Anatomical basis for contribution of hip joint motion by the obturator internus to defaecation/urinary functions by the levator ani via the obturator fascia

Abstract

The functional association between hip joint motion and defaecation/urinary function has attracted considerable research and clinical attention owing to the potential novel approaches for pelvic floor rehabilitation; however, the anatomical basis remains unclear. This study, therefore, aimed to analyse the anatomical basis of force transmission between the obturator internus, a muscle of the hip joint, and the levator ani, a muscle of the pelvic floor. Twenty‐three cadavers were used for macroscopic and histological analyses. The three‐dimensional structures of the muscles and fascia were recorded using a high‐definition camera and a 3D scanner. The arrangement and attachment of the muscle fibres, tendons and fascia were visualised using histological sections stained with Masson's trichrome. The obturator internus and levator ani were in broad contact through the obturator fascia. The height of their contact area was 24.6 ± 9.1 mm. Histologically, the obturator internus and levator ani shared a large area of the obturator fascia, and the obturator fascia provided the attachment of several muscle layers of the levator ani. The contribution of hip joint motion to defaecation/urinary function can be explained by the broad ‘planar’ contact between the obturator internus and levator ani. This anatomical feature suggests that movement of the obturator internus creates the foundation for the function of the levator ani and contributes to pelvic floor support through the obturator fascia. This study provides an anatomical basis for the effectiveness of the hip muscles in improving defaecation/urinary function by enabling balanced and proper movements.

Twisted orientation of the muscle bundles in the levator ani functional parts in women: Implications for pelvic floor support mechanism

“…Recent studies have shown that the area in which the LA originates from the obturator fascia is broader than previously thought (Muro et al, 2023). However, it remains unclear which parts of the LA originate from the pubis and TALA, as well as the corresponding origin and insertion points.…”

“…During layer‐by‐layer dissection, the pelvic halves specimens were dissected from the medial aspect. This approach has been employed in our previous studies and allows for the sequential demonstration of layered structures while maintaining the spatial positioning of the rectum and pelvic muscles (Muro et al., 2014 , 2018 , 2019 , 2020 , 2023 ). In the present investigation, following the observation of the structures in the median section, the LA and coccygeus were dissected while preserving the rectum, and the attachment site of the LA to the rectum was examined.…”

“…To visualise the spatial positional relationship between muscle bundles, each step of the layer‐by‐layer dissection process involved in the sequential removal of structures according to their stratigraphy was scanned in 3D (EinScan‐SE; Japan 3D Printer Co., Ltd) (Muro et al., 2023 ). The acquired 3D data were aligned and processed using Autodesk Meshmixer version 3.1 (Autodesk; https://www.meshmixer.com/ ).…”

Significant relationship between musculoaponeurotic attachment of the abdominal and thigh adductor muscles to the pubis: implications for the diagnosis of groin pain

“…To obtain the blocks, the superior and inferior borders were made at approximately 1 cm superior and inferior to the pubic symphysis, whereas the medial and lateral borders were made at the mid-sagittal line and at approximately 6 cm lateral to the midline, respectively. The tissue blocks were decalcified in Plank-Rychlo solution (AlCl 3 :6H 2 O, 126.7 g/L; HCl, 85.0 mL/L; HCOOH, 50.0 mL/L) (Fukai et al 2022 ; Muro et al 2023 ; Norose et al 2022 ; Plank and Rychlo 1952 ) for 4 weeks. A graded ethanol series was used for the dehydration process.…”

Pelvic floor and perineal muscles: a dynamic coordination between skeletal and smooth muscles on pelvic floor stabilization

“…A recent topic of interest regarding LA is its relationship to the obturator internus, a muscle of the hip joint. The LA was found to be in broad planar contact with the obturator internus and has several muscle layers attached to the obturator fascia (Muro et al 2022 ). Based on these anatomical findings, we assume a functional relationship in which the dynamic movement of the obturator internus cooperates with the LA through the obturator fascia, providing the foundation for the function of the LA.…”