Key points

Introduction

Total hip arthroplasty (THA) is one of the most successful operations in the history of orthopedic surgery. Modeled on the low-friction arthroplasty introduced by Sir John Charnley in 1961, the modern THA has relieved pain and improved quality of life for millions of individuals worldwide.

Total knee arthroplasty (TKA) gained popularity shortly after the advent of the modern THA, and, in 1972, Insall introduced the total condylar prosthesis, which laid the framework for the modern TKA. Despite these developments, knee replacements were less successful than their hip counterparts because of complications with prosthetic design, and it was not until the 1990s that the total knee replacement was considered a successful operation.

Presently, THA and TKA are among the most effective and widely performed surgical operations, with close to 1 million THAs and TKAs performed in the United States annually. The number of joint replacements performed each year is also growing rapidly, with a 174% and 673% increase in annual procedures projected by 2030 for THA and TKA, respectively. Given the considerable growth and success of total joint replacements over the past several decades, there has been a major focus on minimizing surgical complications in order to further improve long-term outcomes and drive down costs.

Periprosthetic joint infection (PJI) remains a major cause of failure in THA and TKA, despite an incidence of less than 2% in most national centers. For both THA and TKA, PJI is the third leading cause of primary failure, the leading cause of revision failure, and the leading cause of early primary failure (<5 years), which is a pertinent issue because PJI-associated revision results in a mortality 5 times greater than in revision following aseptic failure. Furthermore, the financial burden of PJI is significantly greater than in uninfected cases, with a 76% and 52% increase in cost for infected THA and TKA, respectively. With the significant added strain on patient outcomes and health care costs, the accurate and timely diagnosis of PJI is critical to the progressive improvement of modern arthroplasty.

Introduction

Total hip arthroplasty (THA) is one of the most successful operations in the history of orthopedic surgery. Modeled on the low-friction arthroplasty introduced by Sir John Charnley in 1961, the modern THA has relieved pain and improved quality of life for millions of individuals worldwide.

Total knee arthroplasty (TKA) gained popularity shortly after the advent of the modern THA, and, in 1972, Insall introduced the total condylar prosthesis, which laid the framework for the modern TKA. Despite these developments, knee replacements were less successful than their hip counterparts because of complications with prosthetic design, and it was not until the 1990s that the total knee replacement was considered a successful operation.

Presently, THA and TKA are among the most effective and widely performed surgical operations, with close to 1 million THAs and TKAs performed in the United States annually. The number of joint replacements performed each year is also growing rapidly, with a 174% and 673% increase in annual procedures projected by 2030 for THA and TKA, respectively. Given the considerable growth and success of total joint replacements over the past several decades, there has been a major focus on minimizing surgical complications in order to further improve long-term outcomes and drive down costs.

Periprosthetic joint infection (PJI) remains a major cause of failure in THA and TKA, despite an incidence of less than 2% in most national centers. For both THA and TKA, PJI is the third leading cause of primary failure, the leading cause of revision failure, and the leading cause of early primary failure (<5 years), which is a pertinent issue because PJI-associated revision results in a mortality 5 times greater than in revision following aseptic failure. Furthermore, the financial burden of PJI is significantly greater than in uninfected cases, with a 76% and 52% increase in cost for infected THA and TKA, respectively. With the significant added strain on patient outcomes and health care costs, the accurate and timely diagnosis of PJI is critical to the progressive improvement of modern arthroplasty.

Diagnostic criteria for periprosthetic joint infection

The diagnostic requirements for PJI have been a source of uncertainty in the past, with conflicting criteria resulting in the inability to form a universal clinical definition. In 2011, the Musculoskeletal Infection Society proposed a unique set of PJI criteria that, following further revision, was accepted by the US Centers for Disease Control and Prevention. Of note, because of discrepancies in the magnitude of clinically meaningful biomarker increases in acute (<6 weeks) versus chronic (>6 weeks) PJI, the International Consensus Meeting (ICM) on PJI suggested specific biomarker threshold values that are reflected in the minor criteria of PJI in the definition given later.

Definition of periprosthetic joint infection

Joint or bursa infections must meet at least 1 of the following criteria:

• 1.
  

  Two positive periprosthetic (tissue or fluid) cultures with matching organisms.

  
  
• 2.
  

  A sinus tract communicating with the joint ( Fig. 1 ).

  
  

  
  

  
  

  

  
  

  
  

  Typical physical examination findings for PJI after TKA. Note the opening and drainage at the distal aspect of the incision.

  
  
  
  
• 3.
  

  Having 3 of the following minor criteria:

  
  
  
  
  • a.
    

    Increased serum C-reactive protein (CRP) level (>100 mg/L in acute PJI; >10 mg/L in chronic PJI) and erythrocyte sedimentation rate (ESR; not applicable to acute PJI; >30 mm/h in chronic PJI)

    
    
  • b.
    

    Increased synovial fluid white blood cell (WBC) count (>10,000 cells/μL in acute PJI; >3000 cells/μL in chronic PJI) or ++ (or greater) change on leukocyte esterase test strip of synovial fluid

    
    
  • c.
    

    Increased synovial fluid polymorphonuclear neutrophil percentage (PMN%) (>90% in acute PJI; PMN% >80% in chronic PJI)

    
    
  • d.
    

