reserved in those patients with immune compromise or comorbidities too significant to undergo a surgical procedure.
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