Techniques in the treatment of the infected total knee arthroplasty

TECHNIQUES IN THE TREATMENT OF THE INFECTED TOTAL KNEE ARTHROPLASTY R A Y C. W A S I E L E W S K I ,

MS, MD

Infection of the total knee arthroplasty can be a devastating complication. Appropriate management can significantly decrease morbidity and cost. This article outlines the management of the infected total knee arthroplasty. To optimize patient outcome adherence to strict guidelines and meticulous technique will greatly improve the results. KEY WORDS: infection total knee arthroplasty, two-stage reimplantation

Infection after total knee arthroplasty (TKA) is a devastating postoperative complication. Although the general incidence of infection after primary arthroplasty is low (1% to 2%), 1-s with an estimated 500,000 replacements performed annually, greater than 5,000 infections occur per year. 4,6These infections cause significant patient morbidity and result in formidable socioeconomic costs. 3 Faced with a shrinking pool of resources, the importance of both preventing infection of implanted prostheses and effectively treating the infected arthroplasty is readily apparent. CLASSIFICATION The classification of infections around a total joint arthroplasty has evolved to reflect the success rates of the different treatment modalities. The classification that provides the best predictive ability, based on observed outcomes, involves dividing deep infections into acute and chronic categories based on the duration of symptoms. Therefore, by categorizing an arthroplasty infection into acute and chronic, the surgeon has a guideline on the necessary treatment and expected outcome for the modality chosen. Acutely infected arthroplasties are generally considered to have been symptomatic for less than 2 weeks. These infections would include those that occur in the immediate postoperative period, as well as late hematogenous infection in knees that were previously asymptomatic. Early investigators believed that arthroplasty infections that occurred long after implantation were just a delayed manifestation of intraoperative contamination. This was supported by observations that late infections were markedly reduced by improved intraoperative techniques. More recentlj6 however, late hematogenous infections with known primary sources have been shown to result in late (but acute) infection of total knee replacements. 1,7-19 Chronic infections are occasionally observed in knees

From the Universityof Ohio, Columbus, OH. Address reprint requests to Ray C. Wasielewski, MD, 410 West 10th Avenue, Room N846, Columbus, OH. Copyright © 1998 by W.B. Saunders Company 1048-6666/98/0803-0005508.00/0

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that have had a good initial result that subsequently deteriorated or more often in knees that have never really been asymptomatic since arthroplasty. These patients often give a history of having had persistent wound drainage or other wound problems (hematoma, staple abscesses, and so on). Frequentl)~ long-standing pain and tenderness and a failure to achieve motion are present in chronically infected knee replacements. On the other hand, knees that have an initially good result can become chronically infected when late hematogenous seeding goes unrecognized for greater than 2 weeks. Fortunately, the late hematogenous infection more frequently presents as an acute septic knee with the typical symptoms of severe pain (acute in onset), along with swelling and fever.

DIAGNOSIS Evaluation of the TKA with suspected sepsis can be simple or complex. 2° Any painful TKA without apparent origin (particularly if acute in onset, the patient can often state the exact time the pain began) should be worked up for possible infection. Although pain is the major presenting symptom of TKA infection cited in the majority of studies, 1 pain is also common in the TKA that is aseptically loose or mechanically unstable. Pain at rest is more common with infection, whereas the mechanical pain of loosening prevails during ambulation. The physical examination of both the aseptic loosened and septic total knee replacement can be strikingly similar with respect to effusion and tenderness. However, the knfected arthroplasty will tend to have a severely diminished and much more painful range of motion. The knee will more frequently be erythematous and warm. Laboratory analysis can be helpful in evaluating the knee when a suspicion for infection is present. The white blood cell count (WBC) may be elevated with a differential showing a predominance of immature forms (bands), and the erythrocyte sedimentation rate may be elevated. 2°-22 However, neither is particularly sensitive or specific for infection. C-reactive protein (CRP), used alone or in conjunction with erythrocyte sedimentation rate (ESR), has been shown to represent a more specific marker for infection.22,23

