OR13-04 Risk Of Wrist Fracture In Gastric Bypass Compared To Gastric Banding As Estimated By The Load-To-Strength Ratio

Disclosure: G.H. Jung: None. B. Zahedi: None. K. Lindeman: None. C.C. Rushin: None. M.C. Cheney: None. M.L. Bouxsein: None. E.W. Yu: Grant Recipient; Self; Amgen Inc. Background: Bariatric surgeries such as Roux-en-Y gastric bypass (RYGB) and adjustable gastric banding (AGB) lead to long-term deficits in bone density but are also accompanied by decreased weight, which may lower the impact force with falls. Given that risk of fracture is dependent on both bone strength and the external force applied to bone, the clinical implications of these opposing effects are unclear. The aim of this study is to compare the long-term skeletal impact of RYGB and AGB using a biomechanical evaluation of load-to-strength ratio as a surrogate for fracture risk. Methods: We examined a cohort of adults who received RYGB and AGB surgery ≥ 10 years ago (RYGB: n=25; AGB: n=25). We computed the load-to-strength ratio at the distal radius as a ratio of impact force to bone strength, with higher load-to-strength ratios representing a higher susceptibility to fracture. Impact force (F) was calculated for a forward fall via a single-spring biomechanical model. High-resolution peripheral quantitative CT was used to estimate bone strength via microfinite element analysis. Participants also had dual-energy X-ray absorptiometry measurements of areal bone mineral density (aBMD) at the spine, hip, and distal radius, along with laboratory evaluations (parathyroid hormone, PTH; C-telopeptide, CTX; type 1 procollagen, P1NP; 25OH-vitamin D). Differences in bone outcomes between RYGB and AGB groups were compared using generalized linear modeling in R version 4.2.2 and adjusted for age, sex/menopausal status, and race/ethnicity. Results: The RYGB and AGB groups were each comprised of 22 women and 3 men. Compared to AGB, the RYGB group was younger (56 vs 62 years), had more premenopausal women (41% vs 9%), more individuals who identified as Black (36% vs 8%) and longer duration since surgery (13 vs 11 years) (p<0.05 for all). Current BMI (34.5 kg/m^2) was similar between groups, although postsurgical weight loss was higher in RYGB (45 vs. 27 kg, p<0.001). In multivariate analysis, in comparison to AGB, the RYGB group had 98% higher CTX and 34% higher P1NP levels (P<0.01 for both), as well as 20% lower total vBMD at the distal radius, 12% lower total hip, 10% lower femoral neck and 8% lower spinal aBMD (P<0.05 for all). Although impact forces were similar in the 2 groups, RYGB had a 12% lower estimated bone strength (3768 ± 182 vs. 4236 ± 193 N, p=0.01). Load-to-strength ratio was numerically higher in RYGB as compared with AGB (0.78 ± 0.05 vs 0.69± 0.06, p=0.1), suggestive of higher fracture risk, although this did not reach statistical significance. Conclusions: Despite achieving similar postoperative weight as AGB, RYGB patients had lower estimated bone strength at the distal radius, higher bone turnover markers, lower BMD and a trend for higher load-to-strength ratio ≥10 years after surgery. Taken together, these results indicate the long-term deleterious skeletal effects are more concerning with RYGB than AGB. Presentation: Friday, June 16, 2023