The Longitudinal Variations of Paraspinal Muscle Fatty Infiltration in Obese Patients after Bariatric Surgery

Purpose: The effect of bariatric surgery on the bone density reduction is well documented, while its effect on the paraspinal muscle remains unclear. The purpose of this study is to analyze changes in muscle fatty infiltration one year after bariatric surgery in young obese adults. Methods: Fifty-two obese patients (38 female, BMI = 43.5± 5.6 kg/m ² ) who underwent Bariatric surgery and 52 age- and sex-matched controls with normal weight (BMI = 23.5±5.6 kg/m ² ) at baseline. Forty patients came back at one-year follow-up. Quantitative Dixon and T2 mapping MRI were employed to evaluate the paraspinal muscles and intervertebral disc degeneration respectively. Fat fraction (FF) and cross-sectional area (CSA) of multifidus muscle (MF), erector spinae (ES), and psoas muscles and T2 value of intervertebral disc at various disc levels were taken and compared between patients and controls, as well as preoperatively and postoperatively for the patients. Furthermore, the correlations of these MRI variables from preoperative to the postoperative and clinical variables were explored. Pearson correlation was used to analysis the link between the variables of muscle MRI parameters and weight as well as obesity-related experimental indices from preoperative to the postoperative. Results: Obese patients exhibited increased FF values in three muscles, increased CSA in the ES at all disc levels ( P <0.001). While for the MF and psoas, only L4/5 and L5/S1 disc levels demonstrated significant increased CSA value in patient group ( P <0.05). Patient group displayed significantly lower T2 values and higher Pfirrmann classification of all the five intervertebral discs (all P < 0.05), particularly in high levels. One year postoperatively, FF values of the ES and MF significantly decreased only at L1/2-disc level ( P < 0.05). These decreases were not significantly correlated with weight loss (all P > 0.05). While a link between variables of high-sensitivity C-reactive protein and FF decrease of the ES and MF from preoperative to postoperative were evidenced ( P < 0.05). Conclusions Significant improvements in muscle fatty infiltration were observed postoperatively in the ES and MF at higher level, which may be linked to the improvements of high-sensitivity C-reactive protein.