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Sleeve gastrectomy reduced vertebral bone strength and density of adolescents

Sleeve gastrectomy has been found to have harmful effects on bones of adolescents and young adults by reduced vertebral bone strength and density and increased bone marrow adipose tissue (BMAT) - a marker of bone weakening - compared with non-surgical control participants, according to a by researchers at Harvard Medical School in Boston, MA.

Figure 1: Biomechanical noncontrast CT analysis of the L1 vertebra in an 18-year-old woman with severe obesity (body mass index [BMI], 48.4 kg/m2) prior to sleeve gastrectomy (SG) and 24 months after surgery (BMI, 26.6 kg/m2). L1 vertebra was loaded to 9820 N at both visits for comparison purposes. Breaking strength was (A) 11 920 N at baseline prior to SG and (B) 9820 N at 24 months after surgery. Cutout views of the finite element models under compressive load depict the distribution of bone mineral density (black and white areas) and bone failure (coloured areas). Red indicates tissue that failed earlier during the compressive load (weaker bone). Shades of grey indicate different bone densities, with white being dense bone and black being little or no bone mineral (Credit: Radiological Society of North America).

"Childhood obesity is on the rise and weight-loss surgery is the most effective way to reduce weight and improve cardiometabolic comorbidities," said the study's lead investigator, Dr Miriam A Bredella, professor of radiology at Harvard Medical School and vice chair for Faculty Affairs and Clinical Operations, Department of Radiology Massachusetts General Hospital in Boston. "This is the first study in adolescents and young adults that examined the long-term effects of sleeve gastrectomy, the most common type of weight-loss surgery, on bone strength and bone marrow fat."

The aim of the study was to determine the long-term effects of sleeve gastrectomy on vertebral bone strength, density and BMAT in adolescents and young adults (age of 13 and 24 years) with moderate to severe obesity. In total, there were 54 participants, 25 who underwent sleeve gastrectomy (mean age, 18 years ± 2 [SD], 20 female), and 29 (mean age, 18 years ± 3, 21 female) who were in the control group. Forty-one study participants were female. The surgical group included participants with at least one obesity-related co-morbidity or a BMI at or above 40. The control group had obesity but did not plan to undergo sleeve gastrectomy but received dietary and exercise counselling.

The two-year prospective non-randomised longitudinal study enrolled adolescents and young adults at an academic medical centre from 2015 to 2020. Participants underwent quantitative CT of the lumbar spine (L1 and L2 levels) to assess bone density and strength, proton MR spectroscopy to assess BMAT (L1 and L2 levels), and MRI of the abdomen and thigh to assess body composition. Student t and Wilcoxon signed-rank tests were used to compare 24-month changes between and within groups. Regression analysis was performed to evaluate associations between body composition, vertebral bone density, strength, and BMAT.

Before and 24 months after sleeve gastrectomy, participants underwent a physical examination, blood tests and quantitative CT of the lumbar spine, to quantify volumetric bone mineral density and to perform finite element analysis, a technique that can estimate bone strength. Quantitative CT is a highly accurate technique for detecting changes in volumetric bone mineral density after extreme weight loss. Studies have shown that bone marrow fat responds to changes in nutrition and may serve as a biomarker for bone quality. Therefore, patients underwent proton MR spectroscopy to quantify bone marrow fat of the lumbar spine.

Two years following surgery, BMI in the adolescents and young adults dropped (-11.9, on average p<0.001), while there was a slight rise in BMI in the control group (+1.5, on average, p=0.02). Mean bone strength of the lumbar spine decreased after surgery compared with that in control subjects (mean decrease, −728 N ± 691 vs −7.24 N ± 775; p<0.001). BMAT of the lumbar spine increased after SG (mean lipid-to-water ratio increase, 0.10 ± 0.13; p=.001). Changes in vertebral density and strength correlated positively with changes in BMI and body composition (R = 0.34 to R = 0.65, p=0.02 to p<0.001) and inversely with vertebral BMAT (R = −0.33 to R = −0.47, p=0.03 to p=0.001).

"We found that bone strength was lower two years after weight-loss surgery, while bone marrow fat, a marker of bone weakening, was increased, suggesting that weight-loss surgery has negative effects on bone health," added Bredella. "As bariatric surgery is increasingly performed in adolescents, its effect on bone health needs to be emphasised, especially to the physicians who will continue to provide routine medical care for these patients. We hope that our study will raise awareness on the effects of weight-loss surgery on bones in adolescents with obesity."

She noted that the adolescent years are a critical time for building up bone mass, and deficits in bone accrual during these years could have a long-term impact on bone health and fracture risk in this younger population later in life. Raising awareness of the importance of bone health will allow for monitoring and management of low bone mass, optimal dietary supplementation with vitamin D and calcium, and the initiation of appropriate therapy, if necessary.

"Our observed effects of weight-loss surgery on bone strength and bone marrow fat might also identify new targets for novel therapies," she concluded.

The paper, ‘Two-year Skeletal Effects of Sleeve Gastrectomy in Adolescents with Obesity Assessed with Quantitative CT and MR Spectroscopy’, was published in Radiology.


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