The role of subcutaneous fat and BMI in predicting surgical outcomes and patient reported outcomes in robotic-assisted total hip arthroplasty.

BACKGROUND

The purpose of this study was to assess if subcutaneous fat (SCF) or BMI is a predictor of surgical complications and patient reported outcomes in patients undergoing robotic-assisted total hip arthroplasty (THA).

METHODS

Patients who underwent robotic-assisted primary THAs at one institution between 2018 and 2020 were included in this retrospective cohort study. Prior to surgery, computed tomography (CT) was used to measure SCF in the posterolateral quadrant of the hip. SCF was measured 3 centimeters (cm) proximal to the greater trochanter (PGT) and 3 cm inferior to the distal tip of the greater trochanter (DGT).Measurements were normalized to the size of the patient's bony anatomy by dividing the subcutaneous fat area measurement by the transverse diameter of the femur 10 cm inferior to the tip of the greater trochanter. Patients were divided into quintiles determined by SCF distribution around the mean (groups 1-5) and BMI (BMI<25, BMI 25-29.9, BMI 30-34.9, BMI 35-39.9, and >40). Ninety day outcomes and PROMIS (Patient Reported Outcome Measures Information System) scores were acquired from the Michigan Arthroplasty Registry Collaborative Quality Initiative (MARCQI) database preoperatively, at 14-112 days post-operative and at the latest follow up.

RESULTS

There were 175 patients identified with a mean age of 63.83 years (range 27-89) and a mean BMI of 30.73kg/m2 (range 18.2-48.4). Interclass correlation coefficient was greater than 0.9 in all PGT, DGT, and GT measurements. Analysis of Variance (ANOVA) found there was a significantly shorter time from incision to closure in quintiles 1 and 3 when compared to the SCF quintile 5 (p<0.05) and that there was a significantly shorter time from incision to closure in BMI categories 1, 2, and 3 when compared to BMI category 5 (BMI > 40). There were no differences between SCF and BMI as predictive of length of stay, transfusion status, infection, or PROMIS scores.

CONCLUSION

It can be concluded that hip SCF on axial CT images can reliably measure SCF and is predictive of time from incision to closure, but it does not show a significant difference in predicting the length of stay, infection, or PROMIS scores when compared to BMI.