Diagnosing the Infected Total Knee Arthroplasty


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Diagnosing the Infected Total Knee Arthroplasty


Mina Tohidi MD and John F. Rudan MD


Division of Orthopaedic Surgery, Department of Surgery, Queen’s University, Kingston, ON, Canada


Clinical scenario



  • A 54‐year‐old male presents to clinic six months after right primary TKA. He reports a three‐week history of progressive right knee erythema. He started using crutches in the last week due to worsening pain with activity.
  • He was assessed in the Emergency Department earlier that week and prescribed oral cephalexin for suspected cellulitis of the right extremity. Bloodwork from that visit shows elevated erythrocyte sedimentation rate (ESR), elevated C‐reactive protein (CRP), and normal serum white blood cell (WBC) count. An aspirate was not done.
  • The patient denies any recent travel, illness, or dental visits.

Top three questions



  1. In patients with signs and symptoms of infection, what is the sensitivity and specificity of synovial fluid cytology, compared to preoperative serologic investigations, for diagnosis of TKA infection?
  2. In patients with signs and symptoms of TKA infection, what intraoperative measures can be used for identification of joint infection?
  3. For patients with failed two‐stage prosthetic exchange secondary to infection, how do patient outcomes compare for repeat attempts at implant exchange, compared to arthrodesis or amputation?

Question 1: In patients with signs and symptoms of infection, what is the sensitivity and specificity of synovial fluid cytology, compared to preoperative serologic investigations, for diagnosis of TKA infection?


Rationale


Identification of the microbial pathogen(s) is critical to the diagnosis of TKA infection. However, traditional aspiration and tissue cultures may not be sufficient to identify a pathogen for two main reasons: (i) it may be difficult to culture biofilm‐associated organisms in the laboratory and (ii) the preoperative and postoperative use of antibiotics can make culture results negative.1 For patients with this type of presentation, alternative, nonmicrobiological testing methods are critical for diagnosis of TKA infection.


Clinical comment


Identification of the microbial pathogen(s) is essential for diagnosis of TKA infection and for selection of appropriate pathogen‐specific antimicrobial therapy. There has been growing interest in using nonculture‐based methods to diagnose TKA infection.


Available literature and quality of the evidence


Level I and II evidence exists to answer this question.


Findings


The initial history and physical exam are crucial to the diagnosis of periprosthetic joint infection (PJI). Patient risk factors and perioperative risk factors should be identified.2 Blood tests, including serum ESR and CRP have high sensitivity, good negative predictive value, and are cost‐effective screening tools.3 ESR sensitivity and specificity are 75% (95% confidence interval [CI]: 72–77%) and 70% (95% CI: 68–72%), respectively.4 CRP sensitivity and specificity are 88% (95% CI: 86–90%) and 74% (95% CI: 71–76%), respectively.4 These blood tests can be used as adjuncts to synovial fluid cytology with WBC differential and synovial fluid culture, which have sensitivities of 90% (95% CI: 78–96%) and 62% (95% CI: 50–74%) and specificities of 91% (95% CI: 80–96%) and 94% (95% CI: 91–96%), respectively, for diagnosis of TKA infection.5,6 Since inflammatory markers such as ESR and CRP may remain elevated for up to several months following primary TKA, they may be less useful for identifying early postoperative infection.7 Thresholds for chronic PJI have been identified.8


With sensitivity and specificity of 45% (95% CI: 41–49%) and 87% (95% CI: 85–89%), respectively, serum WBC count is not as useful as serum ESR or CRP for diagnosis of TKA infection.2,4 Serum interleukin 6 (IL‐6) may be a more specific marker of acute infection, but it is not be available in all laboratories.2 Estimated sensitivity and specificity for IL‐6 are 97% (95% CI: 93–99%) and 91% (95% CI: 87–94%), respectively.4 Overall, the diagnostic accuracy for PJI is best for IL‐6, followed by CRP, ESR, and WBC count.4


A novel approach to PJI diagnosis involves synovial fluid inflammatory biomarkers, such as alpha‐defensin. The alpha‐defensin assay offers another test with excellent sensitivity and specificity (100% CI: 79–100% and 95% CI: 83–99%, respectively) for diagnosis of PJI, and it is now available for clinical use.2,9,10 Though preliminary data suggest that alpha‐defensin 1 is at least equivalent to other diagnostic modalities, larger studies are required to confirm this finding.10


Clinical resolution



  • ESR and CRP have excellent diagnostic test performance for chronic TKA infection and should be used as initial screening tools and adjuncts to synovial fluid cytology and culture (level I).
  • The diagnostic accuracy of preoperative serologic investigations for PJI is best for IL‐6, followed by CRP, ESR, and WBC count (level II).
  • Emerging investigations, such as serum IL‐6 and synovial alpha‐defensin testing, demonstrate improved sensitivity and specificity for detecting TKA infection (level II).

Question 2: In patients with signs and symptoms of TKA infection, what intraoperative measures can be used for identification of joint infection?


Rationale


Infection is the leading indication for revision surgery after TKA, and yet there is no gold standard for diagnosis. For patients with an indeterminate presentation, adjunct intraoperative investigations are required to confirm diagnosis of TKA infection.


Clinical comment


On some occasions, patients have poor function of their TKA without any abnormal preoperative investigations. In these situations, surgeons are faced with important challenges: (i) do we take the patient to the operating room despite clear documentation of infection and (ii) are there any intraoperative investigations that can help identify TKA infection?


Available literature and quality of the evidence


Level I evidence is available to answer this question.


Findings


The use of polymerase chain reaction (PCR) technologies to diagnose PJIs by detecting bacterial deoxyribonucleic acid (DNA) has received much attention in recent years. The theoretical advantages of PCR compared to intraoperative tissue cultures include higher sensitivity, faster turnaround time, and lack of dependence on prior antibiotic treatment.11 Tissue, synovial fluid, and sonicated prostheses fluid samples can be used for PCR analysis.11 Tissue samples have the highest sensitivity at 95% (95% CI: 91–99%), while sonicated prosthesis fluids have this highest specificity at 96% (95% CI: 92–100%).11

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Nov 28, 2021 | Posted by in ORTHOPEDIC | Comments Off on Diagnosing the Infected Total Knee Arthroplasty
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