One in five postmenopausal women was eligible for AOM (22.5%, n = 69/306) based on the ECTS position statement as part of their care pathway, either before or after MBS. This prevalence was significantly higher in women aged ≥ 60 years than in those aged < 60 years (30.1% vs. 16.8%, p = 0.006). Beyond the age of ≥ 60 years, factors such as active smoking, secondary hyperparathyroidism, and decreased ALMI were identified as independent risk factors.

Of the 306 postmenopausal women who underwent a bariatric surgery care pathway, 69 were assessed prior to their first surgery, 191 during follow-up, and 46 prior to a subsequent surgery. According to the 2022 ECTS criteria, 22.5% of the 306 postmenopausal women in our cohort were eligible for AOM, consistent with Courtalin et al., who reported a 19.2% prevalence among 170 men over 50 and postmenopausal women, with no difference by surgical status [11]. Few studies have simultaneously assessed fractures and BMD after bariatric surgery. Blom-Høgestøl et al. followed 194 patients, including 59 postmenopausal women or men over 50, for 10 years after RYGB, finding osteopenia in 51%, osteoporosis in 27%, and 19% experiencing a low-energy fracture [12]. In comparison, almost 10% of our patients had sustained a fragility fracture within the preceding two years. However, Blom-Høgestøl et al. did not report the proportion of patients with a T-score ≤ –2, limiting direct comparison. Other studies focused on BMD loss: Lindeman et al. followed 21 patients up to five years after RYGB, observing significant decreases at the lumbar spine (−7.8%) and total hip (−15.3%) [13]. Schäfer et al. analyzed postmenopausal women separately and found greater preoperative vulnerability and more pronounced BMD loss at 12 months (total hip –12.2%) compared to premenopausal women (−7.2%) and men (−6.8%, p ≤ 0.02) [14]. Collectively, these findings confirm the heightened skeletal risk in postmenopausal women following MBS, although direct comparisons remain limited due to inconsistent reporting of T-scores ≤ -2.

While postoperative complications of MBS in patients over 60 have been well documented, few studies have specifically addressed bone health. The French HAS highlighted increased morbidity and mortality in older adults [3] but did not provide guidance on musculoskeletal assessment or fracture risk screening. An American study of 351,292 patients (12.6% aged > 65) reported a 3% postoperative mortality rate and higher rates of infectious, respiratory, and hospital-related complications among older adults [15]. Another study comparing RYGB and SG in patients ≥ 65 found frequent RYGB complications, including gastrointestinal ulcers (7.2%), anastomotic strictures (5.9%), and reinterventions (4.7%) [16]. However, no study has specifically examined bone-related consequences in this vulnerable group. Osteoporosis significantly contributes to morbidity and mortality, with one-year post-hip fracture mortality in older adults estimated at 15–30% [17], underscoring the need to evaluate long-term musculoskeletal outcomes in older postmenopausal women.

Beyond age, we aimed to identify risk factors, particularly modifiable ones, independently associated with eligibility for AOM, with the goal of targeting preventive strategies and better identifying high-risk populations.

Elevated iPTH emerged as an independent predictor of AOM eligibility, consistent with its role in bone resorption and skeletal fragility in secondary hyperparathyroidism [18, 19]. Supporting this, Wei et al. reported an increase in secondary hyperparathyroidism from 21% preoperatively to 35% one year after bariatric surgery (SG, RYGB, AG), primarily driven by vitamin D deficiency [20], a finding echoed in Saudi patients undergoing SG [21]. In our cohort, over 25% of patients had iPTH > 66 pg/mL, reflecting suboptimal vitamin D status (mean 25(OH)D: 25.8 ng/mL) and insufficient supplementation. French guidelines recommend maintaining 25(OH)D levels between 30–60 ng/mL, with monthly supplementation of 100,000 IU after RYGB and 50,000 IU after SG [22], highlighting a persistent gap between recommendations and real-world practice that underscores the need to optimize preventive strategies. Calcium absorption is compromised following both RYGB and SG. Consequently, even under conditions of optimal vitamin D status, PwO may not achieve adequate calcium absorption after bariatric surgery, which could constitute an additional mechanism underlying elevated iPTH levels.

