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    How Should Surgeons Implant Articulating Antibiotic Spacers in Revision TKA?

    Dr. Jeremy Gililland, Dr. Victor Carlson, and Dr. Lucas Anderson answer ICJR’s questions about their technique for building and then implanting an articulating antibiotic spacer in the first stage of revision total knee arthroplasty.

    ICJR: What are the options for articulating antibiotic spacers used in revising an infected total knee arthroplasty (TKA)?

    Victor R. Carlson, MD: Many techniques, and variations on these techniques, have been proposed for articulating antibiotic spacers in patients undergoing 2-stage revision for a periprosthetic joint infection (PJI). The majority of these techniques have used cement molds or cemented metal components on the femoral side and cement molds or cemented all-polyethylene components on the tibial side.

    Initial cement-only techniques were hand-tailored, but more recently, silicone molds and even prefabricated cement spacers have been developed to streamline this approach. [1-4] Although effective, silicone molds and prefabricated constructs are surprisingly expensive. [5] Metal-on-polyethylene constructs provide a potentially more durable alternative without added cost compared with molded and prefabricated cement constructs. [6] Incorporation of reused autoclaved components has been described, with studies showing non-inferior outcomes and additional financial incentives. [7-9]

    Both cement-only and metal and polyethylene constructs are compatible with cemented femoral and tibial dowels, which can provide additional component stability and enhance intramedullary antibiotic delivery.

    ICJR: Are there any advantage in infection eradication or range of motion for one type of antibiotic spacer over another?

    Dr. Carlson: Although there are many studies on articulating and static spacers, the literature comparing specific articulating spacer subtypes is limited. Kalore et al [8] found no difference in infection eradication and range of motion among 15 autoclaved femoral components, 16 new femoral components, and 22 molded femoral components. Zielinski et al [10] reported equivocal eradication rates among constructs with and without dowels. In their meta-analysis evaluating 4 types of articulating spacers, Spivey et al [11] found equivocal rates of reinfection. However, patients with metal-on-polyethylene spacers demonstrated significantly higher interim range of motion and lower spacer-specific complications.

    ICJR: Do you have a preferred type of articulating antibiotic spacer? Has it changed since you began your practice?

    Jeremy M. Gililland, MD and Lucas A. Anderson, MD: In patients with intact extensor mechanisms and collateral ligaments, we use cemented all-polyethylene components with dowels for the tibia and new metal components with dowels for the femur.

    Although the basic construct has remained relatively similar, our technique has evolved to its current form over several years of practice. Specifically, our efforts to balance the knee during the first stage of revision has increased with time. This unique approach has led to high levels of patient satisfaction. In fact, a minority of our patients have elected to forego the second stage of revision given the high function, stability, and infection eradication afforded by the initial surgery. This is obviously advantageous in medically ill patients who are at high risk of complications when undergoing additional surgical procedures. We often refer to these enduring spacers as “accidental 1-stage” knees, or stage 1.5 spacers.

    ICJR: What is your technique for removing the infected components, building the articulating antibiotic spacer, and then implanting the components and spacer in the first stage of the revision procedure?

    Dr. Gililland and Dr. Anderson: Our goal during implant removal is to spare as much bone as possible. With this in mind, we use curettes, osteotomes, single- and double-sided reciprocating saws, and burrs to free the components at the cement-implant interface. When explant of the tibial component is unsuccessful, as in the case of a tibial component with a cone, we escalate to a tibial tubercle osteotomy (TTO). [12] This provides direct access to the tibial stem in addition to enhancing the entire surgical exposure, improving access to the medial and lateral tibia tray and both sides of the femoral cement-implant interface.

    Following successful implant removal and thorough debridement, which includes reaming the femoral and tibial canals and debriding gutters and posterior capsule (including potential baker’s cysts), we begin with restoration of the distal femur and proximal tibia. Using a standard extramedullary guide for the tibia and an intramedullary guide for the femur, we aim to remove as little bone as possible – often only 1 mm to 2 mm – to restore the templated mechanically aligned joint surfaces. Scar tissue, cement remnants, and osteophytes are excised from the proximal tibial, distal femur, and posterior condyles. Any osseous defects potentially requiring augments are noted.