Operative Techniques in Orthopaedics, Vol 8, No 3 (July), 1998: pp 158-167

CRP elevations may also be a valuable postoperative marker signifying continued infection.24 Aspiration of the symptomatic TKA (under strict aseptic conditions) remains the most frequently used modality to diagnose an infected TKA. 2°,25,26 The aspirate should be sent for a Gram's stain, cell count, and appropriate cultures (with antibiotic [ATB] sensitivities). Results are very helpful if positive, 23but negative aspirates are obtained in 7% to 15% of cases that end up with a diagnosis of infection.27 Analysis of the synovial fluid by the use of polymerase chain reaction detection may optimize our ability to preoperatively detect TKA bacterial infection.28 The diagnostic s u c c e s s and accuracy are improved by the addition of intraoperative Gram's stains and cultures. However, the absence of organisms on intraoperative Gram's staining during revision arthroplasty does not confirm the absence of infection.29,3° Additionally, we also obtain multiple frozen sections to improve our ability to predict the presence of a TKA infection.3°,31,32-34 This is particularly useful to differentiate cases of aseptic versus septic loosening.30,31 Contamination of joint aspirates is common. To help address this issue, we perform repeat aspirations in all knees that have positive prerevision cultures, but have little other evidence for sepsis. If the second culture is positive, phage typing and sensitivity comparisons are made to determine if it is the same organism. If a different organism is found on cultures of the second aspirate, a third aspirate may be indicated. The expert advise of an infectious disease consultant should be obtained early in this process. Plain radiographs are frequently unreliable in diagnosing infection. Radiographic signs of bone resorption, periosteal n e w bone formation, or progressive radiolucencies are nonspecific findings that may represent chronic infection, a reaction to wear debris, or aseptic loosening. Fluoroscopically positioned radiographs to study the bone implant interface in cementless prostheses are helpful in a s s e s s i n g aseptic loosening, as but continuous radiolucencies can represent either a loose infected or aseptically loose component. Nuclear medicine s c a n s can play an important role in the diagnosis of deep infection after TKA. The three-phase bone scan is highly sensitive in detecting uncomplicated osteomyelitis but has had varying degrees of efficacy in the diagnosis of infected total joint arthroplasty, 2°,36One of the problems is that once loosening is present on radiographs, the three-phase bone scan alone is unlikely to allow one to differentiate aseptic loosening from septic loosening. To improve sensitivity and specificity, sequential technetium and gallium scanning has been used to enhance the ability to differentiate be{ween infection and loosening in the infected total joint arthroplastyY -4° Indium-Ill s c a n n i n g has been shown by some investigators to be highly sensitive and specific for infection with results superior to technetium s c a n n i n g . 39-4143 It is probably most valuable when used in conjunction with the technetium scan in which the accuracy has been reported at between 70% to 90%.39,40,42,44

