Preoperative Diagnosis of Periprosthetic Joint Infection: Role of Aspiration

Transcription

1 Musculoskeletal Imaging Clinical Perspective Musculoskeletal Imaging Clinical Perspective Matthew W. Squire 1 Craig J. Della Valle 2 Javad Parvizi 3 Squire MW, Della Valle CJ, Parvizi J Keywords: arthroplasty, hip, knee, periprosthetic joint infection, revision DOI: /AJR Received June 11, 2010; accepted after revision August 17, Department of Orthopedic Surgery, University of Wisconsin Hospitals and Clinics, 600 Highland Ave, Madison, WI Address correspondence to M. W. Squire (squire@ortho.wisc.edu). 2 Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL. 3 Department of Orthopaedic Surgery, Rothman Institute at Jefferson, Philadelphia, PA. AJR 2011; 196: X/11/ American Roentgen Ray Society Preoperative Diagnosis of Periprosthetic Joint Infection: Role of Aspiration OBJECTIVE. The purpose of this article is to illustrate how total knee arthroplasty (TKA) and total hip arthroplasty (THA) aspiration by the radiologist can assist the health care team in determining the presence or absence of periprosthetic joint infection. CONCLUSION. The increasing incidence of periprosthetic TKA and THA infection, as well as the changing role of aspiration for diagnosing periprosthetic joint infection, will likely increase demand for this important procedure in the future. I n the United States, deep periprosthetic joint infection is currently the most common indication for revision total knee arthroplasty (TKA) [1] and the third most frequent indication for revision total hip arthroplasty (THA) [2]. Overall, the incidence of periprosthetic joint infection and subsequent TKA or revision THA failure is estimated to be between 1% and 3% [3]. Periprosthetic joint infection inflicts significant physical and psychologic morbidity on patients and places immense financial burdens on both patients and society. Sequelae of periprosthetic joint infection can result in decreased knee or hip function; diminished patient quality of life; and in some cases arthrodesis, amputation, or permanent resection arthroplasty [4]. The management of aseptic TKA and THA failure fundamentally differs from that of periprosthetic joint infection [4]. Revision TKA and THA procedures for aseptic failure focus on restoration of hip and knee function and can be performed in most cases as a single surgical intervention. In contrast, treatment of periprosthetic joint infection revolves around eradication of infection followed by subsequent restoration of hip or knee function; therefore, chronic periprosthetic joint infection is optimally treated with a twostage surgical approach [4]. Implant removal, joint débridement, antibiotic-loaded cement spacer placement, and parenteral antibiotic therapy are performed as the first stage to eradicate infection followed by the second stage in which revision components are im- planted to restore TKA or THA function [4]. Failure to recognize periprosthetic joint infection as the cause of TKA or THA failure subjects patients to revision procedures with unacceptably low probability of success because the cause of TKA or THA demise has not been addressed. Therefore, preoperative testing modalities that provide accurate and timely information regarding the sterility of hip and knee implants are of paramount importance to the health care team. Because the clinical presentation of periprosthetic joint infection can be subtle and other modes of TKA and revision THA failure can coexist with periprosthetic joint infection [4], the diagnosis of TKA and THA sepsis can be challenging for both musculoskeletal and nonmusculoskeletal care providers. Despite a thorough patient history, physical examination, multiple diagnostic tests, and complex algorithms, differentiating periprosthetic joint infection from aseptic loosening of TKA and THA can be difficult in some cases [5]. The purpose of this article is to illustrate how TKA and THA aspiration by the radiologist can assist the health care team in determining the presence or absence of periprosthetic joint infection. Periprosthetic Joint Infection Diagnostic Criteria At this time, there is no single reference standard diagnostic test for identification of periprosthetic joint infection. Literature review reveals that the incidence of false-positive culture results from preoperative hip aspiration ranges from 3% to 16% [6 9]. Recent evidence shows AJR:196, April

2 the incidence of false-positive and false-negative culture results from TKA or THA tissue biopsy is as high as 6% and 10%, respectively [3]. Because of this, many authors no longer consider cultures obtained from preoperative joint aspiration or tissue biopsy to be the reference standard test for diagnosis of TKA or THA infection [10 13]. Currently, the diagnosis of periprosthetic joint infection relies on a combination of clinical judgment, preoperative serologic testing, information obtained from TKA or THA aspiration, and microbiologic as well as histopathologic testing of tissue or fluid obtained at the time of surgery [3]. At this time, the optimal combination of diagnostic and intraoperative tests to confirm or exclude the presence of periprosthetic joint infection has not been defined. History and Physical Examination A thorough evaluation of medical and surgical history as well as physical