Paper of the Week: Determining Diagnostic Thresholds for Acute Postoperative Periprosthetic Joint Infections

Kamolsak Sukhonthamarn, MD, Timothy L. Tan, MD, Chi Xu, MD, Feng-Chih Kuo, MD, Mel S. Lee, MD, Mustafa Citak, MD, PhD, Thorsten Gehrke, MD, Karan Goswami, MD, and Javad Parvizi, MD, FRCS

The Journal of Bone and Joint Surgery: September 22, 2020
DOI: 10.2106/jbjs.20.00257 PMID: 32941311 

Summary by: Francis J Sirch IV, BS

Periprosthetic joint infection (PJI) is a common complication of TJA with an estimated incidence of 2% , and is the third leading cause of primary failure.1 Traditionally, diagnosis of chronic PJI is dependent on clinical presentation, as well as serum biomarkers such has erythrocyte sedimentation rate (ESR), c-reactive protein (CRP), and synovial fluid testing.2 In 2018, the second international consensus meeting (ICM) on musculoskeletal infection developed new criteria for the diagnosis of PJI that was later validated to have better accuracy, sensitivity and specificity than prior definitions.3 However, the cohorts used in the external validation utilized chronic infections which may limit its application to acute PJI. Despite improved diagnostic guidelines, diagnosing acute PJI remains difficult due to early post-surgical inflammatory signaling that make interpretation of biochemical marker profiles challenging.4 

In this study, Sukhonthamarn et al explored the diagnostic thresholds of serum CRP, ESR, synovial fluid WBCs, and polymorphonuclear neutrophil (PMN) percentage in the diagnosis of acute PJI.  They retrospectively reviewed 197 patients with suspected PJI who had been evaluated within 90 days of their index procedure. This cohort was further divided into 123 patients with confirmed PJI, and 74 patients in which PJI was ruled out. This study found that synovial fluid profiles and serum biomarkers were all significantly elevated in the infected group compared to non-infected group (p <0.05). Mean value of synovial fluid WBC count was 54,780 cells/uL for the PJI group and 4,130 cells/uL for the non-infected group (p <0.001). PMN percentage was found to be 90.2% in infected group compared to 70.5% in non-infected group (p = 0.03) , serum CRP was 114 mg/L in infected group and 29 mg/mL in control group (p = <0.001), and ESR was 71.6 mm/hr in infected group and 31.33 mm/hr in non-infected group (p <0.001). The ROC curve analysis demonstrated that synovial fluid WBC count was the best diagnostic test with an AUC of .96, followed by serum CRP (AUC, .94), ESR (AUC, 0.83), and synovial fluid PMN percentage (AUC, 0.79). An optimal threshold for cutoff level was found to be synovial fluid WBC of 6,310 cell/uL, which was shown to have sensitivity of 90.9% and specificity of 82.6%.

The authors of this study concluded that current thresholds used by the MSIS and ICM criteria have poor sensitivity, and that optimal cutoffs should be lower than previous studies have suggested. The prior ICM and MSIS defined an acute PJI as 90 days after an index procedure, however the authors argue that infection is better represented as a continuum. Additionally, the authors suggest that these new cutoffs for the diagnosis of PJI are joint-independent as knee and hip arthroplasty have similar thresholds of diagnosis. Limitations of this study include that it was retrospective in nature, lacks a consensus on time cutoffs to define acute vs chronic infection, difficulty in defining non-infected groups due to other complications, and influence of autoimmune inflammatory disease’s impact on serum biomarkers.


1. Parvizi, J., Fassihi, S. C. & Enayatollahi, M. A. Diagnosis of Periprosthetic Joint Infection Following Hip and Knee Arthroplasty. Orthop Clin N Am 47, 505–515 (2016).

2. Parvizi, J. et al. The 2018 Definition of Periprosthetic Hip and Knee Infection: An Evidence-Based and Validated Criteria. J Arthroplasty 33, 1309-1314.e2 (2018).

3. Shohat, N. et al. Hip and Knee Section, What is the Definition of a Periprosthetic Joint Infection (PJI) of the Knee and the Hip? Can the Same Criteria be Used for Both Joints?: Proceedings of International Consensus on Orthopedic Infections. J Arthroplasty 34, S325–S327 (2018).

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