Treatment of infected TKA is complex, expensive, requires more surgical and inpatient time than non-infected revision TKA, and is more prone to failure. The goal of treatment is eradication of the infection and maintenance of a pain-free, functional joint [27
Treatment options include irrigation and debridement with component retention (with or without polyethylene exchange), one-stage or two-stage exchange, antibiotic suppression, resection arthroplasty and rarely arthrodesis or amputation.
Irrigation and debridement with component retention
(with or without polyethylene exchange), is suitable for selective cases where infection occurs within the first 4-6 weeks of primary TKA or in the setting of acute hematogenous Gram positive infection with stable implants [28
]. Polyethylene liner exchange is preferred as it allows better debridement of the posterior synovium and eliminates biofilm on the polyethylene [30
]. Success of open debridement with polyethylene exchange is limited (23 to 28% success rate) by persistence of organisms on retained implants, cement and dead bone [31
]. Factors associated with success include early debridement, absence of sinus formation, multiple debridements rather than a single debridement, gram positive infection, and use of 4-6 weeks of sensitive systemic antibiotics [32
arthroplasty, first described by Insall, has been the most successful treatment alterantive for infected total knee arthroplaty (91% success rate for eradicating infection) [35
]. The first stage involves removal of all total knee components and cement, thorough debridement and irrigation followed by implantation of an antibiotic cement depot in the joint. The antibiotic cement depot releases antibiotics locally at high concentrations helping to eradicate the infection. This is supplemented by intravenous antibiotics per sensitivity for six to eight week period. If there are no clinical signs of infection and the sedimentation rate and CRP levels are declining, a decision for second stage reimplantation is made. A more extensile approach like quadriceps snip, VY-quadricepsplasty or tibial tubercle osteotomy may be necessary because of scarring between stages [36
]. The second stage involves removal of the cement depot, thorough debridement and irrigation and implantation of appropriate new total knee components with antibiotic-impregnated cement.
Use of antibiotic-impregnated cement has greatly improved the chances of success in treatment of infected arthroplasties [37
]. Antibiotics suitable for this purpose should be heat- stable, broad-spectrum, bactericidal at low concentrations, at low risk of allergy /delayed hypersensitivity, and available in powder form with low serum binding, which facilitates release from the spacer at high concentrations for prolonged periods. Antibiotics in common usage for this purpose are gentamycin, vancomycin, tobramycin and cefuroxime.
Antibiotic elution from PMMA depends on the antibiotic dose, the combination of antibiotics used, and the type of cement [38
]. The recommended doses of antibiotics are 2-5 times higher for therapeutic use than for prophylactic use [27
]. Most antibiotics have a high initial release followed by a reduced, constant, elution over the next several days.
A higher dose of gentamicin or tobramycin will increase the amount of antibiotic initially released and prolong the duration of the bactericidal level of the antibiotic. However, higher doses of vancomycin may not increase the in vivo
elution characteristics [39
]. Tobramycin may synergistically increase the release of vancomycin in the cement mix by “passive opportunism”- a phenomenon that one antibiotic dissolves, resulting in increased porosity, it allows increased elution of the other antibiotic [39
]. Tobramycin elutes better from Palacos cement (Heraceus Medical, Hanau, Germany; marketed by Zimmer Inc., Warsaw, IN) than from Simplex cement (Stryker, Kalamazoo, MI). Premixed antibiotic cements have low dose of antibiotics [41
]. Hand mixing without a vacuum results in increased porosity, which increases antibiotic elution.
