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J Clin Med. 2019 May 10;8(5). pii: E650. doi: 10.3390/jcm8050650.

The W.A.I.O.T. Definition of High-Grade and Low-Grade Peri-Prosthetic Joint Infection.

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Studio Medico Cecca-Romanò, Corso Venezia, 20121 Milano, Italy.
Romano Institute, Rruga Ibrahim Rugova 1, 00100 Tirane, Albania.
Advanced Medical Center, Riyadh 12482, Saudi Arabia.
Zerktouni Orthopaedic Clinic, Casablanca 20000, Morocco.
R.R. Vreden Russian Research Institute of Traumatology and Orthopaedics, 195427 S. Petersburg, Russia.
RNIITO Department of Prevention and Treatment of Wound Infection, 195427 S. Petersburg, Russia.
Department of Orthopaedics, British Hospital Buenos Aires, Buenos Aires C1280, Argentina.
Department of Orthopaedics, October 6 University, Cairo 12566, Egypt.
Department of Paediatric Orthopaedics and Spine Surgery, Children's Orthopedic Centre, Mumbai 400016, India.
Section Injury Prevention, DGOU, 10117 Berlin, Germany.
Hull University Teaching Hospitals, Anlaby Road, Hull HU3 2JZ, UK.
Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kanazawa University, 13-1 Takara-machi, Kanazawa, Ishikawa 920-8641, Japan.
Clinical Microbiology, University of Milan, 20100 Milano, Italy.
Studio Medico Cecca-Romanò, Corso Venezia, 20121 Milano, Italy.


The definition of peri-prosthetic joint infection (PJI) has a strong impact on the diagnostic pathway and on treatment decisions. In the last decade, at least five different definitions of peri-prosthetic joint infection (PJI) have been proposed, each one with intrinsic limitations. In order to move a step forward, the World Association against Infection in Orthopedics and Trauma (W.A.I.O.T.) has studied a possible alternative solution, based on three parameters: 1. the relative ability of each diagnostic test or procedure to Rule OUT and/or to Rule IN a PJI; 2. the clinical presentation; 3. the distinction between pre/intra-operative findings and post-operative confirmation. According to the WAIOT definition, any positive Rule IN test (a test with a specificity > 90%) scores +1, while a negative Rule OUT test (a test with a sensitivity > 90%) scores -1. When a minimum of two Rule IN and two Rule OUT tests are performed in a given patient, the balance between positive and negative tests, interpreted in the light of the clinical presentation and of the post-operative findings, allows to identify five different conditions: High-Grade PJI (score ≥ 1), Low-Grade PJI (≥0), Biofilm-related implant malfunction, Contamination and No infection (all scoring < 0). The proposed definition leaves the physician free to choose among different tests with similar sensitivity or specificity, on the basis of medical, logistical and economic considerations, while novel tests or diagnostic procedures can be implemented in the definition at any time, provided that they meet the required sensitivity and/or specificity thresholds. Key procedures to confirm or to exclude the diagnosis of PJI remain post-operative histological and microbiological analysis; in this regard, given the biofilm-related nature of PJI, microbiological investigations should be conducted with proper sampling, closed transport systems, antibiofilm processing of tissue samples and explanted biomaterials, and prolonged cultures. The proposed WAIOT definition is the result of an international, multidisciplinary effort. Next step will be a large scale, multicenter clinical validation trial.


PJI; WAIOT; criteria; definition; diagnosis; infection; joint prosthesis

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