Marlene Busko

October 16, 2015

SEATTLE — In a large, retrospective, cohort study of mainly middle-aged, obese women in the province of Quebec who had bariatric surgery, the patients had a 20% higher risk of a fracture after the operation, and the fractures usually occurred after a few years.

Intriguingly, before they had bariatric surgery, the patients were more likely to have fractures of the knee, foot, ankle, tibia, and fibula (lower extremities) that are typical for obese individuals, but 4 or more years after having the bariatric procedure, they were more likely to have fractures at sites that are typical for osteoporosis.

Those who had bariatric surgery had a twofold higher risk of having a fracture in the shoulder, humerus, elbow, forearm, or wrist (upper extremities) and a threefold higher risk of having a fracture in the hip, femur, or pelvis, compared with control patients.

There was no change in the number of spinal fractures (also characteristic of osteoporosis), but there were very few such fractures in this cohort overall, said Catherine Rousseau, medical school student at Laval University, in Quebec City, who reported these findings in an oral presentation and in a poster that won a Young Investigator Award, at the recent American Society for Bone and Mineral Research (ASBMR) 2015 Annual Meeting.

She speculated that the shift in fracture sites after bariatric surgery may be because obese individuals fall differently, or nutrient deficiencies after bariatric surgery affect bone mass, or weight loss may lead to increased physical activity and therefore a greater risk of traumatic fractures, among other reasons.

However, the database lacked important information, for example, about body mass index (BMI) and type of bariatric surgery, she acknowledged, in reply to questions following her presentation. More research is urgently needed to better inform clinical practice, the researchers say.

In the meantime, "the take-away message is that fracture risk assessment should be part of postoperative clinical care [of patients who undergo bariatric surgery, since] those patients…are a high-risk group for fractures," Ms Rousseau told Medscape Medical News.

"Potentially reversible factors that accelerate bone loss should be aggressively treated," she and her colleagues said.

Weaker Bones, More Breaks After Bariatric Surgery?

Obese patients who undergo bariatric surgery appear to lose bone mass and have changes in bone metabolism, but their risk of fracture is unclear, Ms Rousseau and colleagues explained as background.

To investigate this, they analyzed data from 10,662 individuals, mainly women (72.6%), with a mean age of 42 years, who had bariatric surgery from 2001 to 2012 in the Canadian province of Quebec. The patients were matched for age and sex with 31,986 obese individuals and 31,986 nonobese individuals who did not have bariatric surgery.

The patients had follow-up data for a mean of 4.2 years (from less than 1 to 12 years).

Individuals who had bariatric surgery were more likely to live in small towns, be socially disadvantaged, and have more comorbidities (including hypertension, diabetes, and cardiovascular disease) and a history of fracture, but they were less likely to have a diagnosis of osteoporosis.

Patients in the surgery group had a first fracture a mean of 3.6 years (range, 1.6 to 5.1 years) after their bariatric procedure.

In the follow-up period after surgery, 3.9% of the bariatric patients but only 2.6% of the obese control patients and 2.3% of the nonobese controls had a fracture (P < .0001).

The risk of a fracture was significantly higher for patients who had bariatric surgery compared with nonobese control patients (relative risk [RR], 1.45) or obese controls (RR, 1.36), after adjustment for age, socioeconomic status, and comorbidities.

The relative risk of having a fracture was 1.19-fold higher after vs before surgery in the patients who underwent bariatric procedures, but the risk remained unchanged in the two control groups.

A Threefold Increase in Pelvic, Hip, or Femur Fractures

Ms Rousseau and colleagues next investigated whether the fractures in patients who underwent bariatric surgery were in the upper or lower extremities or a central (spine, hip, pelvis, or femur) part of the body.

After surgery, patients had a 33% lower risk of a fracture of the knee, foot, ankle, tibia, or fibula (lower extremity) but a heightened risk of an upper-extremity fracture (shoulder, humerus, elbow, forearm, or wrist) or a central fracture (spine, hip, femur, or pelvis).

Ms Rousseau acknowledged that study shortcomings, related to the database, included a lack of information about BMI, type of bariatric surgery, and fall- and fracture-related factors such as medication, smoking status, alcohol consumption, physical-activity level, vitamin D status, calcium intake, menopausal status, and family history of fractures.

However, this was a large, representative sample of patients undergoing recent bariatric surgery in this province, she said, and they had two control groups.

The data are "interesting, but I think the limitation of an absence of BMI is really important," said a member of the audience. He wondered "if someone [has a BMI of] 40 and gets down to [a BMI of] 27, do they have the same fracture risk of someone whose [BMI is] 27, or do they have a [greater] fracture risk? You have to be really careful about claiming that these patients have an additional risk factor," he said, a point with which Ms Rousseau agreed.

Plans to Investigate Risk Related to Type of Surgery

Another attendee wanted to know if the incidence of fractures was higher with age and related to menopausal status. Ms Rousseau replied that the patients who had fractures tended to be 1 or 2 years older than average.

It would have been good to know which patients had gastric banding vs other bariatric surgeries that lead to malabsorption of nutrients, another person commented.

Ms Rousseau said they have this information only for more recent surgeries from 2006 onward, and they plan to investigate this group of patients. "In Quebec, gastric banding is decreasing, and there is an increase of malabsorptive surgeries and sleeve gastrectomy," she noted.

American Society for Bone and Mineral Research 2015 Annual Meeting; Seattle, Washington. Abstract FR0361, presented October 9, 2015; Abstract 1073, presented October 10, 2015.


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