    With the distal femoral and proximal tibial surfaces restored, attention is turned to balancing the extension and flexion gaps. We begin by placing a tensioning device in our extension gap, which provides information regarding the thickness and balance of the gap. Soft tissue releases are performed as needed to obtain the coveted rectangular extension gap. We use components with increased constraint or to a static spacer if deficient collateral ligaments are noted at this stage.

    The knee is then flexed, and the tensioner is placed to assess and balance the flexion gap. If needed, magnetic augments are placed on the large side of the gap to obtain a rectangular flexion gap. We have found that 5 mm of augmentation corrects about 3 of angulation in the flexion gap. The augments are placed on the posterior flanges of the trial CR femur to maintain the symmetric flexion gap (Figure 1). In cases of flexion-extension mismatch, distal femoral augments, in addition to the posterior femoral augments, are placed to obtain the desired extension and flexion gaps. We prefer our flexion gap to be 1 mm to 2 mm tighter than our extension gap.

    Figure 1. Trial femoral component with magnetic augments to obtain a balanced flexion gap.

    After measuring and choosing appropriately sized components that incorporate the necessary augments, we begin trialing. Adjustments in femoral component sizing and trimming of the distal femoral surfaces (anteriorly and posteriorly) are performed until the femoral trial with augments is properly seated. The tensioner is then used to measure the thickness of the gaps that will be occupied by the all-polyethylene tibia cement construct (Figure 2).

    Figure 2. Gap tensioner used to measure the thickness of the flexion and extension gaps that will be occupied by the allpolyethylene tibia cement construct.

    Following thorough irrigation with saline, povidone-iodine, Dakin’s solution, and dilute chlorhexidine, we release the tourniquet, remove outer drapes and stockinette, exposing new suction, pulse-lavage and bovie between layers of outer drapes and clean drapes and ioban beneath. We then all break scrub, rescrub, regown, and bring in a new scrub table with unused instruments. We initially prepare 2 batches of cement to create the femoral and tibial dowels, femoral augments, and the all-polyethylene tibial cement construct. We augment the underside of a 9-mm all-polyethylene tibial component to create the necessary combined thickness to fill our gap.

    We drill the stem of the tibial polyethylene with a one quarter-inch drill and thread a 9/64 Steinman pin into the tibial component prior to cement being placed on this pin to create a monoblock stemmed tibial component. The femoral dowel consist of twisted Luque wire or threaded Steinman pins coated with cement and sized to match the diameter of the previously reamed femoral canal. We do not focus on length except to make sure we have reamed adequate depth to avoid dowels getting held up proud with insertion.

    The femoral augments are molded flat to size and allowed to harden in place on the CR femoral component at the exact location and size of the previously used magnetic augments. Once these prepared components have hardened on the back table, we then prepare an additional 1 or 2 batches of cement and cement the components into place with fresh cement on the undersurface of the components and dowels (Figures 3 and 4). We cement the tibial component first. We then deliver the femur over the tibial component, place the femoral dowel, and cement the femoral component in place. Finally, we bring the knee to extension and cement the patella in place.

    Figure 3. Final spacer components, including the femoral dowel, CR femoral component with cement augmentation, and the allpolyethylene tibial component with unitized dowel and cement mantle.

    Figure 4. Radiographs with the final spacer components in place.

    ICJR: What is your “recipe” for antibiotic cement?

    Dr. Gililland and Dr. Anderson: We use 3 to 4 batches of cement mixed with appropriate antibiotics as directed by cultures. Our typical regimen includes 3.6 grams of tobramycin and 2 grams of vancomycin in each batch of non-antibiotic high-viscosity cement. We use cobalt cement, which is high viscosity and elutes antibiotic at a higher rate than low-viscosity cement. If a low-viscosity cement, such as Simplex LV, is used, the surgeon should consider adding more antibiotic than what we add. Also, adding a small amount of extra cement monomer is often useful for countering the effects of the added antibiotic powder. In cases of failed infection treatment, we add antifungal agents, such as amphotericin, to our regimen.

    Author Information

    Victor R. Carlson, MD; Lucas A. Anderson, MD; and Jeremy M. Gililland, MD, are from the Department of Orthopaedics at the University of Utah in Salt Lake City.

    Disclosures: The authors have no disclosures relevant to this article.

    References

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