The striated muscle of the pelvic floor, in common with other striated muscles throughout the body, undergoes a gradual denervation with age . This denervation will result in a gradual weakening of the muscle over time. While some of the aging effect can be counteracted by muscle training, the impact of denervation will be to diminish the number of neurones which can stimulate muscle fibres to contract. Pelvic floor muscle denervation is increased by vaginal delivery, particularly if the active second stage of labour is prolonged .
Caesarean section may offer some protection from this injury. Following childbirth some reinnervation will occur which will result in rehabilitation of the muscle at least to some degree. Reinnervation results in more muscle fibres being innervated by each remaining nerve fibre. This results in the pelvic floor muscle being more vulnerable to age-related denervation since further nerve loss with age will result in a more marked loss of muscle fibre activity. Thus, the damage to the pelvic floor muscle during childbirth often only becomes evident when age-related changes are superimposed. The site of pelvic floor muscle denervation during childbirth is unclear. It has been proposed that stretching of the pudendal nerve distal to Alcock's canal at the ischial spine results in nerve injury but crushing injury at the neuromuscular junction in the muscle must also be possible.
Women with ectopia vesicae have incomplete development of the pelvic floor anteriorly. This predisposes them to uterovaginal prolapse which is an additional surgical challenge to treat partly because of previous surgical procedures and partly because of anatomical distortion from the absence of a normally formed anterior pelvis (bony and soft tissue).
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