THE INFECTED TOTAL KNEE ARTHROPLASTY

TREATMENT OPTIONS Antibiotics: General Concepts

Although hard data supporting this practice have yet to be established, treatment of infected TKA almost always involves the concomitant administration of 6 weeks of intravenous (IV) ATBs as recommended by Insall et al. 4s More recently, trials have been underway to determine if certain cases (acute infections and sensitive organisms) can be treated with oral ATBs that have comparable bioavailability (clindamycin, ciprofloxacin, and so on) to the IV ATBs. 46 In either case appropriate ATB selection should be based on the sensitivity of the infecting organism and the t o l e r a n c e of the patient to the resulting ATB side effects and potential complications. Central venous catheters are effective in patients requiring 6 weeks or greater of ATB therapy. These convenient portals of access for ATBs and blood draws have been shown not to contribute to potential joint reinfection (as have regular IV portals), ls,47 We consult an infectious disease expert to assist with the care of these complex patients. They help determine the ATB type and administration route and monitor levels to maximize bactericidal effects while minimizing undesirable side effects. We customize each patient's treatment regimen based on quantitative data (acute v chronic infection, organism type and sensitivities, permanent tissue sections, and so on), along with m y intraoperative findings (extent of infection, tissue integrity and bone destruction). Only when the surgeon understands the infectious disease perspective, and the patient understands the intraoperarive findings can the most appropriate and effective treatment be implemented. Although the biomaterials used for implants today are generally biologically inert, interactions with the host does impair the capacity of bactericidal cells to combat infection. 48 Causative organisms are found in glycocalyxenclosed biofilrns that were adherent to surfaces of biomaterials. 49 Furthermore, it seems that regardless of whether or not bacterial organisms are encased in slime, ATB resistance is related to surface adhesion and to the specific material of the substratum, s° This bacterial adherence may be the fundamental reasons why implants become infected and why their removal is often a prerequisite to curing an infected joint arthroplasty. Antibiotic T h e r a p y Without D e b r i d e m e n t

The treatment of the infected TKA with ATBs and no debridement has met with limited successJ A number of reports show that this technique is not effective in eradicating deep infection (Table 1). 1'15'51-53This should be reserved

TABLE 1. Results of Using ATB Therapy Alone in the Treatment of TKA Infections No. of

Follow-

Investigator

Knees

up

Successful Eradication of Infection (%)

Johnson et aP5

25 3 7

15 48 48

2/25 (8) 1/3 (33) 1/7 (14)

Grogan et al 1 Woods et al 5s

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for debilitated patients (who may not tolerate debridement) with well-fixed implants and organisms that are sensitive to oral agents. A cure is unlikely but suppression of systematic symptoms can occasionally be achieved. The risks of chronic ATB treatment must also be kept in mind. However, I usually have several patients at any given time who are on oral ATB having refused two-stage reimplantation. Generally, these are patients with low grade infection who do not significantly affect the patients" activities of daily living or medical health. I advise these patients to take (and plot) their temperatures each day and to get monthly evaluations (and eventually quarterly) of sedimentation rate and complete blood count. Any change in established baselines is an indication to proceed with surgery. This can help avoid the mortality associated with sepsis that is so worrisome in these patients. Debridement With Prosthetic Retention: I r r i g a t i o n a n d Debridement

Although some initial reports have shown good results of irrigation and debridement at relatively short follow-up, 54 in general, results of irrigation and debridement and component retention have shown high recurrence rates. 1,55-59 It should be reserved for acutely infected knees or those that occur immediately postarthroplasty when it may be reasonable to attempt aggressive multiple debridements to avoid two-stage reimplantation. 6° A prerequisite for this technique is well-fixed prosthetic components with no evidence of progressive radiolucency at the bone/cement or cement/implant interfaces. Although arthroscopic debridement is possible. 61 I prefer open debridement with complete synovectomy to optimize access to the interstices around the prosthetic components and access the bone-prosthesis and bone-cement interfaces in which bacteria and infected synovium may be harbored. Repetitive aggressive debridements, performed until negative intraoperative cultures and frozen sections are obtained, may reach these bacteria and account for this technique's improved rate of prosthesis retention. 6°,62 Failure of simple debridement correlates most closely with the duration of infection before treatment. 63 Acute infections are much more likely to be eradicated than are chronic infections (Table 2). In fact treatment performed as soon as possible (<2 days after the onset of symptoms) is associated with improved success rates compared with those with longer delays. 63 Organism virulence can also significantly affect the success rate of this modality. 66 Irrigation and debridement are less efficacious in treating infections caused by highly virulent organisms (Staphylococcus aureus, gram-negative bacteria) than by less virulent organisms. 51,65,67Results are optimized when this modality is used only in acute infections of less than 2 weeks' duration caused by infecting organisms of low virulence.55,62 Recently, an implantable ATB pump that delivers a high concentration of ATBs locally, exceeding the minimum inhibitory concentration for most organisms by 8 to 10 times, and without systemic effects, was evaluated. 67Seventeen of 20 patients treated with high local concentrations of amikacin were free of infection at 30 months. 67 This treatment, with or without IV or oral ATBs, may provide a

