Urinary incontinence (UI), osteoporosis, and falls are highly prevalent conditions among older women. The current study aims to compare bone mass, bone quality, and muscle strength (hip and pelvic floor muscles) in postmenopausal women with UI versus no UI. We hypothesized that women with UI have lower skeletal muscle strength compared to those without UI.

For this cross-sectional study, women 55 years or older undergoing universal osteoporosis screening were recruited from 6/2018 to 6/2020. The presence of UI was defined as having 1) at least moderate UI (scores ≥3 on a validated UI severity index [1]), 2) positive cough stress test, or 3) history of UI treatments. Bone mass and quality were assessed by bone mineral density (BMD) and trabecular bone score (TBS), respectively, via Dual-Energy X-ray Absorptiometry (DXA). Low bone mass (osteopenia or osteoporosis) was defined using the traditional World Health Organization criteria [2], a T-score <-1, low bone quality as TBS ≤1.31. Maximum hip muscle strength (peak isometric muscle contraction, pounds-force) was assessed using a hand-held dynamometer, and pelvic floor muscle strength (peak squeeze pressure, cmH2O) by a perineometer, respectively. The mean of 3 measurements were analyzed. Student’s t-test was used for continuous variables, and Chi-square test, Fisher’s exact test, or Cochran–Mantel–Haenszel test were used for categorical variables as appropriate. Hip muscle strength was compared between groups using generalized linear models adjusting for covariates potentially influencing the difference observed between groups. Statistical significance was indicated at a 0.05 level.

Of 41 women, 18 had UI, 23 had no UI. No differences in clinico-demographic characteristics were noted between groups; age (UI 67.9 ± 5.5 versus no UI 66.0 ± 4.5, p=0.24), White race (67% versus 44%, p=0.14), BMI (30.6 ± 9.2 versus 30.8 ± 6.2, p=0.94), as well as comorbidities (chronic lung disease, cardiovascular, stroke, diabetes mellitus, arthritis, depression), estrogen use, vaginal delivery, hysterectomy, or smoking status (Table 1). Bone assessment did not differ between groups; low bone mass by BMD (osteopenia or osteoporosis, UI 50% versus no UI 40%, p=0.37), low bone quality by TBS (UI 56% versus no UI 30%, p=0.11).There was no significant difference in pelvic floor muscle strength (UI 32.1 ± 18.6 cmH2O, no UI 37.6 ± 22.4 cmH2O, p=0.25). However, women with UI had significantly lower hip muscle strength in hip flexion, abduction, adduction, external and internal rotation, compared to those with no UI controlling for age and race (Table 2), and additionally controlling for bone mass and quality (Table 2).

While no significant difference was detected in pelvic floor muscle strength between groups, women with UI had lower hip muscle strength as measured by peak isometric muscle contraction, compared to those without UI.

The continence mechanism relies on intact pelvic floor support consisting of pelvic floor muscles and connective tissue which are anchored to the bony pelvis. Thus, surrounding anatomic structures beyond the pelvic floor could play an important role in maintaining pelvic floor strength and function responsible for continence through muscle co-activation. Therefore, targeting an increase in hip muscle strength with pelvic floor muscle strength may improve pelvic floor function. A combination of hip and pelvic floor interventions may be warranted in older women with UI.

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