Incidence and Microbial Profiles of Periprosthetic Joint Infection After Total Knee Arthroplasty in Obese vs Non-Obese Patients

Importance: After a primary total knee arthroplasty (TKA), we anticipate that obese individuals are more likely to experience a of periprosthetic joint infection (PJI). Knowing the microbial profile in obese patients can potentially help in choosing the proper prophylactic measures for this group as well as tailoring the empirical antibiotics in relation to PJI in obese patients.

Objective: To compare incidence of PJI revisions within 2 years after TKA in obese vs non-obese OA patients. Secondarily: To compare microbial profiles of infections in these groups in two time windows: early (≤90 days) vs late (91-730 days) and incidence of revisions due to all causes within 2 years.Design and Setting: We will include patients having primary knee arthroplasty using Danish national registers. Patients will be stratified into anthropometric groups, referred to as exposed and unexposed to obesity, based on their baseline Body Mass Index (BMI). Participants included in the analysis population will be followed up for 2 years, until first revision, death or migration whichever comes first.

Participants: We will include adult patients with available weight and height data with primary/idiopathic or secondary (due to meniscus or cruciate ligament lesion) OA who received primary TKA in the period from 2011-01-01 and 2021-02-28. Patients will be identified from the Danish knee arthroplasty register.

Exposure and Comparator: The cohort will be divided into obese (exposed), defined as body mass index (BMI) ≥ 30 kg/m2; and non-obese (unexposed), defined as BMI < 30 kg/m2.

Main Outcomes and Measures: The primary outcome will be revision due to prosthetic joint infection (PJI) within 730 days following TKA. Secondary endpoints will then be to examine revision due to all causes within 730 days following TKA and type of microbial infection between obese and non-obese in the first 90 days and the period from 91 days to 730 days following TKA.

Planned Statistical Analyses: We will use descriptive statistics to summarize the baseline characteristics of the two groups. Hazard ratios with corresponding two-sided 95% confidence intervals (95%CIs) for experiencing the outcome will be estimated using a Cox proportional hazards regression model. We will fit both unadjusted (crude) model and a propensity score adjusted model calculated based on age, sex, highest completed education, household income, comedications, and Elixhauser Comorbidity Measure (ECM), all collected up to the day of surgery. Stratified analyses will categorize PJI cases by bacterial infection and compare crude proportions between groups based on the absolute risk difference with 95% confidence intervals.

Ethical Considerations and Registration: The study and its statistical analysis plan will be registered in clinicaltrials.org prior to conducting the study.

Study Overview

• Status: Completed
• Conditions: Knee Arthropathy; PJI

• Study Type: Observational
• Enrollment (Actual): 101299

Contacts and Locations

Study Locations

• Denmark
  • Copenhagen NV, Denmark, 2400
    • Department of Orthopedic surgery and traumatology, Bispebjerg Hospital, Copenhagen, Denmark

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

In order to be eligible, we will include adult patients with primary or secondary osteoarthritis (due to meniscus or cruciate ligament lesion) who underwent primary TKA between January 1, 2011, and February 28, 2021, and for whom weight and height data are available. Patients will be identified from the DKR. Patients are followed for 2 years, until first revision, death or migration, whichever comes first.

Description

Inclusion Criteria:

• Adults with available BMI data recieved knee arthroplasty due to osteoarthritis

Exclusion Criteria:

-

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort
Patients with obesity; Patients with body mass index of 30 or more
Patients without obesity; Patients with body mass index less than 30

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Incidence Periprosthetic joint infection	PJI: our definition of PJI is adapted from The European Bone and Joint Infection Society (EBJIS) criteria as at least one of the following: A. Danish Knee Arthroplasty Register-registered revision surgery due to infection. B. At least 2 deep-tissue samples of phenotypically indistinguishable bacteria isolated from at least 3 deep-tissue samples C. One or more positive intraoperative samples from a closed fluid aspirate AND a biopsy (fluid AND tissue) of phenotypically indistinguishable bacteria isolated.	2 years

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Incidence of Revision due to all causes	Any registered surgery in the ipsilateral knee following the primary arthroplasty extracted from the danish knee arthroplasty register	2 years
Proportions Microbiological profiles in periprosthetic infection	For the revision due to PJI, we will stratify the outcome looking into the proportions of the following groups of bacteria A. PJI due to Staphylococcus aureus. B. PJI due to Coagulase-negative staphylococci. C. PJI due to other gram-positive bacteria. D. PJI due to gram-negative bacteria. E. PJI due to anaerobic bacteria. F. PJI due to mycoplasmic infection. G. PJI due to polymicrobial infection. H. PJI with negative culture.	90 days
Proportions of Microbiological profiles in periprosthetic infection	For the revision due to PJI, we will stratify the outcome looking into the proportions of the following groups of bacteria A. PJI due to Staphylococcus aureus. B. PJI due to Coagulase-negative staphylococci. C. PJI due to other gram-positive bacteria. D. PJI due to gram-negative bacteria. E. PJI due to anaerobic bacteria. F. PJI due to mycoplasmic infection. G. PJI due to polymicrobial infection. H. PJI with negative culture.	91 days to 2 years

Collaborators and Investigators

• Sponsor: Bispebjerg Hospital

Study record dates

Study Major Dates

• Study Start (Actual): January 1, 2025
• Primary Completion (Actual): November 25, 2025
• Study Completion (Actual): November 25, 2025

Study Registration Dates

• First Submitted: September 25, 2025
• First Submitted That Met QC Criteria: February 2, 2026
• First Posted (Actual): February 10, 2026

Study Record Updates

• Last Update Posted (Actual): February 10, 2026
• Last Update Submitted That Met QC Criteria: February 2, 2026
• Last Verified: September 1, 2025

More Information

Terms related to this study

• Keywords: obesity; knee arthroplasty; microbiological profiles; pji
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Overweight; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Obesity; Juvenile polyposis syndrome
• Other Study ID Numbers: p-2023-14433-Micro

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No