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TABLE 2. Results of Using ATB Therapy, Irrigation and Debridement, and Component Retention in the Treatment of TKA Infections Investigator

No. of Knees

Followup

Burger et a151

39

49

Schoifet and Morreyss

31

105

Teeny et als8

21

--

Morrey et als2 Borden and Gearens~

10 11

78 51

Wasielewski et a159

10

57

Mont* et also

14

48

Montl- et also

10

48

SuccessfulEradication of Infection (Acute/Chronic) 2/22 (9%) acute 5/17 (29%) chronic 5/15 (33%) acute 2/14 (14%) chronic 3/5 (60%) acute 3/16 (28%) chronic 8/10 (80%) acute/chronic 5/6 (83%) acute 0/5 (0%) chronic 6/8 (75%) acute 1/2 (50%) chronic 8/8 (100%) acute 2/6 (33%) chronic 7/7 (100%) acute 3/3 (33%) chronic

*Late hematogenous. 1"Earlypostarthroplasty.

reliable means of infection management in patients who have stable components on radiograph and a sensitive organism and are too debilitated or unwilling to undergo a more definitive treatment of their infected TKA. Additionally, in patients who have extensive hardware that is impossible to remove, repetitive debridement of acute infection is a rational choice to leaving the patient with an unreconstructable extremity if implant removal is performed. Debridement with Prosthetic Resection and Immediate Reimplantation: One Stage

One-stage reimplantation has been suggested as a costeffective means of treating the infected TKA. 68 Although there are recent reports of improved success with this technique, 68,69others have found short delays in reimplantation (rather than the recommended 6 weeks) to be associated with a high rate of recurrent infection.15,55,65This procedure will probably be most effective when used in patients with acute infections in which the prosthesis is found to be loose at planned irrigation and debridement. It may also have limited application in patients chronically infected with less virulent organisms, although the twostage reimplantation remains the gold standard in these cases. Probably the most important aspect of this technique is thorough debridement of the tissues. I recommend aggressive debridement through to previously undisturbed tissue. Bone should also be aggressively resected but even more extensively than would be required for two-stage reimplantation (because of the lack of an ATB spacer and 6 weeks' ATB). I recommend the use of 6 L of ATB lavage solution delivered under high pressure (pulsatile lavage) to optimize the removal of bacteria from the remaining bone and tissue interstices. The addition of organismspecific ATBs to the cement used to fix the implants to bone is recommended. At least 6 weeks and possibly 3 months of IV ATB therapy should be used. The sedimentation rate and complete blood count should be followed to assess the effectiveness of this technique.

RAY C. WASlELEWSKI

Debridement with Prosthetic Resection and Delayed Reimplantation: Two Stage Debridement with removal of the prosthesis is necessary in loose, acutely infected and chronically infected TKAs or after failed management of acutely infected TKAs. This technique involves removal of the prosthetic components, loose cement, and the cement that is intercalated into the

bone. In the worst case scenario the removal of longcemented stems requires a controlled femoral window or longitudinal femoral osteotomies (Fig 1A-D).Similarl~ a tibial tubercle osteotomy with a long anterior tibial crest component can allow for easy implant removal (with minimal tibial comminution) while assuring preservation of the patella tendon insertion (Fig 1A-D). When debriding the bone surfaces, all nonviable bone is resected while

Fig 1. A 60-year-old man presented with a grossly infected total knee replacement. (A and B) His status is post-two-stage reimplantation; he was treated two times previously for an infected knee. He was osteogenesis imperfecta. A femoral window was created to help remove the femoral stems. A tibial tubercle osteotomy was performed to help remove the tibial stem. (C and D) Despite these osteotomies, there were still cracks that propagated in this patient's very brittle bone, but they were much less severe than they would have been if the implants had been removed without these controlled osteotomies.

