Urinary incontinence (UI) and osteoporosis share common risk factors including advanced age. Continence is maintained by intact pelvic support consisting of pelvic floor muscles and connective tissue (most abundantly collagen) which are attached to the bony pelvis. Abnormal collagen metabolism could lead to poor pelvic floor support and function resulting in UI. Skeletal integrity depends on the quantity and quality of connective tissue influenced by extracellular matrix predominantly collagen, similar to pelvic floor support. Thus, there may be a pathophysiologic association between UI and skeletal fragility as global alteration of the collagen metabolism. Existing data suggesting the potential association between skeletal fragility and pelvic floor disorders including UI are limited and are solely based on bone mineral density (BMD), which only measures bone quantity. Our primary aim was to characterize the association between UI and skeletal fragility defined by a combination of quantity and quality bone assessment in postmenopausal women undergoing osteoporosis evaluation. We further examined the impact of bone quantity and bone quality on pelvic floor symptoms separately, as well as the association with fecal incontinence (FI) and pelvic organ prolapse (POP).

Postmenopausal women undergoing an osteoporosis evaluation from 2007 to 2010 were identified from an institutional review board approved osteoporosis database which included baseline demographic data and validated pelvic floor symptom questionnaires. The presence of UI (any UI) was defined as leakage of urine at least 2-3 times per week in the past 3 months. The types of UI, stress (SUI) urgency (UUI), or mixed UI (MUI) were defined using the 3 incontinence Questions (3IQ). FI was defined as liquid or solid stool leakage at least once a month using the Fecal Incontinence Severity Index (FISI), and POP as a positive response to “Do you have a bulge or something falling out that you can see or feel in your vaginal area?” from the Pelvic Floor Distress Inventory-20 (PFDI-20). Bone quantity and quality were assessed using BMD and trabecular bone score (TBS), respectively. Skeletal fragility was defined as follows; i) a combined BMD and TBS index equivalent to moderate/severe fracture risk;[1,2] ii) low bone quality, TBS≤1.31;[2] iii) low bone quantity using the traditional World Health Organization criteria, a T-score < -1 or currently on BMD medication.[3] Student’s t-test was used for continuous variables, whereas Chi-square test, Fisher’s exact test, or Cochran–Mantel–Haenszel test were used for categorical variables as appropriate. Multivariate logistic regression was performed to further assess the association between skeletal fragility and pelvic floor symptoms adjusting for covariates potentially influencing the difference observed between groups. Statistical significance was indicated at a 0.05 level.

Of 681 subjects, 262 and 419 were classified as skeletal fragility versus (vs.) normal using the combined (TBS and BMD) bone assessment. Demographic characteristics were similar between groups except for age (69.0 ± 8.2 vs. 65.0 ± 7.1, p<.001) and smoking (8.8% vs. 3.3%, p<.001). On bivariate analyses, women meeting the combined skeletal fragility criteria had a higher rate of any UI (49.4% vs. 41.4%, p=0.042) and SUI (37.5% vs. 30.1%. p=0.047, Table 1). Using the combined bone assessment, multivariable regression revealed women with skeletal fragility had an increased odds of having any UI (aOR 1.48, 95%CI: 1.05-2.10), SUI (aOR 1.53, 95%CI:1.06-2.21), and MUI (aOR 1.45, 95%CI:1.02-2.05, Table 2). Using the TBS only criteria, women with low bone quality had a higher rate of any UI, SUI, UUI, and MUI (p<0.05, Table 1). Upon multivariable regression, low bone quality was independently associated with an increased risk for any UI (aOR 1.68, 95%CI: 1.15-2.41), SUI (aOR 1.61, 95%CI:1.10-2.36), UUI (aOR 1.65, 95%CI:1.13-2.41), and MUI (aOR 1.64, 95%CI:1.14-2.38, Table 2). Using the BMD only criteria, no difference in UI, FI, or POP was observed between groups (p>0.05, Table 1) or on multivariate analyses (Table 2).

Postmenopausal women with skeletal fragility using the combination assessment (TBS and BMD) as well as those with low bone quality (TBS) are associated with an increased risk of UI but not FI or POP. Osteoporosis using the traditional definition (low bone quantity, BMD) was not associated with an increased risk of pelvic floor symptoms in postmenopausal women.

A potential association between pelvic floor disorders and osteoporosis has been previously reported, however existing data are based solely on BMD. The current study utilized the novel skeletal integrity assessment with the traditional bone density (BMD) and bone quality index (TBS). Using the comprehensive bone assessment, skeletal fragility and poor microarchitecture were independently associated with UI. A pathophysiologic link may exist between skeletal fragility and UI sharing a common underlying mechanism.

Hans D, Goertzen AL, Krieg MA, et al. Bone microarchitecture assessed by TBS predicts osteoporotic fractures independent of bone density: the Manitoba study. JBoneMinerRes.2011;26(11):2762–9.
Hans D, Stenova E, Lamy O. The Trabecular Bone Score (TBS) Complements DXA and the FRAX as a Fracture Risk Assessment Tool in Routine Clinical Practice. Curr Osteoporos Rep 2017; 15:521–531
Kanis JA, Melton LJ III, Christiansen C, et al. The diagnosis of osteoporosis. J Bone Miner Res. 1994; 9:1137–1141