Urogenital and levator hiatus enlargement is a precursor of pelvic floor dysfunction and conditions such as pelvic organ prolapse.[1] Pregnancy and vaginal birth are known contributors to hiatal enlargement. It is also plausible that enlargement of the urogenital and levator hiatuses may result from unhealthy skeletal muscle aging regardless of parity, although these associations have not been rigorously tested. Skeletal muscle size and strength drive physical performance and, therefore, performance may also be associated with hiatal size. These relationships are important to understand because physical activity is thought to both increase muscle health and physical performance as well as increase hiatal size via repetitive exposure to increased intrabdominal pressure.[2] This study will determine the relationship of hiatus length based on pelvic magnetic resonance (MR) imaging with skeletal muscle measures and physical performance in a cohort of community-dwelling older women. We hypothesized that greater muscle size, strength and physical performance would be associated with smaller urogenital and levator hiatus length among both parous and nulliparous older women.

This cross-sectional analysis included a random sample of 34 parous women and all 54 nulliparous women enrolled in the Study of Muscle Mobility and Aging (SOMMA), a prospective cohort study of adults aged ≥70 years.[3] All available nulliparous women were included to assess aging independently from pregnancy. Eleven women were excluded due to MR-compatible metallic implants, unidentifiable distorted anatomy in the pelvic field of view and inability to visualize anatomy accurately. 

All SOMMA participants completed whole-body MR imaging at baseline. 3D Slicer imaging software (https://www.slicer.org/) was used to measure the urogenital and levator hiatus length. Urogenital hiatus length was measured as the distance between the inferior pubic point (Figure 1, point 1) and perineal body point (Figure 1, point 2). Levator hiatus length was measured from point 1 to the middle of the puborectalis bundle (Figure 1, point 3). Inter-rater reliability for the urogenital (ICC: 0.97 [0.91 0.99], p <.001) and levator (ICC: 0.93 [0.78 0.98], p < .001) hiatus length measures were high.

Seven measures covering domains of physical performance and skeletal muscle health status were included: 1) 400-meter walk time at participants’ usual pace; 2) grip strength assessed using Jamar dynamometers; 3) four square-step test recorded as the fastest time of 3 trials; 4) 1-repetition maximum leg extension strength, and 5) peak leg power measured using the Keiser system; 6) whole body D3-creatine (D3Cr) muscle mass assessed using a D3Cr dilution protocol; and 7) MR thigh muscle volume calculated using fat-free muscle volume from MR images of both thighs.[3] Body mass was measured via scale and used to standardize measures of power and muscle volume. Spearman correlation coefficients stratified by parity status and partial Spearman correlation coefficients adjusted for age plus height were calculated.

Parous and nulliparous women were similar in age (mean = 74.6 vs 75.6 years), but the nulliparous group had higher mean body mass index (27.7 vs 25.7 kg/m2), waist circumference (89.2 vs 83.3 cm), and multimorbidity burden (% with ≥ 1 chronic condition = 89% vs 71%). Parous and nulliparous women reported similar physical activity level, smoking, and history of hysterectomy or lung disease. The overall mean urogenital hiatus length was 50.3 ± 11.2 mm (nulliparous, 50.9 ± 11.5 mm; parous, 49.3 ± 10.5 mm) and mean levator hiatus length was 64.3 ± 7.6mm (nulliparous, 63.8 ± 7.6 mm; parous, 65.2 ± 7.7 mm). When adjusting for age and height, MR thigh muscle volume unadjusted to body mass was significantly correlated to urogenital hiatus length in nulliparous women (r(s) = 0.301, p = 0.03) and levator hiatus length in both nulliparous (r(s) = .291, p = 0.04) and parous women (r(s) = 0.506, p = 0.003); however, when adjusted for body mass, MR thigh muscle volume was no longer significantly correlated with urogenital hiatus or levator hiatus length in either group (Table 1). When adjusted for age and height in parous women only, longer 400-meter walk time was correlated with larger levator hiatus length (r(s) = 0.377, p = 0.03). None of the other measures of muscle size, strength or physical performance were significantly associated with urogenital or levator hiatus length in nulliparous or parous women (Table 1).

Except for 400-meter walk time, muscle size, strength and performance were not correlated with hiatal length, regardless of parity status. In parous women only, longer 400-meter walk time was associated with a greater levator hiatus length, possibly indicating a greater risk of pelvic organ prolapse. Hiatal length measures obtained were congruent with those reported in the literature.

Measures of muscle size, strength and physical performance were not associated with urogenital or levator hiatal length in community-dwelling older women regardless of parity status. This is important because increased hiatal size is a known precursor of pelvic organ prolapse development and physical activity, a major determinant of skeletal muscle health and physical performance, is thought to increase hiatal size. Conversely, in parous women, worse physical performance measured by longer 400-meter walk time was associated with greater hiatal length.

Cheng W, English E, Horner W, et al. Hiatal failure: effects of pregnancy, delivery, and pelvic floor disorders on level III factors. Int Urogynecol J. 2023;34(2):327-343. doi:10.1007/s00192-022-05354-8
Bø K, Nygaard IE. Is Physical Activity Good or Bad for the Female Pelvic Floor? A Narrative Review. Sports Medicine. 2020;214(2):471-484. doi:10.1007/s40279-019-01243-1
Cummings SR, Newman AB, Coen PM, et al. The Study of Muscle, Mobility and Aging (SOMMA): A Unique Cohort Study About the Cellular Biology of Aging and Age-related Loss of Mobility. J Gerontol A Biol Sci Med Sci. 2023;78(11):2083-2093. doi:10.1093/gerona/glad052

Continence 12S (2024) 101628
DOI: 10.1016/j.cont.2024.101628