THE INFECTEDTOTALKNEEARTHROPLASTY

1 61

keeping bone loss to an absolute minimum. A complete synovectomy is performed and all nonvascularized and granulomatous tissue is resected. Abscess and sinus tracts are excised. Muscle flaps should be considered early to cover dysvascular regions or defects left after soft tissue and sinus tract excision. TM ATB-impregnated polymethylmethacrylate spacers or beads should be considered, in addition to IV ATBs, as a means of delivering high local antibiotic concentrations to The local the bone and surrounding soft tissues. T M concentration achieved is proportional to the surface area of the cement (ie, beads > spacer). While the systemic dose from this technique is low and without adverse effects,77,78 the eluted ATBs may act synergistically with culturedirected ATBs that are administered IV for 6 weeks. 4°,55,64,79,8° The ATB spacer may also improve the interim mechanical stability of the joint. 8I It also can be used to eliminate dead space and improve the ease of dissection and exposure at reimplantation. ~1,72,81This can help avoid the need for local rotational flap coverage at revision arthroplasty. 82 It may even improve the final range of motion achieved. 8s An actual implant surrounded by beads or coated with ATB-impregnated cement has also recently been proposed to optimize this effect.69It is unclear if these weight-bearing spacers result in improved bone stock at revision, 71,72 or bone loss and osteoporosis as we have occasionally observed. With any type of ATB spacer the potentially detrimental effects of high-dose aminoglycosides on bone turnover and loosening have not been fully elucidated. 84 Methylmethacrylate itself has been shown to decrease the chemostactic ability of polymorphonuclear leukocyte 85 and may have other adverse effects on bone and periarticular tissues. 85-88 Nonetheless, the use of ATB-impregnated cement is widespread and may be helpful in preventing recurrent infection in revision of the infected T K A . 69,81,83,89-91 At 6 weeks the ATB(s) may be stopped for a 2-day hiatus and the knee reaspirated. If negative, I reverify that a clean bed of tissue is present by Gram's stain and frozen section at the reimplantation phase of the two-stage reconstruction. If positive, ATBs are adjusted accordingly, and repeat surgical debridements should be performed until negative cultures are obtained. When necessary a salvage arthrodesis may be performed in the presence of a recalcitrant infection after prosthesis removal. 92 Once negative, reconstruction options include pseudoarthrosis (resection arthroplasty), arthrodesis, or reimplantation. Reimplantation. After

successful debridement

TABLE 3. Results of Using ATB Therapy, Irrigation and Debridement, and Component Reimplantation in the Treatment of TKA Infections Investigator

No. of Knees

Followup

Successful Eradication of Infection

Teeny et al5a Windsor et al8° Booth and Lotke71 Rosenberg et a194 Wilde and Ruth 12° Borden and Gearen55 Wasielewski et a111°

10 38 25 28 15 11 50

-96 25 48 12 -57

Bose et a189 Goldman et ai 9s

18 90

55 64

10/10 (100%) 34/38 (89%) 24/25 (96%) 28/28 (100%) 12/15 (80%) 10/11 (91%) 40/44 (91%) chronic 6/6 (100%) acute 18/18 (100%) chronic 58/64 (91%) acute/chronic

prove to be harmful, alternate therapies may be indicated. Problems of severe bone loss may be overcome by the use of a custom prosthesis or allograft bone (Fig 2), soft tissue loss by local or distant flaps 7°,82,96 and even extensor mechanism deficiencies by transfer of allograft tissue. Thus, each case must be evaluated according to the nature of the infecting organism, the patients general medical and musculoskeletal status, and the local conditions affecting the surgical reconstructability of the joint. The technique of two-stage reimplantation involves a successful initial debridement and prosthetic resection.

