Septic revision TKA patients included in the study. These are patients who are considered infected according to Musculoskeletal Infection Society criteria for infection.

Calprotectin test: Calprotectin will be measured both by ELISA and point of care test.

Total of all reporting groups

The Charlson Comorbidity Index is a method of categorizing comorbidities of patients based on the International Classification of Diseases (ICD) diagnosis codes found in administrative data, such as hospital abstracts data. Each comorbidity category has an associated weight (from 1 to 6), based on the adjusted risk of mortality or resource use, and the sum of all the weights results in a single comorbidity score for a patient. Points are additionally added for age based on decade of life. A score of zero indicates that no comorbidities were found. Minimum is 0. Max is 27.

An erythrocyte sedimentation rate (ESR) is a type of blood test that measures how quickly erythrocytes (red blood cells) settle at the bottom of a test tube that contains a blood sample. Normally, red blood cells settle relatively slowly. A faster-than-normal rate may indicate inflammation in the body.

ESR was not collected for primary TKA as it is not standard of care ESR was not ordered by the physician for 2 septic cases

C-reactive protein (CRP) is a protein made by the liver. CRP levels in the blood increase when there is a condition causing inflammation somewhere in the body. A CRP test measures the amount of CRP in the blood to detect inflammation due to acute conditions or to monitor the severity of disease in chronic conditions.

CRP was not collected for primary TKA as it is not standard of care CRP was not ordered by the physician for the 1 septic case

Synovial WBC was not collected for primary TKA as it is not standard of care Synovial WBC was unable to be run due to insufficient quantity for the 1 septic case

Synovial PMN% was not collected for primary TKA as it is not standard of care Synovial PMN% was unable to be run due to insufficient quantity for 2 septic cases

Low Risk is defined 0-14 mg/L Medium Risk is defined as 14-50 mg/L High Risk is defined as >50 mg/L

The risk refers to risk of PJI

Low Risk is defined 0-14 mg/L Medium Risk is defined as 14-50 mg/L High Risk is defined as >50 mg/L

The risk refers to risk of PJI

A tunneling wound or sinus tract is a narrow opening or passageway extending from a wound underneath the skin in any direction through soft tissue and results in dead space with potential for abscess formation.

This was observed during surgery and collected from the operative note. This is not an outcome measure, rather it is used to assist in classifying a case as septic or aseptic using the Musculoskeletal Infection Society criteria for PJI. By definition all patients with a sinus tract are septic, however not all septic cases have a sinus tract.

MSIS criteria was only applied to septic and aseptic cases.

Cultures were not ordered on primary TKAs as they are not standard of care

Histopathology was not ordered on primary TKAs as they are not standard of care.

It was not ordered for a number septic and aseptic cases due to the individual preferences of the surgeon.

There will be n=50 septic revision TKA patients included in the study. These are patients who are considered infected according to Musculoskeletal Infection Society criteria for infection.

Calprotectin test: Calprotectin will be measured both by ELISA and point of care test.

ELISA analysis

Area under the curve (AUC) was calculated using receiver operator characteristic (ROC) curve using the two cut offs (>14 mg/L and >50 mg/L) for both the ELISA and POC tests. Data were collected intraoperatively during the patient's arthroplasty surgery.

AUC - ROC curve is a performance measurement for classification problem at various thresholds settings. ROC is a probability curve and AUC represents degree or measure of separability. It tells how much model is capable of distinguishing between classes. Higher the AUC, better the model is at predicting 0s as 0s (aseptics that are negative) and 1s as 1s (septics that are positive). 1.000 represents accurately predicting each aseptic as negatve and each septic as positive. While a 0.000 represents accurately predicting each aseptic as positive and each septic as negative.

Primary TKAs were no analyzed as AUC is a binary analysis representing the accuracy of predicting the correct diagnosis, ie (an aseptic is an negative, or a septic is positive). Arms/Groups are combined as the data represents the accuracy of all septics and aseptics combined at a given threshold for either the POC or ELISA test. This assessment was pre-specified to combine Arms.

There will be n=70 aseptic revision TKA patients included in the study. These are patients who are not considered infected according to Musculoskeletal Infection Society criteria for infection.

Calprotectin test: Calprotectin will be measured both by ELISA and point of care test.

There will be n=50 septic revision TKA patients included in the study. These are patients who are considered infected according to Musculoskeletal Infection Society criteria for infection.

Calprotectin test: Calprotectin will be measured both by ELISA and point of care test.

Sensitivity was calculated using 2x2 tables using >14 mg/L cut off. Sensitivity is the number of septic positives over the number of septics.

Sensitivity was calculated using 2x2 tables using >50 mg/L cut off. Sensitivity is the number of septic positives over the number of septics.

Positive predictive value was calculated using 2x2 tables using >14 mg/L cut off. The numerator is the septic positives and the denominator are the total positives.

Positive predictive value was calculated using 2x2 tables using >50mg/L cut off. The numerator is the septic positives and the denominator are the total positives.

Negative predictive value was calculated using 2x2 tables using >14 mg/L cut off. The numerator is the aseptic negatives and the denominator is the number of total negatives.

Negative predictive value was calculated using 2x2 tables using >50 mg/L cut off. The numerator is the aseptic negatives and the denominator is the number of total negatives.

Negative predictive value was calculated using 2x2 tables using >50 mg/L cut off. NPV=98.5%