Definition of Septic vs. Aseptic Revision

Patients were classified as undergoing septic revisions if they had definitive evidence of PJI defined as major criteria by Musculoskeletal Infection Society (MSIS)⁵.We excluded acute PJI defined as occurring less than 3 months from the index surgery and acute hematogenous PJI defined as acute symptoms occurring for less than 6 weeks but more than 3 month from index surgery.

Aseptic revisions were considered as those undergoing single stage revision who did not meet MSIS criteria with a diagnosis other than infection (loosening/wear, instability, malalignment, metallosis or other unexplained pain), nor had any further reoperation on the same joint within one year of follow-up. The reasons for aseptic revisions were loosening/wear (73.48%), instability (15.90%), malalignment (3.78%), metalosis (3.03%), and other unexplained pain (3.78%). A comparison of patient characteristics and inflammatory markers between the two groups is presented in Table ​Table1.1. We were interested in testing the value of clinical presentation on infected patients in whom it is difficult to reach a diagnosis of infection using serum and synovial markers. It has been previously shown that MSIS is a specific tool but lacks sensitivity with up to 30% underdiagnoses. ¹⁵We were able to isolate a subgroup of patients who did not meet MSIS criteria for PJI (major or minor) but were still operated on for suspected PJI (n=81).Patients without serum or synovial markers available were excluded (n=46). This information was used to evaluate the effect clinical presentation has on post-test probability.

Demographics and inflammatory markers of patient undergoing septic compared to aseptic total knee revision.

Years (yr); Kilogram (Kg); Meter (m); American Society of Anesthesiologists (ASA); Celsius (°C); Erythrocyte Sedimentation Rate (ESR); C-Reactive Protein (CRP); White Blood Cells (WBC); Polymorphonuclear Leukocytes (PMN); Synovial Fluid White Blood Cells (sWBC); Synovial Fluid Polymorphonuclear Leukocytes (sPMN); Millimeter (mm); Hour (hr); Milligram (mg); Microliter (µL). *Information on ASA was available for 101 patients in the septic group. ◦Current revision is following a primary or revision surgery