and pros-

resection, followed by a 6-week course of IV ATBs, reimplantation would seem to be the therapy of choice for the infected TKA (Table 3). 93 Long-term studies have shown reproducibly high success rates with a delayed exchange at 6 weeks. TM This technique has even been used subsequent to a previous failed two-stage reconstruction with favorable results. 96 Indications for reimplantation include an immunocompetent patient with adequate bone stock and soft tissues. A clear contraindication would be the situation in which sepsis cannot be eradicated. In cases in which the infecting organism is fungal or highly resistant to antimicrobial therapy or in the immunocompromised or medically debilitated patients, or in which the ATB requirements may thetic

162

Fig 2. Radiographs of a 65-year-old woman who had a failed high tibial osteotomy. She underwent a total knee replacement that subsided medially into severe varus. She had an allograft strut placed to the medial aspect of her knee, which was held in place by two threaded Steinman pins. (A and B) A 6-year follow-up. Before cementing this long stem we cemented the interface between the graft and the host bone on the inside of the canal so that when we placed this stem cement would not protrude into the host-bone graft junction. This allowed for healing of this graft. RAY C. WASIELEWSKI

After 6 weeks of appropriate ATBs and a negative preoperative aspirate, reimplantation is attempted. Frozen sections are checked to make sure the bed is clean. Bone loss and ligament laxity will often necessitate the use of a more constrained prosthesis. 97 ATB-impregnated polymethylmethacrylate seems appropriate as a method of fixation. This is of theoretical advantage in patients with preexisting immunosuppression (rheumatoid arthritis) who are at increased risk for reinfection with a different organism after a successful two-stage reimplantationS°; it also improves the odds of eliminating sepsis in patients who may still harbor organisms at the time of reimplantation. The specific techniques of reentering the pseudoarthrosis space, removing scar tissue, and performing the arthroplasty itself may require all of the surgical skill and experience that are needed for the most complex aseptic knee revision. I perform a quadriceps turndown in all cases of patella infera or whenever difficulty everting the patella threatens the insertion of the patella tendon. I use stems whenever bone loss requires the use of wedges or augments. I refrain from using bulk tibial or femoral allografts unless the entire quadricep and patella mechanism need to be replaced. (Cases of extensor mechanism incompetence are usually secondary to excessive proximal tibial bone loss,) Figure 3 and the corresponding schematics show one such case in which a proximal tibial graft with patella tendon / patella / quadriceps tendon was used. Fortunately, this worst case scenario is rarely encountered.

ARTHRODESIS After successful debridement and prosthetic resection, arthrodesis has resulted in successful eradication of infection in the majority of attempted cases (Table 4). Arthrodesis of the infected TKA is indicated in patients with knees not amendable to reimplantation. This includes patients with severe ligament laxity, paralysis, or intractable infection. Results are optimal in young patients with unilateral, monoarticular diseases who have a high functional demand. Arthrodesis is also valuable in the salvage of knees that have become reinfected after prior reimplantation for infection.98Knee fusion should be avoided in patients with ipsilatera! lower extremity (hip, ankle) or spinal arthritis, contra!ateral amputation or knee arthrodesis, or those with massive bone lOSS. 99 Many different techniques for knee fusion after infection have been evaluated, including external fixation, 89,1°°q1° intramedullary rodding, 89,98,1°°,~°2,1°3,1°7,1°8,111q13internal fixation, 1°~ and dual plating. 62,11° Although irrigation and debridement and primary arthrodesis have yielded good results,92,112 most authors use a two-stage arthrodesis in the face of infection89,1°8,~1~or a persistent draining sinus. 7° This is particularly relevant in cases in which intramedullary arthrodesis is used because the infection may disseminate if a two-stage reimplantation is not done. However, because most patients do not desire two separate operative procedures (and because the associated costs are high) many surgeons frequently choose external fixation for arthrodesis of infected total knee replacement, u4 The author has found that one-stage arthrodesis by dual plating (Fig 4) also reproducibly eradicates infection (six of six THE INFECTED TOTAL KNEE ARTHROPLASTY

