Session IV: Salvage of the Infected Total Knee Replacement Infection: The Problem

Deep infection occurring in a total knee replacement is one of the most devastating complications of an otherwise highly successful operation. Infection rates have been reported in approximately 1% to 2% or somewhat less for patients having total knee replacement for osteoarthritis to more than 4% for patients having knee replacement for rheumatoid arthritis. ² It is important for the patient and the surgeon to be aware of this potentially devastating complication, to identify risk factors, and to be aware of the importance of early diagnosis and subsequent treatment.

Although many risk factors have been reported that increase the rate of infection in total knee replacement, perhaps the most significant are related to the operating room environment. This, of course, is something that the surgeon can control through the use of antibiotic prophylaxis, iodoform-impregnated adherent drapes, careful attention to wound closure, the avoidance of hematoma formation through careful intraoperative technique, and the use of drains. ¹

Infection complicating total knee replacement can occur early (within the first 3 months) or later (after 3 months). Frequently, early infections are associated with persistent hematoma formation and drainage and occur in patients who have difficulty regaining range of motion. These patients will present with some drainage of the wound and it is tempting for the clinician simply to give the patient oral antibiotics with the expectation that the symptoms will subside. Regrettably, that does not always occur and it is important to treat wound healing problems and/or persistent draining hematomas after a primary total knee replacement aggressively by thoroughly lavaging the knee and doing a careful soft tissue repair.

The most common presentation of infection complicating total knee replacement occurs late and the patient presents clinically with persisting pain, frequently at rest or at night. The pain is different from that which is seen with mechanical loosening and usually is not aggravated with weightbearing. The wound may appear fine or it may appear somewhat indurated. The knee may have a woody feeling associated with it. Diagnosis of late infection is made best with a careful history and physical examination and an aspiration of the knee. Laboratory tests, including complete blood count, sedimentation rate, and C-reactive protein are important. It is rare to have an elevated leukocyte count in patients with delayed or late infection. An elevated sedimentation rate, however, is very common as is an elevated C-reactive protein. Neither of these tests is diagnostic. Nuclear imaging can be done, but in the current authors’ experience rarely is of any use. The key to the diagnosis is needle aspiration, which probably will show a leukocyte count in the synovial fluid greater than 25,000 with a predominance of polymorphonuclear leukocytes. The culture of the fluid may show a positive organism. ¹

Plain radiographs may or may not reveal abnormalities at the interfaces in patients with late infection. It is important for the surgeon to be able to review serial radiographs and to carefully inspect the interface on several views to see whether there is evidence of a radiolucent line or change in position of the implant.

The treatment of the infected total knee replacement is complex and depends on numerous variables including the timing of the infection (early or late), the time that has lapsed between the knee replacement and the diagnosis of infection, the bacteriology, a stable or a loose implant, and soft tissue envelope around the knee. Other patient variables need to be considered including age, weight, expectations, underlying host or disease factors.

The treatment options would include debridement with prosthetic retention (open or arthroscopic), two-stage revision total knee replacement, arthrodesis, or chronic antibiotic suppression.

If an infection is diagnosed within the first 3 months and the prosthesis is solid in an otherwise healthy patient, it probably is reasonable for the surgeon to do a thorough debridement of the knee with removal of the spacer at the time and carefully lavaging and debriding the entire knee with replacement of the spacer. ² This approach is not always successful and is time dependent. If this approach is done within the first month, the chances of success are as high as 70%. However, if it is delayed more than 3 months, the chances of success probably are approximately 50%. ² To some extent, the pathogen involved needs to be taken into account with debridement and prosthesis retention. If the pathogen is gram-positive and if it is sensitive to traditional antibiotics that are not neurotoxic or nephrotoxic, the success rate is higher. However, if the organism is not particularly sensitive or if the organism requires the prolonged administration of neurotoxic or nephrotoxic antibiotics, perhaps a more aggressive approach (two-stage revision) should be considered.

The most common technique of treating chronic infection complicating total knee replacement is a two-stage revision total knee replacement. ^3–5 At the first stage, the implant is removed. This operative procedure is combined with careful and meticulous debridement of the synovium and all infected tissue within the knee (soft tissue or bone). Once the debridement is complete, the surgeon has two choices, including the use of an articulating spacer or a nonarticulating spacer (polymethylmethacrylate puck). The articulating spacer has the advantage of maintaining some motion in the knee and allowing for an easier exposure at the time of reimplantation. This technique (articulated spacer) is the current author’s preferred technique. ³ Alternatively, the surgeon can insert a methylmethacrylate puck with the knee in extension. If this is to be used, care must be taken to ensure that the puck does not move posteriorly or anteriorly because movement can cause pressure on other structures, including the wound. If a puck alone is used, it is necessary to do a more extensile exposure at the time of revision to regain an adequate flexion space.

After the debridement procedure, the patient typically is treated with intravenous antibiotics for 6 weeks. The antibiotics are stopped for 2 weeks and the knee is reaspirated. Assuming the cell count is normal and the knee is sterile, it would be the author’s practice to do the second-stage reimplantation any time after 8 weeks. If an articulated spacer has been used, this is a relatively easy revision. The knee is exposed and balanced in the usual fashion, bone defects are treated, stems are used, and the appropriate constraint is chosen. The results of revision total knee replacement with the two-stage procedure described, generally are good with a successful outcome being reported in approximately 90% of knees. ⁵ However, if the direct exchange technique is used with antibiotic-impregnated cement at the time, a successful outcome will occur approximately 75% of the time.

This session on the salvage of the infected total knee addresses many of these issues in detail including one-stage versus two-stage reimplantation, the role of fusion, and bacteriology.