Abstract
A “two-stage exchange” remains the gold standard for treatment of the infected TKA in North America. Although there is interest in “one-stage exchange” this technique is not as familiar to many US surgeons and it is unclear if the reported results of Europe can be translated to North American practice. Specific concerns include the “radicalness” of the debridement required (which oftentimes includes the collateral ligaments, hence the popularity of hinged implants where this approach is common) and the use of fully cemented stems, which are extremely difficulty to remove if infection recurs. Thus while the idea of a one stage exchange is attractive to many North American surgeons, careful study will be required to determine if success can be achieved with a more “conservative” debridement and the use of cementless stems which are preferred by some surgeons.
The basic principles of a two-stage exchange include: Thorough debridement of all infected appearing foreign material and all cement; Placement of an interval antibiotic loaded spacer (note that the addition of antibiotics to bone cement is NOT FDA approved) – 4–6g of antibiotics per pkg of cement; typically vancomycin + tobramycin; Higher viscosity cement may be associated with higher elution; The combination of antibiotics also leads to higher elution.
Antibiotic spacers can be “articulating” or “static”. Potential advantages of an articulating spacer include greater patient comfort and an easier approach at the second stage exchange as soft tissue tension and range of motion is maintained. However, these spacers are oftentimes more costly and can break or dislocate.
The first stage is followed by approximately 6 weeks of organism specific IV antibiotics. An interdisciplinary approach with an infectious disease specialist, internal medicine and a nutritionist optimises outcomes.
Our protocol then includes weekly ESR and CRP to monitor their trend. These labs are re-checked two weeks after cessation of antibiotics to ensure the trend has not changed. The knee is routinely aspirated at this time point and the fluid obtained sent for a synovial fluid WBC count with differential and cultures (although the value of such cultures is controversial). We have found that while the ESR and CRP are significantly lower than prior to removal of the infected implant, they often times DO NOT normalise and there is no specific cut-off value that predicts persistent infection.