Fig 3. This patient suffered a traumatic amputation of one extremity at the above-knee level after a motorcycle injury. The right extremity required open reduction internal fixation of a tibial plateau fracture that became osteomyelitic, requiring a resection and insertion of an ATB spacer. (A and B) The patient has a deficient extensor mechanism. This was revised to a tibial allograft with a patella tendon; patella and quadriceps tendon were sewn back into the patient's quadriceps tendon. (C and D) The allograft reconstruction postoperatively show some evidence of healing at a 4-month follow-up.

patients) and provides the best clinical result (five of six fused). The technique of fusion with the double plating is straight forward and performed through the same incision

163

TABLE 4. Results of Using ATB Therapy, Irrigation and Debridement, and Knee Arthrodesis for the Treatment of TKA Infections

Investigator

No. of Knees Fused for Infection

Successful Eradication of Infection

Successful Fusion but Persistent Infection

Nichols et a192 Schoifet et a112° Bengston et al TM Figgie et al 1°3 Rand et a1114 Bliss et al TM Knutson et al 1°8 Broderson et a1115 Wasielewski Bose* et a139 Bose1- et a189 Ellingsen 1°2

7 39 21 22 25 16 15 40 10 9 7 10

7/7 (100%) 37/39 (95%) 20/21 (95%) 17/22 (77%) 23/25 (92%) 13/16 (81%) 15/15 (100%) 38/40 (95%) 10/10 (100%) 6/9 (66%) 7/7 (66%) 8/10 (100%)

0% 2 (5%) 1 (4%) 1 (4%) -3 (19%) -2 (5%) -2/9 failed fusion 2/7 failed fusion 2 (20%)

*One stage. tTwo stage.

needed to thoroughly debride the knee. I use standard tibial and femoral knee jigs to fine-tune the tibial and femoral cuts (to ensure accurate and adequate bone apposition). Vascular femoral bone must be fashioned to interdigirate with viable tibial bone over a maximal surface area to promote union. Good apposition will also improve the rigidity of the construct, paramount to infection eradication and bone healing. 92,~14Therefore, during initial debridement and prosthetic resection all possible bone that is viable and not infiltrated with cement should be preserved. Plating is best accomplished with a large fragment 4.5 plate medially and a large reconstruction plate anteriorly. The anterior plate is easily located along the femur, but the optimal position for tibial fixation can vary. It can be twisted to sit on the lateral aspect of the tibia, obtaining

coverage by the musculature in this region. It can also be positioned just medial to the tibial tubercle, although coverage is more difficult in this location. If coverage of the tibial portion of the plate becomes an issue, some or all of the tibial tubercle can be removed. Also, a lateral fasciocutaneous flap can be fabricated from the remaining redundant tissues. At arthrodesis bone grafting should be considered to improve the fusion rate in cases with deficient bone contact, n4 The rate of successful fusion is increased in knees that have minimally or partially constrained prosthesis and less associated bone loss. ~°7,]]5 On the other hand, hinged devices and devices with bulky stems have increased bone loss after removal, decreasing the potential for successful arthrodesis by diminishing potential contact area. 116 Excessive metaphyseal bone loss, after removal of an infected constrained or hinged prosthesis, also increases the technical difficulty of accomplishing good bony apposition at arthrodesis, ns,117The use of pulsing electromagnetic fields has also been suggested to improve the time to healing and success rates with fusions after infected TKA. 118 The common practice in primary arthrodesis is to fuse the knee in slight valgus and flexion to obtain a more physiological gait. 119The optimal position after removal of the infected knee prosthesis is closer to full extension to minimize the effect of bone loss on extremity shortening. In knees that are not reimplantable a successful arthrodesis is believed to give the most predictable long-term results. Even though this is considered to represent an end point of treatment, persistent local infections after successful arthrodesis have been reported. 1°1,1°3,12°These usually require long-term treatment with suppressive ATBs.