    Positive histologic analysis of periprosthetic tissue (>5 neutrophils [PMNs] per high-power field [HPF])

    
    
  • e.
    

    A single positive periprosthetic (tissue or fluid) culture

  
  

Even with the establishment of firm diagnostic criteria, the ICM noted that, if clinical suspicion for PJI is high, further diagnostic evaluation should commence even if the criteria listed earlier are not met in full. For this reason, risk stratification, based on patient history, physical examination, and joint radiographs, is critical to establishing a diagnosis in cases lacking a straightforward diagnosis.

Also of note, The Society of Unicondylar Research and Continuing Education suggested that these criteria, including ESR and CRP threshold values, can also be used in suspected PJI following unicompartmental knee arthroplasty (UKA), but that the aspiration biomarker thresholds in UKA can deviate significantly from the ICM values for TKA.

Diagnostic modalities in suspected periprosthetic joint infection

Before constructing a stepwise approach to diagnosing PJI, it is essential to understand the clinical utility of the various diagnostic modalities. The mainstays in the evaluation of PJI include:

• 1.
  

  Detailed history, physical examination, and risk factor identification

  
  
• 2.
  

  Joint radiographs

  
  
• 3.
  

  ESR and CRP serology

  
  
• 4.
  

  Joint aspiration and culture

Additional diagnostic tools are useful on a conditional basis and are discussed later.

An algorithmic approach to diagnosing periprosthetic joint infection

In order to apply the diagnostic modalities in an organized fashion while minimizing invasive interventions, the authors propose a modification of the American Academy of Orthopaedic Surgeons’ diagnostic algorithm that accounts for more recent clinical data and recommendations ( Fig. 2 ). In all cases, this algorithm should not be used as a definitive diagnostic tool, but as an adjunct to clinical expertise and planned care. Furthermore, a high clinical suspicion should supersede any negative PJI diagnosis acquired through use of the algorithm.

Diagnostic algorithm for PJI. −, negative; +, positive; AFB, acid-fast bacilli. ^a If no fluid is drained, repeat aspiration. If 2 consecutive dry taps occur, proceed to biopsy with micro and histology. A + biopsy indicates likely infection and a − biopsy indicates unlikely infection. ^b Repeat joint aspiration is strongly encouraged in cases of high clinical suspicion, even in the absence of increased synovial biomarkers on initial aspiration. ^c As determined by history, physical examination, and radiography.

Patient history, physical examination, and risk factor identification

As with any postoperative complication, a focused history and physical is the first step in raising sufficient clinical suspicion for further work-up. For PJI, the clinical presentation varies significantly according to time frame and pathogen ( Table 1 ).

Because of a lack of empirical evidence regarding risk stratification in suspected PJI, underlying risk factors are another useful tool in stratifying patients into high-risk and low-risk categories.

• 
  

  Predisposing risk factors for periprosthetic joint infection

  
  
• •
  

  Local risk factors

  
  
  
  
  • ○
    

    Superficial surgical site infection

    
    
  • ○
    

    Joint malignancy

    
    
  • ○
    

    History of native joint septic arthritis

    
    
  • ○
    

    History of prior PJI

    
    
  • ○
    

    Prior arthroplasty of joint

    
    
  • ○
    

    Skin ulcers

    
    
  • ○
    

    Postoperative hematoma formation

  
  
  
  
• •
  

  Systemic risk factors

  
  
  
  
  • ○
    

    National Nosocomial Infections Surveillance System surgical patient risk index score of 1 or 2

    
    
  • ○
    

    Systemic malignancy

    
    
  • ○
    

    Rheumatoid arthritis

    
    
  • ○
    

    Immunocompromised host

    
    
  • ○
    

    Diabetes mellitus

    
    
  • ○
    

    Increased body mass index

    
    
  • ○
    

    Intravenous drug use

    
    
  • ○
    

    Steroid therapy

    
    
  • ○
    

    Systemic skin conditions

    
    
  • ○
    

    Increased duration of surgery

  
  

Imaging studies

Owing to their ease of use, rapid turnover, low associated costs, and ability to rule out other causes of joint pain, plain radiographs are the imaging study of choice despite their low sensitivity and specificity in diagnosing PJI. It is presently unclear whether or not computed tomography and MRI have a place in the routine diagnostic evaluation of PJI, because prosthesis-borne artifacts preclude reliable image interpretation, and the current MRI artifact reduction software is largely incapable of adequately ameliorating this issue. The utility of ultrasonography is limited to PJI with significant local fluid accumulation, and for PET scans and other forms of nuclear imaging further studies are needed, because the present data regarding accuracy are conflicting. Leukocyte scans and bone scans are generally not recommended because of unavailability and invasiveness, respectively.

• 
  

  Common radiographic findings in periprosthetic joint infection

  
  
• •
  

  Focal osteolysis, as indicated by a widened (>2 mm) band of radiolucency at the metal-bone interface or cement-bone interface

  
  
• •
  

  Loosening of components, particularly in a rapid and aggressive fashion characteristic of infectious loosening (vs the slow progression of aseptic loosening)

  
  
• •
  

  Cement fractures

  
  
• •
  

  Subperiosteal reaction