This article is more than 5 years old. Information may no longer be current.
Is RNA-based polymerase chain reaction a promising molecular technique for diagnosis of periprosthetic joint infection?
Click Here to Manage Email Alerts
by Farbod Rastegar, MD; and Javad Parvizi MD, FRCS
Total joint arthroplasty is considered an important orthopedic advancement for improving the quality of life of patients suffering from disabling disease. With the increasing popularity of these procedures, as surgeons, it is important to accurately diagnose and manage the secondary complications that affect patient outcome.
Amongst the many causes of prosthetic failure, infection is considered to be the most catastrophic. Various diagnostic modalities have been developed to detect periprosthetic joint infection (PJI). However, there are fundamental limitations associated with each technique. The use of polymerase chain reaction (PCR) to detect the presence of infection, as well as enable organism profiling, has the capacity to revolutionize PJI diagnosis and management.
The risk of PJI remains unacceptably high and currently there is a large gap in our understanding of the specific pathogens that lead to this devastating complication. Furthermore, there is significant uncertainty regarding the primary source of infection, which has rendered prophylactic measures less useful. One key characteristic shared by many of the agents causing PJI, according to Costerton and colleagues, is their ability to create biofilm, a hydrated polymeric matrix that protects them from immunologic and pharmacologic insults in addition to facilitating the spread of antibiotic resistance.
|
|
Gold standard has drawbacks
A useful diagnostic modality will have the capacity to identify infections at an early stage, allowing for effective management through irrigation and debridement. Unfortunately, current diagnostic methods lack acceptable sensitivity to enable successful detection in many cases. The current gold standard for the diagnosis of infection is joint aspirate or intraoperative tissue culture. However, it takes many days to obtain these results and these tests have a characteristically low sensitivity, especially in patients who have recently been treated with antibiotics.
In the presence of these restrictions, surgeons rely on multiple diagnostic tools to identify and manage patients with suspected PJI. These include measurement of inflammatory serum markers, including C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), imaging modalities, synovial fluid analysis, or intraoperative diagnostic techniques, such as histopathological examination of the surrounding tissue, and microbiological testing.
Although Austin and colleagues consider CRP levels to be a sensitive and cost-effective screening tool, its applicability is limited in patients with underlying inflammatory conditions and it lacks the capacity to identify the causative agent. Furthermore, evaluation of PJI using plain radiographs has a characteristically low sensitivity and specificity in detecting infections, as many radiologic findings, including periprosthetic radiolucency and osteolysis are non-specific. Additionally, CT and MRI evaluations are limited by prosthetic artifacts (an issue less concerning in cases where non-ferromagnetic implants are used). Other imaging modalities, including bone scans, gallium-67 scans, indium-111 scan, and positron emission tomography scan have also been postulated as possible diagnostic modalities with characteristic limitations.
Investigating diagnostic strategies
Synovial fluid aspirations have recently shown to be a diagnostic technique with increasing importance in the detection of PJIs. Aspirated fluid can be further analyzed using differential cell count, fluid culture and enzymatic assays such as leukocyte esterase. According to Del Pozo and colleagues, current guidelines suggest a leukocyte count of more than 1.73103 with 65% neutrophils in the knee and a count of 4.23103 with more than 80% neutrophil in the hip as being suggestive of PJI. Culturing of synovial fluid is more challenging given the fastidious nature of some organisms and inhibition of culture growth in the presence of antibiotic treatment.
The limitations of the standard techniques to adequately identify and characterize many of the infective agents have significantly hampered the effective management of PJI. To address this concern, many other diagnostic strategies have been investigated. One such diagnostic approach is the use of the PCR technique, which detects bacterial-specific nucleic acid particles in the joint to identify the causative agent. A study by Tunney and colleagues comparing the sensitivity of PCR with conventional culture techniques demonstrated a sensitivity of 72% for PCR compared to a sensitivity of 22% in conventional culture techniques at the time of revision arthroplasty.
This technique utilizes the detection of the highly conserved 16S rRNA in bacteria to identify the presence of an infection. In addition to the highly conserved primer sites, there are species-specific signature sequences that further enable bacterial identification. The recent advance in isolation of RNA for diagnostic means has reduced the number of false positive test results previously associated with DNA-based PCR techniques. Furthermore, the use of PCR for detecting PJIs has shed light on the possibility that many of these infections may be polymicrobial, with many of the causative bacteria being highly fastidious and thus difficult to detect using the traditional culture techniques, according to Riggio and colleagues.
Possibilities with PCR technique
Such findings raise the possibility that many instances previously coined as aseptic failure may actually be infections by organisms that have escaped our current diagnostic capabilities. This may in part contribute to the higher infection rates seen in revision cases, further emphasizing the utility of PCR as a diagnostic tool. Furthermore, the higher sensitivity of the PCR technique can help in minimizing the use of broad-spectrum antibiotics, which currently presents a challenge in patients with negative cultures but high clinical suspicion for infection. While the use of PCR in identifying PJI remains a research endeavor, its potential utility expands beyond organism identification in that it may be able to detect known drug resistance genes, allowing for more effective pharmacological management.
The potential utility of PCR in identifying PJI is an exciting recent phenomenon. Yet, the progress in translating this technology into clinical practice has been limited by a number of factors. These include need for additional equipments, the length of time and the technical challenges associated with performing this test as well as the associated increase in costs. However, as indicated by previous studies, the advantage of using the RNA-based PCR assays remains significant, as the issues associated with DNA-based PCR assays with its higher false positive results and inherently higher sensitivity can now be largely circumvented.
References:
- Austin MS, Ghanem E, Joshi A, et al. A simple, cost-effective screening protocol to rule out periprosthetic infection. J Arthroplasty. 2008;23(1):65-68.
- Costerton, JW, Montanaro L, Arciola CR. Biofilm in implant infections: its production and regulation. Int J Artif Organs. 2005;28(11):1062-1068.
- Del Pozo JL, Patel R. Clinical practice. Infection associated with prosthetic joints. N Engl J Med. 2009;361(8):787-794.
- Riggio MP, Dempsey KE, Lennon A, et al. Molecular detection of transcriptionally active bacteria from failed prosthetic hip joints removed during revision arthroplasty. Eur J Clin Microbiol Infect Dis. 2010;29(7):823-834.
- Tunney MM, Patrick S, Curran MD, et al. Detection of prosthetic hip infection at revision arthroplasty by immunofluorescence microscopy and PCR amplification of the bacterial 16S rRNA gene. J Clin Microbiol. 1999;37(10):3281-3290.
Javad Parvizi, MD, FRCSC, can be reached at Rothman Institute of Orthopaedics at Jefferson, 925 Chestnut St., 2nd Floor, Philadelphia PA 19107; 267-399-3617; e-mail: parvj@aol.com.