Fig 4. (A and B) Radiographs show a Imee fusion with a double-plating technique in an 80-year-old woman who presented with a 90 ° deformity after total knee replacement. She had been unable to bear weight on the extremity for the previous year and was unable to actively extend the leg because of a patella tendon rupture.

164

RAY C. WASIELEWSKI

AMPUTATION A m p u t a t i o n for the t r e a t m e n t of infection a r o u n d a TKA is rarely required. 4°,114 In a r e v i e w of the literature, R a n d 113 f o u n d that in 893 infected knees there w a s a 6% incidence of a m p u t a t i o n . M a n y of the patients requiring this salvage p r o c e d u r e h a v e h a d multiple failed a t t e m p t s at revision arthroplasty. 121 A m p u t a t i o n m a y also be c o m m o n after a failed infected hinge prosthesis w i t h severe b o n e loss. 98 Indications also include the following: life threatening persistent sepsis; a dysfunctional, unreconstructable joint; a dysvascular, g a n g r e n o u s limb; or intractable p a i n a n d instability. 122 These considerations m a y be particularly relevant in the severely debilitated Class C patient o r n u r s i n g - h o m e patient w i t h limited life expectancy.

TREATMENT AFTER FAILED TREATMENT Arthrodesis, pseudoarthrosis, and a m p u t a t i o n are often u s e d as salvage p r o c e d u r e s after failed a t t e m p t s at treating the infected TKA. Repeat two-stage r e i m p l a n t a t i o n h a s b e e n s h o w n to p r o d u c e g o o d results w i t h nine of the nine knees free of infection after a m e a n follow-up of 31 months. Arthrodesis has b e e n the m o s t u s e d m e t h o d for the t r e a t m e n t of the refractory infected TKA. Reports h a v e s h o w n v e r y high success rates in m a n y different studies. 95,11°I n t r a m e d u l l a r y arthrodesis m a y also be valuable in obtaining a successful o u t c o m e in patients w i t h reinfection after failed reimplantation. 9s W h e n all else fails, a m p u t a tion is the a p p r o p r i a t e m o d a l i t y in patients w h o h a v e h a d multiple failed revision attempts, particularly those w i t h severe b o n e loss a n d intractable pain.

SUMMARY W h e n an infection a r o u n d a TKA is diagnosed, it is i m p o r t a n t to chose an initial t r e a t m e n t m o d a l i t y b a s e d on w h e t h e r the infection is acute or chronic. If the acutely infected knee has no evidence of loosening a n d the organi s m is of low virulence a n d is susceptible to ATB, the patient should h a v e an a t t e m p t e d salvage of the prosthesis. Salvage is m o s t likely to succeed if the joint is aggressively a n d ( w h e n necessary) repetitively debrided. The a p p r o p r i ate parenteral ATBs should be g i v e n for 6 w e e k s b a s e d on sensitivity data. A n infectious disease specialist can help w i t h ATB selection a n d administration. The patient m u s t be m a d e to u n d e r s t a n d the risk of failure w i t h this m o d a l i t y despite these selective criteria. Chronic infections are m o s t successfully treated b y v i g o r o u s irrigation a n d d e b r i d e m e n t w i t h prosthetic resection, IV ATBs, a n d reimplantation. Eradication of the infection should be verified (prereimplantation) b y aspiration. Serial d e b r i d e m e n t should be p e r f o r m e d until intraoperative cultures a n d frozen sections are negative. ATBi m p r e g n a t e d spacers, in conjunction w i t h IV ATBs, m a y p r o v i d e additional bacteriocidal effects b y delivering local concentrations of ATBs that exceed o r g a n i s m m i n i m u m inhibitory concentrations b y several fold. Arthrodesis and p s e u d o a r t h r o s i s can be u s e d as reliable initial p r o c e d u r e s or as salvage p r o c e d u r e s for the t r e a t m e n t of the refractory infected TKA. THE INFECTED TOTAL KNEE ARTHROPLASTY

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