UroToday.com - During vaginal delivery of children, both the muscles and the nerves are compressed and injured.1,2 This includes the external urethral sphincter (EUS), the striated muscle of the urethra, and the pudendal nerve which innervates the EUS (Figure 1). Three months postpartum, 34.3% of women have some degree of urinary incontinence (SUI).3 Insufficient recovery from these two injuries, along with other pelvic floor injuries are strongly correlated with later development of SUI.4

Based on pathophysiological theories of urethral sphincter dysfunction, several animal injury models for SUI designed to simulate maternal birth trauma, have been established in the past few years.5 These include the SUI dual injury model that we developed that involves both pudendal nerve crush (PNC) and vaginal distension (VD).6,7 The dual injury model perhaps best represents the injuries incurred due to vaginal delivery since it involves injuries to muscles, nerves, and supporting tissues.

We have demonstrated delayed recovery of urethral function after a dual simulated childbirth injury using simultaneous measurements of urethral resistance and electrophysiological recordings, including leak point pressure (LPP), EUS electromyography (EMG), and pudendal nerve motor branch potentials (PNMBP).6,8 We have also shown that neurotrophin expression in the EUS is upregulated after PNC but is downregulated after either VD alone or after a dual injury of PNC+VD…