uka failure mechanisms vs tkr | Prosthesis | Knee

252 subjects with aseptic implant failure and 79 with prosthetic joint infection were enrolled. Sonicate fluid was not concentrated; 0.5 ml was plated on an anaerobic and aerobic sheep blood agar plate and incubated anaerobically and aerobically, respectively. This slide shows the quantity (and type) of microorganisms detected by sonicate fluid culture. Most of the prosthetic joint infection specimens yielded >100 colony forming units per plate, whereas most of the aseptic failure specimens yielded no growth or a small number of colonies. A cutoff of 5 colony-forming units of the same organism was determined to most accurately differentiate aseptic failure from infection.

aseptic failure of a knee prosthesis is not associated ..

Deep infection was the most frequent cause of failure of revision of aseptic total knee ..

prosthetic joint failure, the appearances of aseptic loosening and ..

In cases where the diagnosis of Prosthetic Joint Infection has not been established preoperatively, assessment for acute inflammation on intraoperative frozen section provides rapid intraoperative assessment for Prosthetic Joint Infection, with sensitivities of 43-100% and specificities of 77-100% (using cutoffs varying from >5 to ³10 polymorphonuclear leukocytes per high power field).

Prosthetic Joint Infection Diagnosis [Hot Topic] - Insights

The most useful pre-operative diagnostic test (where there is uncertainty) is joint aspiration for total and differential cell count and culture. Aspiration should not be performed through overlying cellulitis. A synovial fluid leukocyte count of more than 1.7x103/μl or a neutrophil percentage of more than 65% is consistent with prosthetic knee infection. Hip aspiration may require imaging guidance. A synovial fluid leukocyte count of more than 4.2x103/μl or a neutrophil percentage of more than 80% is consistent with prosthetic hip infection. These cutoffs are dramatically lower than those used to diagnose native joint infection. Synovial fluid culture has a sensitivity ranging of 56 to 75% and specificity of 95 to 100%, and to achieve ideal sensitivity and specificity should be performed by inoculation into a blood culture bottle. If an organism of questionable clinical significance is isolated, repeat synovial fluid aspiration for culture should be considered. Prior antimicrobial therapy reduces sensitivity.

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Collection of multiple periprosthetic tissue specimens for aerobic and anaerobic bacterial culture is imperative because of the poor sensitivity of a single tissue culture, and to distinguish contaminants from pathogens. It has been demonstrated that, ideally, five or six specimens should be submitted for culture. In addition to prior systemic antimicrobial therapy, cultures may be falsely negative because of leaching of antimicrobial agents from antimicrobial impregnated cement, biofilm growth on the prosthesis surface, a low number of organisms in tissue, inappropriate culture media or inadequate culture incubation time, or prolonged transport to the laboratory. Fungal and/or mycobacterial cultures may be considered, but are not routinely recommended. Since microorganisms associated with Prosthetic Joint Infection attach to the prosthesis and persist as biofilm microorganisms, obtaining a sample from the prosthesis surface is useful for microbiologic diagnosis. Vortexing combined with sonication of the implant is a simple technique that can be performed in most microbiology laboratories and has been shown to be more sensitive than and as specific as multiple periprosthetic tissue cultures for diagnosing prosthetic hip, knee and shoulder infection as well as spine implant infection, provided that an appropriate cutoff for significant results is applied. This approach is particularly helpful in patients who have received prior antimicrobial therapy. Sonication in bags is not recommended due to contamination. This slide shows an outline of the procedure that we use for implant sonication. The implant is collected in a sterilized 1-liter, straight-sided, wide-mouthed polypropylene jar and transported to the laboratory. Four hundred milliliters of Ringer’s solution is added to the container. The container is vortexed for 30 seconds and then subjected to bath sonication for 5 minutes, followed by an additional vortexing for 30 seconds. In our original study we directly plated 0.5 ml of sonicate fluid to aerobic and anaerobic sheep blood agar plates, but we now concentrate the sonicate fluid hundred-fold by centrifugation and plate 0.1 ml of concentrated sonicate fluid.

Infection after total knee replacement (IATJ) is a rare complication

The pathogenesis of Prosthetic Joint Infection involves the formation of microbial biofilms. Bacteria, typically inoculated at the time of implantation, adhere to the implant and enter into a phenotypically unique, biofilm state in which they are relatively protected from conventional antimicrobial agents and the host immune system. In this biofilm state, they grow slowly and elaborate an extracellular polymeric matrix. As mentioned, in the biofilm state, they are relatively resistant to antimicrobial agents and the host immune system. However, the immune system is attracted to the site of infection, and this can result in destruction of tissues surrounding the prosthesis and the finding, for example, of acute inflammation in periprosthetic tissues.

the diagnosis of prosthetic knee infection ..

Antimicrobial agents alone, without surgical intervention, ultimately usually fail. The quality of surgical debridement is critical. A general approach to surgical management is outlined, although different centers and surgeons may use slightly different strategies. Chronic infections require resection arthroplasty either as a one-stage, with removal and reimplantation of the prosthesis during the same surgical procedure, or a two-stage, with removal of the prosthesis and systemic antimicrobial agents with subsequent prosthesis reimplantation exchange. Patients with symptoms of prosthetic joint infection for fewer than three weeks, who present with early postoperative or hematogenous infection, and who have a well-fixed, functioning prosthesis, without a sinus tract, and with appropriate microbiology represent a select group potentially amenable to debridement and retention of the prosthesis. When unacceptable function is anticipated following surgery or the infection has been refractory to multiple surgical attempts at cure, resection arthroplasty with creation of a pseudarthrosis for hips (a Girdlestone procedure) or arthrodesis for knees may be considered. If the patient is not a surgical candidate, antimicrobial suppression may be considered; this approach is unlikely to cure infection, so antimicrobial agents are often continued indefinitely.