Physician Update

Elizabeth Haglind, M.D., endocrinologist discusses a Mayo Clinic study recently presented at the 2009 Endocrinology Society Annual Meeting in Washington, D.C.

Abstract
Introduction: There is a dramatic and sustained increase in bone turnover following bariatric surgery. However the impact on fracture rates is unknown. We hypothesized that accelerated bone turnover would increase fracture risk following bariatric surgery. The current study examines the fracture rate in subjects who have undergone bariatric surgery in comparison to population based age- and sex- matched controls.

Material and Methods: Using resources of the Rochester Epidemiology Project, we have currently completed a retrospective chart review in 97 of 292 subjects who underwent bariatric surgery during 1985-2004 at Mayo Clinic, Rochester. We abstracted data on the type of bariatric surgery, anthropomorphic indices over time, lifestyle and nutritional status, fracture details including date, site and mechanism of injury.

Statistical analyses: Standardized Incidence ratios (SIR) compare observed site-specific fractures to the number expected in this cohort during their follow-up. Expected numbers of fractures were derived by applying age- & sex- specific incidence rates from the local population for these fractures to the age- & sex- specific person-years of follow-up. 95% CI for the SIR were calculated by assuming that the expected rates are fixed and the observed fractures follow a Poisson distribution.

Results: The mean age was 44 + 10.2 yrs (mean + SD) with 86 females. Gastric bypass surgery was performed in 90% of subjects. The length of Roux limb was 100-150 cm in 77% and > 300 cm in 13% of subjects. The remaining 10% of subjects had either vertical banded gastroplasty or biliopancreatic diversion. Following bariatric surgery, 21 subjects experienced 31 fractures. Mean duration of follow up was 7 years (range 0.04 to 23.2). When compared with fracture incidence rates in SE Minnesota, the SIR for the first fracture at any site was 1.8 (CI 1.1 to 2.8). The SIR for first fracture at hip, wrist, spine and humerus was 1.4 (CI 0.5 to 3.1). The SIR for first fracture at all other sites was 2.1 (CI 1.2 to 3.3) and consisted predominantly of hand 3.3 (CI 1.1 to 7.7) and foot 3.9 (CI 1.9 to 6.9) fractures.

Conclusion: This is a novel study reporting an increased risk of fractures following bariatric surgery. The risk is particularly marked at the hands and feet. Increased bone turnover following bariatric surgery is thus clinically relevant. Further studies need to identify risk factors and understand mechanisms for increased fracture risk in this population.