Muscle parameters also significantly influence therapeutic decisions. Reduced ALMI (≤ 5.5 vs. > 5.5 kg/m2) was identified as an independent risk factor for initiating AOM, likely reflecting the loss of muscle’s mechanical and metabolic support for bone, which disrupts remodeling and decreases BMD [23]. Sarcopenia, particularly sarcopenic obesity, combines reduced muscle mass and strength with excess adiposity, impairing bone quality, increasing fall risk, and raising fracture incidence [24]. In postmenopausal women, lower appendicular muscle mass correlates with BMD loss at vulnerable sites such as the femoral neck, further elevating osteoporosis risk [25]. Tailored physical activity programs following MBS have been shown to mitigate postoperative bone loss, particularly in patients at risk of sarcopenic obesity [26, 27].

Physical inactivity is common among candidates for MBS, with fewer than 30% meeting the WHO-recommended 150 min of moderate weekly activity [28, 29]. Sedentary behavior, averaging over eight hours of sitting per day, exacerbates the metabolic and musculoskeletal consequences of severe obesity [30]. French guidelines stress that adequate protein intake, often insufficient in this population, is essential to preserve muscle mass and should complement regular physical activity [22].

Active smoking also emerged as a strong determinant of AOM eligibility, conferring a three-fold increased risk. This finding reinforces the well-established role of tobacco in accelerating bone loss and osteoporosis [31, 32], and is consistent with Fashandi et al., who identified smoking as an independent predictor of fractures after MBS [33]. Collectively, these observations highlight the critical need to systematically integrate lifestyle interventions—including smoking cessation, structured physical activity, and adequate protein and calcium/vitamin D supplementation—into the pre- and postoperative management of postmenopausal women.

This study has several strengths. It was based on prospective inclusion with standardized and comprehensive data collection, including DXA scans, biochemical markers, MBS history, and clinical risk factors for osteoporosis. The sample size (n = 306) provided adequate power to identify factors associated with AOM eligibility. Over 95% of DXA scans were performed on the same device at Lille University Hospital, ensuring measurement consistency. Biochemical data, particularly vitamin D and iPTH levels, were available for over 90% of patients. Importantly, this is the first study to specifically investigate musculoskeletal health and independent risk factors for AOM eligibility in postmenopausal women aged ≥ 60 years undergoing bariatric surgery.

This study also has limitations. Its retrospective analysis may have introduced recall bias and missing data, particularly regarding fracture history or specific risk factors. Not all biochemical markers were systematically or recently assessed, potentially limiting interpretation, although overall data completeness remained high. Alcohol and smoking were self-reported, which may have led to underestimation. The cohort was heterogeneous, including both pre- and post-operative patients at various stages, reflecting real-world practice but introducing variability. Referral bias may have led to overrepresentation of postmenopausal bariatric women at higher fracture risk, potentially overestimating the prevalence of AOM eligibility. Finally, the monocentric design and the high proportion of previously operated patients (> 75%) may limit generalizability to other settings. Another limitation is the lack of a non-bariatric control group, limiting assessment of whether prevalence deviates from age-adjusted expectations.

Our findings emphasize the crucial importance of preventing and managing secondary osteoporosis both before and after MBS in postmenopausal women, particularly those aged 60 years and older. Beyond age, several independent risk factors were identified, underscoring the essential role of lifestyle interventions alongside AOM. Specifically, smoking cessation, minimizing sedentary behavior, and ensuring lifelong vitamin D and calcium supplementation to prevent secondary hyperparathyroidism should remain central priorities in both preoperative and postoperative care.