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Gastric bypass surgery associated with increased fracture risk

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August 3, 2018

Adults with obesity who undergo Roux-en-Y gastric bypass surgery are more likely to sustain a fracture independent of the amount of weight loss or diabetes status, with the risk for fracture rising over time, according to a study published in the Journal of Bone & Mineral Research.

“While sleeve gastrectomy recently has risen to become the choice, Roux-en Y gastric bypass is still the historically most utilized method, the most effective and well-documented bariatric procedure, providing long-term weight loss, metabolic benefits and improved survival,” Kristian F. Axelsson, MD, MSc, of the department of orthopedic surgery at Skaraborg Hospital, Skövde, Sweden, and colleagues wrote in the study background. “However, gastric bypass surgery has adverse effects on the skeleton, as reflected by increase bone resorption markers and decreased bone mineral density post-surgery.”

In a retrospective cohort study, researchers analyzed data from 38,971 adults with a baseline BMI of at least 30 kg/m² who underwent Roux-en-Y gastric bypass, identified through the Scandinavian Obesity Surgery Register. This register consisted of data on pre-surgery weight and height data, along with follow-up measurements at 6 weeks, 12 and 24 months, and HbA1c. Two different registers were used to identify patients with obesity not undergoing gastric bypass (controls). Within the cohort, 7,727 patients had diabetes. 

Researchers used propensity score matching to match gastric bypass patients with diabetes with controls with diabetes, as well as to compare non-diabetic gastric bypass patients with controls without diabetes, adjusting for baseline characteristics. Median follow-up time was 3.1 years.

Among patients with diabetes who underwent gastric bypass, mean weight loss was 17.4 kg at 6 weeks, 35.5 kg at 12 months and 35.1 kg at 24 months. Among gastric bypass patients without diabetes, the mean weight loss was 17.6 kg at 6 weeks, 39.3 kg at 12 months and 39.9 kg at 24 months. Among control patients with diabetes, 4,513 (58%) presented 1 year after baseline with slight weight loss (mean, 117.7 kg) vs. baseline (mean, 119.9 kg; P < .001).

In an unadjusted Cox model, researchers observed an association between gastric bypass surgery and any fracture in patients with obesity, regardless of diabetes status. The HR for patients for fracture for those with diabetes was 1.26 (95% CI, 1.04-1.52), whereas the HR for fracture for those without diabetes was 1.31 (95% CI, 1.17-1.46), with the correlation persisting after multivariable adjustment.

Researchers also observed an increase in the risk for major osteoporotic fracture, independent of diabetes status, whereas patients without diabetes had a higher risk for arm fracture and a  lower risk for lower leg fracture. Gastric bypass patients without diabetes had a decreased risk for any fracture in the first year after surgery; however, researchers observed a gradual increase in fracture risk independent of diabetes status.

Multivariable Cox models revealed a lower mortality risk in gastric bypass patients with (47%) and without diabetes (45%) vs. controls. Conversely, the risk for fall injury with no fracture was higher in gastric bypass patients both with (HR = 1.26; 95% CI, 1.04-1.52) and without diabetes (HR = 1.24; 95% CI, 1.12-1.38) vs. controls. No correlation was observed between greater weight loss or vitamin D supplementation and fracture risk, according to researchers.

“Gastric bypass surgery is associated with an increased fracture risk, which appears to be increasing with time and not associated with degree of weight loss or calcium and vitamin D supplementation following surgery,” the researchers wrote. “An increased risk of fall injury was seen after surgery, which could contribute to the increased fracture risk.”by Jennifer Byrne

Disclosure: Axelsson reports he has received lecture fees from Amgen, Lilly and Meda/Mylan. Please see the study for the other authors’ relevant financial disclosures.