examination is an excellent screening tool for periprosthetic joint infection and helps guide subsequent diagnostic evaluation. Several comorbidities have been associated with periprosthetic joint infection: diabetes mellitus, obesity, inflammatory arthritis including rheumatoid arthritis, chronic renal failure, malnutrition, use of corticosteroids, skin disorders such as psoriasis, and immunocompromised state. Identification of these risk factors should raise the possibility of periprosthetic joint infection as the cause of pain or failure. Rapid unexplained TKA or THA failure [14], wound healing problems [15, 16], extended perioperative antibiotic administration [16], or repeat surgery are historical findings often associated with periprosthetic joint infection [3]. Purulent TKA and THA infection is relatively rare and periprosthetic joint infection often occurs without overt local or systemic manifestations. However, subtle physical examination findings, such as wound erythema, knee effusion, or other fluid collections, may be present in acute or chronic periprosthetic joint infection. The presence of an active or healed sinus tract communicating with the joint space is diagnostic for periprosthetic joint infection [16]. Imaging Evaluation Radiographs are widely used in the initial evaluation of painful TKA and THA and can detect periprosthetic fractures, changes in implant position, osteolysis, and findings consistent with periprosthetic joint infection. To better define the ability of radiographs to diagnose THA sepsis, Tigges et al. [17] retrospectively reviewed radiographs of a known cohort of infected THA procedures and found that 50% of radiographs in this cohort were normal. Twenty percent of radiographs in this study showed abnormalities that are commonly associated with aseptic loosening and 10% of radiographs showed nonspecific findings [17]. Findings more commonly associated with infection, such as periosteal reaction and rapidly developing periprosthetic radiolucencies, were identified in 20% of radiographs [17]. Although radiographs lack appropriate sensitivity and specificity to diagnose or exclude periprosthetic joint infection, they are useful in the initial evaluation of painful and potentially infected THA or TKA because they can detect radiographic changes highly suggestive of periprosthetic joint infection that can guide further diagnostic testing [17]. Because of technical imaging improvements that reduce metallic image artifact due to beam hardening and magnetic susceptibility, CT and MRI are being increasingly used as preoperative planning tools for revision procedures and the evaluation of painful hip and knee replacements [18]. However, their role in the diagnosis of periprosthetic joint infection is not clear. The absence of joint effusion with TKA or THA appears to have a negative predictive value of 96% for periprosthetic joint infection [18]. Periostitis seen on CT in association with TKA and THA is extremely sensitive (100%) for periprosthetic joint infection but poorly specific (16%). Concomitant joint distention and soft-tissue fluid collections around a THA or TKA increase specificity of periostitis as a marker for periprosthetic joint infection to 87% [18]. MRI is able to detect intraarticular pathology such as synovitis after THA [19]; however, at this time, MRI signal characteristics and findings that can distinguish aseptic loosening from periprosthetic joint infection are not known [18]. Currently, CT and MRI are not considered to be first-line imaging modalities for evaluating TKA and THA for potential periprosthetic joint infection. The role of radionuclide imaging and 18 F- FDG PET in assessing patients for periprosthetic joint infection has expanded. In a study of 72 TKA and THA patients examined with bone marrow scintigraphy, Levitsky et al. [20] reported sensitivity of 33%, specificity of 86%, positive predictive value (PPV) of 30%, and negative predictive value (NPV) of 88% [20] when using this imaging modality to confirm or exclude the presence of periprosthetic joint infection. In vitro WBC labeling with 111 In combined with 99m Tc sulfur colloid marrow imaging has been reported to provide very high sensitivity (96%), specificity (97%), and accuracy (97%) and is regarded as the preferred radionuclide test for confirming or excluding periprosthetic joint infection as the cause of implant failure [21]. FDG PET has also shown reasonable utility for diagnosis or exclusion of TKA and THA infections. When evaluating painful TKA and THA for infection, Chryssikos et al. [22] showed FDG PET yielded 95% sensitivity, 93% specificity, 80% PPV, and 98.5% NPV. On the basis of these investigations, advanced radiographic imaging appears to have a role in determining the presence or absence of periprosthetic joint infection; however, availability, timeliness, and cost of these advanced imaging modalities have limited their widespread use. Serologic Tests It has been shown that serologic studies of systemic inflammation, specifically C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), have excellent sensitivity (91% and 93%, respectively) when used as diagnostic tests to exclude the presence of periprosthetic joint infection [23]. Because of their high sensitivity, minimal patient morbidity, and widespread availability, these tests have