SLR - July 2019 - Rebecca R. Calder

Fat Mass, But Not Fat-Free Mass, Predicts Increased Foot Pain with Obesity, Independent Of Bariatric Surgery
Reference: Walsh TP, Quinn SJ, Evans AM, Yaxley A, Chisholm JA, Kow L, Shanahan EM. Fat Mass, But Not Fat-Free Mass, Predicts Increased Foot Pain with Obesity, Independent Of Bariatric Surgery Surg Obes Relat Dis. 2018 Sep;14(9):1389-1395

Scientific Literature Review
Reviewed By: Rebecca R. Calder, DPM
Residency Program: MetroWest Medical Center – Framingham, MA
Podiatric Relevance: When overweight patients have foot pain it is a common hypothesis, that if patients lose weight, their foot pain will decrease. This is under the assumption the foot pain stems from a mechanical etiology and excess weight puts more stress and strain on tissues. However, is the mechanical aspect of excess tissue the true issue, or is there also a metabolic component stemming from the type of tissue which adds to the pain?  We use BMI (body mass index) to classify obesity, but is BMI a true predictor of foot pain? Or is body composition and changes in adipokines predictors in changes of foot pain following bariatric surgery?  Having concrete evidence allows for a more knowledgeable discussion with obese patients in guiding the treatment of their foot pain.
Methods: A prospective observational study was conducted between January 2015 and June 2017 and included patients on a surgical waiting list for bariatric surgery with foot pain for three months or longer.  Inclusion criteria was 18 years or older and three months or more of moderate or greater foot pain measured on the visual analog scale. Exclusion criteria was peripheral neuropathy, infectious disease, cancer, systemic inflammatory condition or previous bariatric or foot surgery. Patients underwent dual-energy x-ray absorptiometry to determine fat mass and fat-free mass at baseline and six months follow-up. Foot pain and disability was assessed with the Manchester-Oxford foot questionnaire. Data was analyzed using two multivariable linear regressions, BMI or FMI (fat mass index) and FFMI (fat-free mass index) with dependent variable foot pain at follow-up and independent variables including baseline foot pain, age, sex, group, depression and BMI or FMI and FFMI. Adipokines were measured and partial correlation was used to determine if change in adipokines were associated with change in foot pain.
Results: Forty-five patients were included in this study, twenty-nine who underwent bariatric surgery and sixteen in the control group who did not undergo bariatric surgery. After adjusting for variables, bariatric surgery was found to be a predictor of decreasing foot pain. BMI was not specifically a predictor but FMI was found to be a predictor. There was no correlation for change in adipokines leptin or adiponectin but a negative correlation was found between change in resistin and change in foot pain.  
Conclusions: The results of this study concluded bariatric surgery leads to a reduction of foot pain at a 6 month follow-up. It also concluded body composition is a better predictor than BMI and therefore reduction of weight alone may not decrease foot pain compared to reducing FMI. This study concluded FMI may be the link to obesity and pain, and therefore mechanical factors may not be the only etiology of foot pain but rather metabolic factors contribute as well. This study can change the discussion between the patient and doctor by providing guidance when treating foot pain in obese patients.

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