Bone Structural Changes and Estimated Strength After Gastric Bypass Surgery Evaluated by HR-pQCT

Abstract

Roux-en-Y gastric bypass surgery (RYGB) is an effective treatment of morbid obesity, with positive effects on obesity-related complications. The treatment is associated with bone loss, which in turn might increase fracture risk. The aim of this study was to evaluate changes in bone mineral density (BMD) and bone architecture assessed using dual-energy X-ray absorptiometry (DXA) and high-resolution peripheral quantitative computed tomography (HR-pQCT), 6 and 12 months after RYGB, and correlate them to changes in selected biochemical markers. A prospective cohort study included 25 morbidly obese patients (10 males, 15 females). Patients were examined with DXA of the hip and spine, HR-pQCT of radius and tibia, and blood sampling before and 6 and 12 months after RYGB. Patients lost in average 33.5 ± 12.1 kg (25.8 ± 8.5 %) in 12 months. In tibia, we found significant loss of total, cortical and trabecular volumetric BMD after 12 months (all p < 0.001). Microarchitectural changes involved lower trabecular number, increased trabecular separation, and network inhomogeneity along with thinning of the cortex. Estimated bone failure load was decreased after 12 months (p = 0.005). We found only minor changes in radius. Results demonstrate significant alterations of bone microarchitecture suggesting an accelerated endosteal resorption along with disintegration of the trabecular structure which resulted in a loss of estimated bone strength in tibia. Such changes may underlie the recently reported increased risk of fracture in bariatric patients after surgery. We only observed bone structural changes in the weight-bearing bone, which indicates that mechanical un-loading is the primary mediator.

Bone turnover after bariatric surgery

“…Moreover, urinary DPYD was also higher in BS patients than in Cont, indicating an increased bone resorption, as detected by other investigators (20,21), even when using different bone resorption markers as well (8,20,22,23). Therefore, an increased bone turnover has been clearly evidenced by the present findings, which corroborates with numerous reports (8,12,13,15,24), although not with all of them (9,21).…”

“…When compared to Cont, bariatric patients from the current series presented a lower mean value of serum leptin, one of the most important cytokines derived from fat tissue, which acts on hypothalamic neurons by stimulating sympathetic postganglionic neurons via axons that enter the bones to inhibit bone formation (31,32). Our findings are in agreement with other reports after bariatric surgery (13,15). Bruno and cols.…”

“…Of note, we found a positive correlation of serum BAP with time after surgery. A substantial increase in bone formation and resorption markers had occurred up to 24 months after gastric bypass despite weight stability, as described by many authors (12,13,29), reinforcing that bone remodeling remains elevated despite weight loss plateaus after the first year and are not exclusively due to mechanical unloading of the skeleton.…”

“…In the current series, despite of the low calcium consumption besides hypovitaminosis D, BS group did not present a higher median serum PTH. Nevertheless, the presence of secondary hyperparathyroidism among bariatric patients is still a matter of debate since some investigators reported normal levels of PTH (8,13,15), while others did not (14,18,19).…”

“…Previous studies that evaluated skeletal changes after bariatric surgery through dual-energy x-ray absorptiometry (DXA), quantitative computed tomography (QCT) and high-resolution peripheral computed tomography (HR-pQCT) demonstrated a decreased BMD and also increased bone turnover markers (7,9,(12)(13)(14)(15).…”