become first-line screening tests when evaluating patients for periprosthetic joint infection. In a level 1 study of 207 consecutive TKA revisions, if both ESR and CRP were normal, the probability of periprosthetic joint infection was 3% [23]. In contrast, the ability of these tests to confirm the presence of periprosthetic joint infection was less optimal. When both ESR and CRP were elevated, the PPV for periprosthetic joint infection was 84% [23]. It was acknowledged by the authors that recent surgery and certain medical disorders may elevate the ESR and CRP, which might diminish the reliability of these tests to identify periprosthetic joint infection. The authors concluded that when both ESR and CRP are normal, a low likelihood of periprosthetic joint infection exists, but when either ESR or CRP is elevated, further testing for periprosthetic joint infection is indicated. Aspiration The role of aspiration in the evaluation and management of failed TKA and THA replacements has evolved over the past two decades. A paradigm shift regarding the optimal patient population to aspirate [24, 25], fluid assays to 876 AJR:196, April 2011

3 perform at the time of aspiration [26, 27], and role of aspiration in determining the presence or absence of periprosthetic joint infection has occurred as a result of evidence-based medicine [3, 28, 29]. Recent level I and II investigations have shown that aspiration and subsequent synovial fluid analyses play a pivotal role in the management of failed hip and knee replacements [3, 28, 29]. Traditionally, TKA and THA aspirations were performed to obtain fluid for bacterial culture, which then determined the presence or absence of periprosthetic joint infection. Culture required multiple days before periprosthetic joint infection could be confirmed or excluded, which frequently delayed patient care. Investigations seeking to define the utility of cultured synovial fluid in confirming or excluding periprosthetic joint infection have shown a wide range of sensitivity (50 93%) and specificity (82 97%) [30] as well as a modest to high incidence of false-positive culture results (3 16%) [6 9]. Multiple investigations illustrate how periprosthetic joint infection incidence affects the predictive value of aspiration and synovial fluid culture (Bayes theorem). In a patient population with 2% incidence of periprosthetic joint infection, THA aspiration and synovial fluid culture in all patients undergoing revision THA yielded 60% sensitivity, 88% specificity, 13% false-positive incidence, 15% PPV, 98% NPV, and 87% accuracy [24]. A similar study in a revision TKA cohort with 29% periprosthetic joint infection revealed 55% sensitivity, 96% specificity, 85% PPV, 84% NPV, and 84% accuracy [25]. Ali et al. [30] in a recent level 1 study showed that selective THA aspiration in a cohort of patients with 23% periprosthetic joint infection incidence produced 82% sensitivity, 91% specificity, 74% PPV, 94% NPV, and 89% accuracy. In this study, patients with one or more of the following characteristics underwent revision THA aspiration: clinical or radiographic suspicion for infection, elevated ESR or CRP, presence of any disorder that may elevate ESR or CRP coupled with clinical suspicion for infection, history of wound infection or problems, and implant failure less than 5 years from the date of primary THA [30]. The time required to complete synovial fluid culture combined with its modest accuracy even in highly selected patient populations has prompted investigators to develop and define more rapid and reliable synovial fluid analyses for diagnosing periprosthetic joint infection. More recently, the use of the synovial fluid WBC count with analysis of polymorphonuclear (PMN) percentage has gained popularity as an outstanding test for differentiating periprosthetic joint infection from aseptic TKA and THA failure [28]. TKA and THA synovial fluid WBC count and PMN percentage are inexpensive and rapid tests that can be performed before surgery in most institutions. The synovial fluid WBC count and PMN percentage can be used in isolation or conjunction with serologic tests to accurately determine the probability of joint infection [28]. One recent level II study indicated synovial WBC count combined with synovial fluid PMN percentage was more accurate than aspiration and culture for diagnosing periprosthetic joint infection [3]. Septic arthritis of a native joint has historically been associated with synovial fluid containing greater than 50,000 WBC/µL, of which greater than 75% are PMNs [31]. In general, synovial fluid WBC counts of infected TKA and THA are much lower than that of infected native joints [26 29]. A recent level II study of revision TKA showed via the receiver operating characteristic that synovial fluid WBC counts lower than 1100 WBC/µL containing less than 64% PMNs resulted in 99.6% NPV for excluding periprosthetic joint infection [3]. Another recent level I study used the receiver operating characteristic to show that a synovial fluid WBC count greater than 9000 WBC/ µl combined with elevation of either the ESR or CRP resulted in a 100% PPV and 98% accuracy for identifying periprosthetic joint infection [28]. Both of these studies indicated the utility of synovial PMN percentage for detecting periprosthetic joint infection was greatest when used