Category: potw

Paper of the week: Propidium monoazide-polymerase chain reaction for detection of residual periprosthetic joint infection in two-stage revision. Askar M, Sajid M, Nassif Y, Ashraf W, Scammell B, Bayston R. Mol Biol Rep. 2019 Oct 5. doi: 10.1007/s11033-019-05092-z.

Summary by Dr Sreeram Penna

In this study, researchers compare the efficacy of propidium monoazide-polymerase chain reaction (PMA-PCR or Viability PCR) for detecting residual periprosthetic joint infection in two-stage revision to a traditional polymerase chain reaction (PCR) and cultures. According to the authors, pre-treatment of propidium monoazide improves efficacy PCR testing by binding to residual DNA and RNA from the sample. Also, propidium monoazide does not cross the bacterial cell membrane and therefore, does not affect DNA from viable bacteria. Based on these actions authors postulate that by inhibiting residual DNA from both dead bacteria and human DNA in a sample using propidium monoazide, the overall efficacy of PCR in diagnosing infection is increased.

Cohort consists of 60 episodes of care in 58 patients. 14 of these episodes were considered infected using Muskulo Skeletal Infection Society criteria. The PCR assay done included only genus-specific primers for staphylococci and enterococci and species-specific primers for Cutibacterium acnes. Results showed that sensitivity of culture, PCR, and PMA-PCR were 50%, 71%, and 79%, respectively, and specificities were 98%, 72%, and 89%, respectively. Authors note that the increase in sensitivity of PMA-PCR compared to traditional PCR is due to the removal of large quantities of residual free-floating human DNA present in the sample by PMA.

In conclusion, PMA-PCR is better than traditional PCR with increased specificity and sensitivity. However, further research with broader PCR panel, including all possible bacteria causing PJI and larger sample size is needed.

Paper of the week: Plasma Viscosity Has a Role in the Diagnosis of Prosthetic Joint Infection After Total Knee Arthroplasty. Bajada S, Yoong AWH, Hourigan P, Koopmans PC, Phillips JRA, Toms AD. J Arthroplasty. 2019 Jul 30. pii: S0883-5403(19)30719-3. doi: 10.1016/j.arth.2019.07.035.

Summary by Dr Sreeram Penna

This retrospective study aimed to find out the clinical value of plasma viscosity in the diagnosis of periprosthetic joint infection (PJI) in painful total knee arthroplasty patients. Primarily researchers compared value of plasma viscosity with erythrocyte sedimentation rate (ESR) and c reactive protein (CRP). Patients with inflammatory arthropathies and lymphoproliferative disorders were excluded from the study. Researchers used MSIS criteria for diagnosing infection.

The results of the study showed that there is a strong correlation between plasma viscosity and ESR and CRP. Based on the study data, plasma viscosity value of 1.81 mPa.s. had the best efficacy. Utilizing this value sensitivity, specificity, positive likely hood ration, and negative likely hood ratio of plasma viscosity in PJI was 58.3%, 93.8%, 9.43, and 0.44, respectively. When comparing plasma viscosity to ESR in patients with both serum investigations available (107 patients), the area under the curve (AUC) was 0.814 for plasma viscosity while AUC for ESR was 0.812 — showing that PV is noninferior to ESR as a reliable screening test.

The advantages of plasma viscosity compared to ESR as suggested by authors include plasma viscosity not influenced by hematocrit (anemia, polycythemia), red blood cell aggregation, hemoglobinopathies, anti-inflammatory medication, or time to analysis, patients age. In addition, the authors mention that the plasma viscosity test is cheaper than ESR and CRP.  

Paper of the week: Periprosthetic joint infection in aseptic total hip arthroplasty revision. Renard G, Laffosse JM, Tibbo M, Lucena T, Cavaignac E, Rouvillain JL, Chiron P, Severyns M, Reina N. Int Orthop. 2019 Jun 25. doi: 10.1007/s00264-019-04366-2.

Summary by Dr Sreeram Penna

Aim of this retrospective study was to evaluate incidence of occult infection in presumed aseptic total hip arthroplasty revisions and to identify associated risk factors. Researchers retrospectively reviewed all patients who underwent aseptic total hip revision between 2009 and 2013. Total of 523 cases (498 patients) were identified. The main indications for revision were aseptic loosening(283/523, 54%), instability (91/523, 17%), periprosthetic fracture (56/523, 11%), wear and osteolysis (35/523, 7%), unexplained pain (12/523, 2%), implant fracture (13/523, 3%), and others (metallosis, squeaking, tumour, aseptic lymphocyte-dominated vascular-associated lesion, psoas impingement)(33/523, 6%). Unexpected positive cultures (UPC) were found in 78 cases (15%). Of these 58 cases were monomicrobial, and 20 cases polymicrobial. Further review identified 36 cases (7%) with positive cultures as true infections and other 42 cases (8%) as contaminants. Infection was identified in 15/91 (16%) cases who underwent revision for instability. Similarly, incidence of infection was 12% in patients with periprosthetic fracture, 3.2% in aseptic loosening and 2.8% in polyethylene wear and osteolysis group. On further analysis researchers found statistically significant difference in early dislocation (with in 3 months) rates in infection group (31%) compared to non-infection group (7%) (p<0.001).

Paper of the week: Use of incisional vacuum-assisted closure in the prevention of postoperative infection in high-risk patients who underwent spine surgery: a proof-of-concept study. Dyck BA, Bailey CS, Steyn C, Petrakis J, Urquhart JC, Raj R, Rasoulinejad P. J Neurosurg Spine. 2019 May 10:1-10. doi: 10.3171/2019.2.SPINE18947.

Summary by Dr Sreeram Penna

In this study researchers wanted to see if use of incisional vacuum assisted closure resulted in lower surgical site infections in high-risk patients who underwent spine surgery. A total of 64 patients were included In this proof of concept study. 21 patients received incisional vacuum assisted closure and and 43 diagnosis matched patients received standard dressings. Patients undergoing vacuum assisted closure met criteria for high risk of infection including posterior open surgery across the cervicothoracic junction; thoracic kyphosis due to metastatic disease; high-energy trauma; or multilevel revision reconstructive surgery. They also met one or more co-morbidity criteria, including body mass index 35 more, body mass index below 18.5, diabetes, previous radiation at surgical site, chemotherapy, steroid use, bedridden state, large traumatic soft-tissue disruption, or immunocompromised state. Although not statistically significant (p=0.314) vacuum assisted closure had lower infection rate 10% (2/21) compared to standard dressings 21% (9/43). This study demonstrates possible utility of vacuum assisted closure to reduce surgical site infections in high risk spine surgery patients.