Data-driven body mass index threshold associated with increased risk of 2-year periprosthetic joint infection following total shoulder arthroplasty

Background: Body mass index (BMI) is a modifiable risk factor for medical and infectious complications following total shoulder arthroplasty (TSA). Previous studies investigating BMI were limited to the conventional classification system, which may be outdated for modern day patients. Therefore, the purpose of this study was to identify BMI thresholds that are associated with varying risk of 90 -day medical complications and 2 -year prosthetic joint infection (PJI) following TSA. Methods: A national database was utilized to identify 10,901 patients who underwent primary elective TSA from 2013 to 2022. Patients were only included if they had a BMI value recorded within 1 month prior to TSA. Separate stratum -specific likelihood ratio analyses, an adaptive technique to identify data -driven thresholds, were performed to determine data -driven BMI strata associated with varying risk of 90 -day medical complications and 2 -year PJI. The incidence rates of these complications were recorded for each stratum. To control for confounders, each BMI strata was propensity -score matched based on age, sex, hypertension, heart failure, chronic obstructive pulmonary disease, and diabetes mellitus to the lowest identified BMI strata for both outcomes of interest. The risk ratio (RR) and 95% confidence interval (CI) were recorded for each matched analysis. Results: The average age and BMI of patients was 70.5 years (standard deviation +/- 9.8) and 30.7 (standard deviation +/- 6.2), respectively. Stratum -specific likelihood ratio analysis identified two BMI strata associated with differences in the rate of 2 -year PJI: 19-39 and 40 + . The same strata were identified for 90 -day major complications. When compared to the matched BMI 19-39 cohort, the risk of 2 -year PJI was higher in the BMI 40 + cohort (RR: 2.7; 95% CI 1.39-5.29; P = .020). After matching, there was no significant difference in the risk of 90 -day major complications between identified strata (RR: 1.19, 95% CI: 0.86-1.64; P = .288). Conclusion: A data -driven BMI threshold of 40 was associated with a significantly increased risk of 2 -year PJI following TSA. This is the first TSA study to observe BMI on a continuum and observe at what point BMI is associated with increased risk of 2 -year PJI following TSA. Our identified BMI strata can be incorporated into risk -stratifying models for predicting both PJI and 90 -day major complications to minimize both.