There is an on-going controversy over the optimal type of antibiotic spacer to be used. Static spacers
, first described by Cohen, [42
] were historically preformed in the shape of a hockey puck that was inserted loosely in the joint space after the cement was polymerized. This technique was associated with spacer subluxation and secondary bone loss and erosion of quadriceps mechanism. This led to the development of the molded arthrodesis block. In this technique cement is placed in the knee joint in a doughy state so that it conforms to the shape of the bone ends and stabilizes the knee joint by interdigitation. Static spacers have infection eradication rates approximating 88% [43
]. Static spacers restrict knee movement between stages, distract & preserve the joint space, provide stability to the limb and give rest to the infected joint. Problems with static spacers include contracture of the extensor mechanism, collateral ligament shortening, arthrofibrosis, tibial and femoral bone loss (incidence-60%) and potential difficulty with secondary exposure for reimplantation [45
maintain joint motion between stages and cause less periarticular scarring resulting in easier surgical exposure at reimplantation. They result in marginally better post-operative ROM and function as compared to static spacers, though statistical significance is not reached [49
]. Infection eradication rates with articulating spacers approximate 92% [44
Articulating spacers can be metal on polyethylene (new components or recycled components) or cement on cement. Cement on cement articulating spacers can be pre-formed or manufactured in the operating room with cement molds or can be hand-made. Articulating spacers reduce bone loss as compared to static spacers [45
]. Problems with articulating spacers include risk of cement fracture, spacer dislocation, and potential problems with wound healing [38
Cement on cement spacers
] have more surface area for antibiotic elution, though these are expensive, take more OR time and are prone to cement fracture and formation of cement debris [49
]. Preformed cement spacers
(Interspace Knee, Exactech, Gainesville, F) deliver a lower dose of single antibiotic [36
]. The prosthesis of antibiotic loaded acrylic cement (PROSTALAC) (Depuy, Warswaw, IN) includes a bicompartmental metal femoral component articulating with a polyethylene tibial component. This has a 91% infection eradication rate but has not yet been approved by the US Food and Drug administration [53
]. Metal on polyethylene spacers
] use a new or recycled femoral component and polyethylene insert for articulation. This provides an inexpensive articulation that can be custom fitted to each patient. However, there is a lower surface area for antibiotic elution as compared to cement on cement spacers.
involves explantation of all total knee components, thorough debridement, copious irrigation and reimplantation of new appropriate total knee components with antibiotic impregnated cement followed by 6-12 weeks of systemic antibiotic therapy. This is primarily indicated in high morbidity patients unsuitable for multiple operations who are infected with susceptible organisms. Advantages of one-stage exchange include abbreviated recovery and decreased cost and morbidity due to avoidance of a second operation. There are few studies published with this technique with an average success rate of 81% [58
]. One of the studies with a higher (89%) success rate [59
] found that factors associated with success are absence of sinus formation, Gram positive infection, use of antibiotic cement in reimplantation and 12 weeks of antibiotic therapy. Another online publication of 1,000 septic knee revisions at the Endo-Klinik in Hamburg over the past 25 years using the one-stage revision procedure, the success rate with the one-stage revision procedure was reported to be 75% (http://www.cementinguniversity.com/centres-of-excellence/endo-klinik/technique/therapy/
alone is considered only under special circumstances because the prognosis for infection eradication is poor with only 6% success rate [60
]. It may be considered if the implant is stable, the microorganism has low virulence and is susceptible to oral antibiotics, and the patient has a high anesthesia risk [61
]. Long term antibiotic suppression has a risk of antibiotic related adverse effects and emergence of resistant bacteria [62
is suitable for low demand patients after failure of other treatments in patients with polyarticular rheumatoid arthritis. This eradicates infection at the cost of stability and function of the knee [63
is indicated for infected TKA with deficient extensor mechanism and in cases with highly resistant organisms or salvage after failed treatments. Mabry [64
] found that arthrodesis by intramedullary nailing has a union rate of 96% as compared to 67% with external fixation. However, the risk of recurrent infection associated with IM nailing is 8.3% as compared to 4.9 % with external fixation. Infection eradication rates with arthrodesis approach 94%, though the complication rate is also very high (40%) [64
Above knee amputation is considered for life-threatening systemic sepsis or persistent local infection combined with massive bone loss and intractable pain [30
]. The prognosis for amputation is poor as more than half of the patients become wheelchair-bound [65
]. Fortunately, less than 5 % of patients with TKA infections need amputation [66
]. Arthrodesis should be considered early in the treatment of persistent infection as multiple revision surgeries may ultimately require amputation [67