Is BMI Outdated in TKA Patient Selection? Assessment of the Impact of Pre-tubercular Subcutaneous Tissue Thickness and the Risk of Postoperative Infection Following Total Knee Arthroplasty

While Body Mass Index (BMI) is currently used as a primary tool for risk stratification in patients undergoing Total Knee Athroplasty(TKA), its limitations raise concerns regarding its accuracy and fairness in guiding surgical decision-making. In particular, reliance on BMI alone may lead to the exclusion of patients who could safely benefit from surgery, while failing to identify others at increased risk due to unfavourable local anatomical factors. Pre-tubercular subcutaneous fat thickness (PTFT) offers a simple, reproducible, and anatomically relevant measurement that directly reflects the soft tissue envelope at the operative site. As such may provide a more clinically meaningful assessment of infection risk than BMI. This study aims to evaluate the association between PTFT and postoperative infection following TKA. By doing so, it seeks to determine whether PTFT could serve as an adjunct or alternative risk stratification tool in clinical practice. The findings of this study have the potential to inform a more individualized approach to patient selection and preoperative counselling, improving shared decision-making and resource utilisation.

Inclusion Criteria: 1. Adults aged 18 years or older at the time of surgery 2. Underwent primary total knee replacement surgery 3. Procedure performed at East Lancashire Hospitals NHS Trust (Burnley General Hospital or Royal Blackburn Hospital) 4. Surgery performed between 1 November 2023 and 30 November 2024 5. Availability of a preoperative lateral knee X-ray to allow measurement of soft tissue thickness Exclusion Criteria: 1. Patients who underwent revision knee replacement surgery 2. Patients who underwent partial (unicompartmental) knee replacement surgery 3. Patients aged under 18 years at the time of surgery 4. Primary procedure performed outside East Lancashire Hospitals NHS Trust 5. Absence of a suitable preoperative lateral knee X-ray for measurement of soft tissue thickness 6. Patients who have registered a National Data Opt-Out