Obesity Increases Risk of Failure to Achieve the 1-Year PROMIS PF-10a Minimal Clinically Important Difference Following Total Joint Arthroplasty

The aims of this study were to determine if increasing body mass index (BMI) is a risk factor for failure to attain the 1-year Patient Reported Outcomes Measurement Information System Physical Function (PROMIS PF-10a) minimal clinically important difference (MCID) following total joint arthroplasty (TJA) and to determine a possible BMI threshold beyond which this risk increases significantly.

This retrospective study was performed using 3506 TJAs sourced from a regional-based registry. An anchor-based MCID threshold of 7.9 was chosen. PROMIS PF-10a scores were collected at the preoperative and 1-year postoperative timepoints, and the change was used to determine failure to achieve the 1-year MCID. Demographic and surgical variables were also collected. The association between BMI and failure to achieve 1-year PROMIS PF-10 MCID was then evaluated using logistic regression. A BMI threshold was determined using receiver operating characteristic (ROC) curve analysis.

Increasing BMI assessed continuously was a significant risk factor for failure to achieve the MCID (P < .001). “Obese Class I” (30-35 kg/m²), “Obese Class II” (35-40 kg/m²), and “Obese Class III” (>40 kg/m²) subgroups compared to “Normal BMI” (<25 kg/m²) were significantly associated (P < .05) with this adverse outcome as well.

Our study showed that increasing BMI is a risk factor for failure to achieve the 1-year PROMIS PF-10a MCID following TJA. Among our patients, an increase in 1 kg/m² increased the risk of failure to achieve the MCID by 2%. With these findings, surgeons will be better equipped to preoperatively advise patients with elevated BMIs considering TJA.