in combination with synovial fluid WBC count, and PMN percentages greater than 65% should raise suspicion for periprosthetic joint infection [3, 28, 29]. Level I studies by Schinsky et al. [28] and Della Valle et al. [29] have indicated that if ESR and CRP are both elevated, periprosthetic joint infection is likely present if TKA or THA synovial fluid WBC counts are greater than 3000 WBC/µl. Synovial fluid WBC count can be especially useful for identifying or excluding periprosthetic joint infection in time-sensitive clinical scenarios. In cases of well-functioning hip or knee replacements that become acutely painful or systemic sepsis with unclear cause, the possibility of TKA or THA infection often needs to be excluded in an accurate and expedient manner. In clinical situations such as these, aspiration and synovial fluid WBC count with or without complimentary PMN percentage is the fastest and most accurate means by which to confirm or exclude periprosthetic joint infection of the TKA or THA in question. Technical Considerations Aspirations of hip and knee joints present different challenges to the health care team. Most musculoskeletal providers are hesitant to attempt aspiration of the hip joint without fluoroscopic guidance because of its distance from the skin, adjacent anatomic neurovascular structures, and poor probability of blindly entering the joint space. Because of its subcutaneous location, musculoskeletal providers are often able to aspirate the knee joint and recover fluid for culture and cell count analyses. However, in some instances (e.g., morbid obesity, postsurgical scar tissue, superficial tissue cellulitis covering the joint line, etc.), aspiration of the knee joint may be challenging for even seasoned musculoskeletal providers. Therefore, radiographic guidance and technical expertise of a radiologist is often necessary to obtain joint fluid from prosthetic TKA or THA joints. Ideally, fluid obtained at the time of TKA or THA aspiration should be sent for a synovial fluid WBC count, differential, and aerobic culture. In general, if the volume of fluid recovered will not allow multiple analyses, cell count and differential should be prioritized over culture. However, communication between the radiologist and orthopedist is essential to ensure fluid assay prioritization is appropriate for each individual clinical scenario. Currently, it is unclear if anaerobic, fungal, or acid-fast bacilli cultures should be routinely sent because of their cost; however, in patients with strongly suspected periprosthetic joint infection and negative initial aerobic cultures, these tests should be performed if repeat aspiration is planned. Despite the excellent ability of synovial WBC count and differential to identify periprosthetic joint infection, synovial fluid cultures should be simultaneously sent with WBC count and differential if volume of the aspirate allows. The information obtained from these different assays is complimentary [3, 28, 29]. Positive synovial fluid cultures further confirm the presence of periprosthetic joint infection and allow speciation and resistance testing of the infecting organisms. If two-stage revision surgery is planned, knowledge of periprosthetic joint infection organisms and antimicrobial AJR:196, April

4 resistance patterns before surgery allows the orthopedic surgeon and infectious disease teams to optimize antibiotic agents included in temporary spacers and perioperative antibiotic therapy [4]. At the time of aspiration, a dry tap in which fluid is not recoverable from the TKA or THA may be encountered despite appropriate anatomic location within the prosthetic hip or knee joint capsule. Absence of recoverable fluid within the joint does not imply that periprosthetic joint infection is not present [30]. In a study investigating the utility of hip aspiration, a dry tap was present in 23% of THAs and the volume of fluid recovered from infected and sterile THAs was nearly identical [30]. In this investigation, dry joints were washed with nonbacteriostatic saline and culture of recoverable saline was performed. This technique yielded 83% sensitivity, 93% specificity, 63% PPV, 93% NPV, and 83% accuracy when compared with tissue culture obtained at the time of revision surgery [30]. If saline wash of the joint cavity is performed due to the absence of recoverable synovial fluid, WBC count and PMN percentage of recovered fluid do not provide useful information [30]. Saline wash may be useful in situations in which it is imperative to identify an organism to optimize patient treatment. However, many orthopedic surgeons are hesitant to order this procedure, fearing contamination of a previously sterile joint arthroplasty, and would prefer to attempt recovery of organisms via intraoperative tissue biopsy. Therefore, contacting the health care team ordering the aspirate before saline wash of a dry tap joint is advised. It is our practice preference to confirm or exclude periprosthetic joint infection via indium-sulfur-colloid or FDG PET and recover organisms via tissue biopsy at the time of surgery in most clinical scenarios. The effect of systemic antibiotics as well as bacteriostatic saline and local anesthetics on TKA and THA synovial fluid cultures has previously been determined. It is critical that systemic antibiotics not be administered