KEY POINTS
■ Two-stage revision arthroplasty is the most commonly used treatment for infected total knee arthroplasty and has thus far had the best treatment results reported in the literature.
■ Alternative treatment options have been employed to attempt to shorten duration of disability, reduce the number of surgeries, reduce costs, and improve ultimate outcome.
■ These alternatives include single-stage total knee revision arthroplasty, open irrigation and debridement, and arthroscopic irrigation and debridement.
■ The alternative procedures have had some success, and evidence suggests that they may have a role when treating early infections or against certain infecting organisms. Additional research needs to be done, however, to determine their overall effectiveness and appropriateness.
Total knee arthroplasty is used to treat end-stage arthritis from myriad causes, including osteoarthritis and rheumatoid arthritis. The procedure involves reshaping the distal end of the femur, the proximal tibia, and the undersurface of the patella using an oscillating saw. Bony ends thus prepared are then resurfaced with metal components and either cemented in place or fitted together using a very tight pressfit technique. Finally, a polyethylene insert is placed into the tibial implant as an articular surface for the femoral component (Figure 1). Total knee arthroplasty allows patients with severe arthritis to walk with less pain and to improve function and activity levels.
INFECTED TOTAL KNEE ARTHOPLASTY
Total knee arthroplasty carries multiple risks, including the risk of hardware wear or failure, loosening of aseptic hardware, deep vein thrombosis, and infection. Of the small number of arthroplasty failures that do occur, infection is a frequent and costly cause. Hanssen and colleagues documented a 2.5% infection rate for 18,749 total knee arthroplasties performed at the Mayo Clinic between 1969 and 1996.1 Johnson and Bannister found a superficial infection rate of 4.9% and a deep infection rate of 5.3% after reviewing 471 arthroplasties.2 In yet another study, 35 infections occurred following 695 primary and 133 revision total knee arthroplasties, resulting in an overall infection rate of 3.6%.3 Total knee arthroplasty is becoming more common as the population continues to age. The increasing number of these procedures means that the number of infected arthroplasties will increase as well.
Staphylococci are the most common organism associated with both superficial and deep infections. Deep total joint infections are essentially cases of septic arthritis in the presence of metal arthroplasty components. The metallic components act as a nidus for bacteria, making eradication of infection more difficult than in cases of septic arthritis without the metal components. As the infection progresses, it can invade the interface between the host bone and the implant or cement fixing the implant. Such progression of infection can cause the components to loosen, a condition that can be treated only by removing the component. Additionally, infection in the implant-bone interface makes eradication by surgical and pharmacologic means more difficult and may also require component removal—not because the implants have failed but to allow the infection to be eradicated.
Risk factors for infection include rheumatoid arthritis, diabetes mellitus, a history of multiple knee surgeries, and previous infection of the same joint.2,4-6 Preoperative management of chronic medical problems, including tight glycemic control, adequate nutrition, and smoking cessation, can decrease the risk of postoperative infection.7 The use of chlorhexidine or iodine showers the night before surgery can also be beneficial.8 At the time of surgery, additional actions can be taken to decrease the risk of infection. Vince and Abdeen suggest careful incision planning in the instance of multiple previous incisions; using the most recently healed incision is recommended.7 Other factors potentially affecting the risk of wound contamination include length of surgery, amount of traffic in the operating room, preparation of the operative site, use of airflow, and dress of the operative team.1,9
Signs and symptoms of an infected arthroplasty include joint pain increased beyond normal stiffness and soreness, new onset of decreased range of motion, increased swelling or joint effusion, warmth and erythema about the affected joint, woody edema around the surgical site, and wound drainage.1,6 Systemic symptoms, although frequently absent, may include fevers, night sweats, and general malaise.
When total joint infection is suspected, early diagnosis and proper treatment increase the chances that the total joint components can be retained. Diagnostic tests should include radiography to look for loosening of the components (Figure 2), tests for inflammatory markers such as ESR and C-reactive protein (CRP), WBC count, blood cultures, and sterile aspirations of joint fluid for culture, sensitivities, and cell counts.10 Aspiration of a newly painful total joint is considered mandatory, even when other signs of infection are absent, to rule out low-grade, smoldering infection.
Joint aspiration is probably the most sensitive diagnostic test. The aspirate should be examined for color and cell count, and the fluid should be cultured. Hannsen and Rand reference a study showing that joint aspiration had a positive predictive value of 75% and a negative predictive value of 94% for diagnosing joint infection.1 Barrack and colleagues found that fluid aspirations in uninfected knees averaged fewer than 500 WBCs with less than 30% polymorphonuclear leukoctyes.11 The study also suggested that a 96% positive predictive value for infection was obtained when intra-articular aspirations showed approximately 75% polymorphonuclear leukocytes with 2,000 WBCs.11
An abnormality of joint fluid in combination with elevations in WBC count and ESR and CRP levels points to a deep intra-articular infection. The combination of diagnostic modalities assists providers in diagnosing the infected total knee arthroplasty.