The primary objective was to evaluate bone fragility prevalence on dual X-ray absorptiometry (DXA) and computed tomography (CT) in patients with severe obesity. The secondary objective was to evaluate the risk factors for bone fragility. This monocentric study was conducted in patients with grade 2 and 3 obesity. Bone mineral density (BMD) and T-score were studied on DXA, and the scanographic bone attenuation coefficient of L1 (SBAC-L1) was measured on CT. Among the 1386 patients included, 1013 had undergone both DXA and CT within less than 2 years. The mean age was 48.4 (±11.4) years, 77.6% were women, and the mean BMI was 45.6 (±6.7) kg/m². Eight patients (0.8%) had osteoporosis in at least one site. The mean SBAC-L1 was 192.3 (±52.4) HU; 163 patients (16.1%) were under the threshold of 145 HU. Older age (OR[CI95] = 1.1 [1.08–1.16]), lower BMD on the femoral neck and spine (OR[CI95] = 0.04[0.005–0.33] and OR[CI95] = 0.001[0.0001–0.008], respectively), and higher lean mass (OR[CI95] = 1.1 [1.03–1.13]) were significantly associated with an SBAC-L1 ≤ 145 HU in multivariate analysis. Approximately 16% of patients with severe obesity were under the SBAC-L1 threshold, while less than 1% were classified as osteoporotic on DXA.

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BackgroundOsteoporosis is a common disease whose prognosis can be seriously impacted by the development of fractures that lead to functional limitations and may even have life-threatening sequelae (1). CT is useful for diagnosing vertebral fracture (VF) and measuring the scanographic bone attenuation coefficient of the first lumbar vertebra (SBAC- L1). Obesity might be a protective factor against bone loss and osteoporosis (2). Nonetheless, epidemiological studies have reported an association between obesity and an increased risk of fragility fractures (3) and suggested that obesity may be a risk factor for fracture and decreased bone density (4,5). For bariatric surgery, the results are less controversial. According to many studies, malabsorptive procedures lead to a decrease in bone mineral density and sometimes an increased risk of fragility fractures (2,6,7,8). However, the kinetics of bone loss and its physiopathology are unclear.ObjectivesThe primary objective was to evaluate bone fragility on computed tomography (CT) in obese patients before and 2 years after bariatric surgery. The secondary objectives were to identify risk factors for a decrease in the scanographic bone attenuation coefficient of the first lumbar vertebra (SBAC-L1).MethodsThis descriptive study included obese patients who underwent bariatric surgery between January 2014 and December 2019 and CT before and two years (±6 months) after bariatric surgery. SBAC-L1 (in Hounsfield units (HU)) was measured on CT, and vertebral fracture (VF) was manually assessed. The SBAC-L1 fracture threshold was defined as below 145 HU.ResultsAmong the 78 included patients, 85.9% were women, with a mean age of 48.5 years (±11.4); the mean body mass index (BMI) was 46.2 kg/m2 (±7) before surgery and 29.8 kg/m2 (±6.7) 2 years after surgery. There was a significant change in SBAC-L1 two years after surgery (p=0.037). In multivariate analysis, the risk factors for having an SBAC-L1 ≤ 145 HU 2 years after bariatric surgery in those with an SBAC-L1 > 145 HU before surgery were age and sex, with men and older patients having a higher risk (OR = 32.6, CI95% = [1.86-568.77], and OR = 0.85, CI95% = [0.74-0.98], respectively).ConclusionSBAC-L1 was significantly lower two years after bariatric surgery than before surgery. When the SBAC-L1 was over 145 HU before bariatric surgery, men sex and older patients were the risk factors for having an SBAC-L1 below the fracture threshold 2 years after surgery.References[1]Toledano E, Candelas G, Rosales Z, Martínez Prada C, León L, Abásolo L, et al. A meta-analysis of mortality in rheumatic diseases. Reumatol Clin. 2012 Dec;8(6):334–41.[2]Lespessailles E, Paccou J, Javier R-M, Thomas T, Cortet B, GRIO Scientific Committee. Obesity, Bariatric Surgery, and Fractures. J Clin Endocrinol Metab. 2019 Oct 1;104(10):4756–68.[3]Gonnelli S, Caffarelli C, Nuti R. Obesity and fracture risk. Clin Cases Miner Bone Metab. 2014 Jan;11(1):9–14.[4]Greco EA, Fornari R, Rossi F, Santiemma V, Prossomariti G, Annoscia C, et al. Is obesity protective for osteoporosis? Evaluation of bone mineral density in individuals with high body mass index. Int J Clin Pract. 2010 May;64(6):817–20.[5]Compston JE, Flahive J, Hosmer DW, Watts NB, Siris ES, Silverman S, et al. Relationship of weight, height, and body mass index with fracture risk at different sites in postmenopausal women: the Global Longitudinal study of Osteoporosis in Women (GLOW). J Bone Miner Res. 2014 Feb;29(2):487–93.[6]Ko B-J, Myung SK, Cho K-H, Park YG, Kim SG, Kim DH, et al. Relationship Between Bariatric Surgery and Bone Mineral Density: a Meta-analysis. Obes Surg. 2016 Jul;26(7):1414–21.[7]Paccou J, Martignène N, Lespessailles E, Babykina E, Pattou F, Cortet B, et al. Gastric Bypass But Not Sleeve Gastrectomy Increases Risk of Major Osteoporotic Fracture: French Population-Based Cohort Study. J Bone Miner Res. 2020 Aug;35(8):1415–23.[8]Lu C-, Chang Y-K, Chang H-H, Kuo C-S, Huang C-T, Hsu C-C, et al. Fracture Risk After Bariatric Surgery: A 12-Year Nationwide Cohort Study. Medicine (Baltimore). 2015 Dec;94(48):e2087.Disclosure of InterestsNone declared