to the patient suspected of periprosthetic joint infection until a deep culture has been obtained and the diagnosis confirmed; only hemodynamic instability secondary to frank sepsis should supersede this axiom. Unfortunately, in clinical practice many patients are started on antibiotics before a definite diagnosis is made. Although the effect of systemic antibiotics on the synovial fluid WBC count and differential is unknown, the effect of systemic antibiotics and bacteriostatic saline or local anesthetics on cultures has been studied and shown to markedly decrease the probability of organism recovery at the time of aspiration [25]. This work has shown that patients should be off of antibiotics for a minimum of 2 weeks before a culture is obtained to avoid a false-negative culture; although in practice we typically avoid a hip aspiration within a month of antibiotic administration, given the increased pain and risks associated with hip as opposed to knee aspiration. Additionally, it has been shown that the introduction of bacteriostatic compounds, such as saline or local anesthetic, into the joint cavity at the time of aspiration increases the probability of false-negative culture results [25]. In the patient in whom a negative culture has been obtained but there is a high suspicion for infection, repeat aspiration should be obtained and cultures sent not only for aerobic but also for anaerobic, fungal, and acid-fast bacilli cultures, which can occasionally be pathogens that cause periprosthetic joint infection. Because Staphylococcus epidermidis is among the most common organisms that cause periprosthetic joint infection, great care with sterile technique must be exercised when performing aspiration of a prosthetic joint to prevent false-positive results. The introduction of bacteria within the replaced joint can also occur with the potential disastrous consequence of causing periprosthetic joint infection. As previously discussed, aspiration of the knee joint can usually be performed in the office without radiographic imaging and is most easily accomplished using a standard length, 18- or 20-gauge needle with or without a stylet; the use of smaller gauge needles may lead to far greater difficulty in aspiration. If a hip aspiration is to be performed, spinal needles are typically required, and it is recommended that the clinician keep the stylet in place until the joint has been entered to prevent soft tissue from blocking the tip of the needle. As with knee aspiration, the use of smaller gauge needles is discouraged because they may not have adequate strength to penetrate the soft tissues around the hip joint without bending and they increase the difficulty of withdrawing synovial fluid, particularly if the fluid is viscous (as may be present in periprosthetic joint infection) leading to the inability to obtain an adequate sample and the use of a 20-gauge needle is common in our practices. Summary In the United States, the incidence of periprosthetic joint infection is growing disproportionally faster than the increasing numbers of TKA and THA being performed each year [1, 2]. Failure to recognize this problem results in unnecessary patient morbidity and disability as well as surgical interventions that have unacceptably low probability of success. Management of periprosthetic joint infection often requires two-stage revision procedures, which fundamentally differ from that of aseptic TKA and THA failure [4]. Currently, the diagnosis of periprosthetic joint infection relies on a combination of clinical judgment and diagnostic testing [3]. As with most medical and surgical problems, the evaluation for periprosthetic joint infection begins with a thorough medical history, physical examination, and appropriate radiographic imaging [3]. Serologic markers of systemic inflammation, ESR and CRP, are extremely useful for ruling out periprosthetic joint infection and should be used as first-line screening tests for periprosthetic joint infection [23]. As a result of evidence-based medicine, the patient selection for TKA and THA aspiration, fluid analyses performed at the time of aspiration and the importance of aspiration in determining the probability of periprosthetic joint infection have evolved significantly over the past 20 years [3, 28 30]. Level I and II studies of TKA and THA aspiration with synovial fluid WBC count, differential, and culture indicate it is the cornerstone of the diagnostic algorithm for confirmation or exclusion of periprosthetic joint infection [3, 28, 29]. The increasing incidence of periprosthetic joint infection, the role of aspiration for diagnosing periprosthetic joint infection, and the technical skills necessary to perform TKA and THA aspiration will likely increase demand for this important procedure in the future. References 1. Kurtz SM, Ong KL, Lau E, Bozic KJ, Berry D, Parvizi J. Prosthetic joint infection risk after TKA in the Medicare population. Clin Orthop Relat Res 2010; 468: Ong KL, Kurtz SM, Lau E, Bozic KJ, Berry DJ, Parvizi J. Prosthetic joint infection risk after total hip arthroplasty in the Medicare population. J Arthroplasty 2009; 24: Parvizi J, Ghanem E, Sharkey P, Aggarwal A, Burnett RSJ, Barrack RL. Diagnosis of infected total knee: findings of a multicenter database. 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