Biomechanical effects of intra-abdominal pressure and genital hiatus on the pelvic floor in initial injury.

The biomechanical mechanism between genital hiatus (GH), intra-abdominal pressure (IAP) and pelvic organ prolapse (POP) is currently unclear. Therefore, two biomechanical models for comparative analysis are developed to discuss the biomechanical relations of IAP and GH with prolapse of anterior and posterior vaginal walls (AVW and PVW) in the injured pelvic floor system. Based on the magnetic resonance imaging (MRI) of the pelvic floor of a healthy woman, we developed two 2D finite element models by using mechanical equivalence to represent the physiological and pathological states respectively. Both models contain hollow structure rectum. We simulated biomechanical characteristics of POP progression under different IAP and GH values in the PVW injury. In the pathological state with an IAP of 83.9 cmH2O, the descending displacement of the cervix increased from 14.3 to 20.9 mm when the GH increased from 10 to 40 mm. The maximum stress of AVW and perineal body (PB) rose from 0.343 to 0.611 MPa, from 0.190 to 0.974 MPa, respectively. Compared with the physiological state, the initial GH is a significant influence on POP progression. The increase of GH leads to a reduction or loss of biomechanical support for the bladder. The influence of IAPs and GH interaction exacerbates the injury and mechanical imbalance in the pathological state, which triggers increased stress in the AVW and PB, the descending displacements of the cervix and PVM, and exacerbates POP progression.