Anatomy and How Things Go Wrong

There are a large number of anatomic structures within the female pelvis. Pain can come from visceral (intra-abdominopelvic) organs, musculoskeletal structures, and nerves. The internal organs in women include the bladder, bowel or intestines, uterus, ovaries, and the internal genitalia. Musculoskeletal structures include the bony pelvis itself, muscles outside the pelvis in the buttock, pelvic floor or Kegel muscles, pelvic joints (sacroiliac joint and pubic symphysis) and ligaments. In addition, pain referred from the lumbar spine and the hip can cause pelvic pain.

The pelvic organs receive nervous input from the sympathetic (thoracolumbar T10-L2) and parasympathetic (sacral S2-4) systems. The lateral or outside pelvic region transmits pain through parasympathetic nerves arising from S2-S4 whereas the midline structures of the pelvis receive most of their input from sympathetic fibers arising from T10-L1. These fibers coalesce to form the superior hypogastric plexus (SHP or presacral nerve) which lies in the front of the sacral promontory at the L5-S1 level in the low back. The SHP transmits sensory input from the descending and sigmoid colon, rectum, vaginal fundus, bladder, uterus, and ovaries. This plexus then divides into hypogastric nerves that eventually form the inferior hypogastric plexus (IHP). The IHP is the primary coordinating center in the pelvis that integrates both parasympathetic and sympathetic output. Fibers that derive from the IHP innervate the clitoris, vagina, and urethra in women.The pudendal nerve comes from the sacral nerve roots (lowest part of the back) and innervates the front portion of the pelvic floor.

The pelvic floor is composed of layers of muscles connecting the anterior (front) and posterior (back) portions of the pelvic ring and surrounding the urethra, vagina, and anus. Any layer of the pelvic floor musculature can be the pain generator or the source of dysfunction. These muscles facilitate sphincter closure, and support the intra-abdominal organs to prevent pelvic organ prolapse. Their combined optimal function as a neuromuscular unit is integral to maintaining urinary, flatal, and fecal continence. The pelvic floor muscles also contract during orgasm to provide sexual appreciation.  They can be damaged during childbirth, after gynecologic or urologic instrumentation, after repetitive minor trauma from activities such as dance and gymnastics or after incidents of sexual abuse.

The superficial pelvic floor or urogenital diaphragm includes the bulbocavernosus, ischiocavernosus and the transverse perinei. The deep pelvic floor or levator ani includes the puborectalis, pubococcygeus, iliococcygeus and the coccygeus. The piriformis and obturator internus muscles are considered associated muscles and the deep transversus abdominus, lumbar multifidi, and diaphragm are considered synergistic groups. The pelvic floor works dynamically in conjunction with these other muscles to maintain core stability. The pelvic floor is considered the “floor of the core”. Innervation of the pelvic floor in the back or posterior portion is by direct branches from the S2-4 nerve roots, whereas the anterior pelvis is innervated by the pudendal nerve and its three branches, the dorsal nerve to the clitoris, the perineal branch and the inferior hemorroidal nerve.