4-2 Genital Anatomic Correlates Kevin J. Stepp and Matthew D. Barber The Cleveland Clinic Foundation uses a multidisciplinary surgeon. The anterior superior iliac spine is located ante- approach to the patient with pelvic floor dysfunction. What rior and laterally on the superior ileum. This is easily follows is intended to be a clinical resource for surgical identifiable in all patients and is a clinically useful land- anatomy for the pelvic surgeon. This section will cover the mark. The ischium is fused to the ilium. The medial surface anatomic relationships of the bones, ligaments, viscera of of the ilium has two concavities forming the lateral borders the pelvis, and their supportive structures as they relate to the of the pelvic outlet. The superior and larger of the two is female reproductive tract.A detailed discussion of the urinary the greater sciatic notch. Inferiorly is the lesser sciatic tract and colorectal anatomy is provided elsewhere. A thor- notch. They are separated by a projection medially, called ough mastery of the anatomic concepts presented here will the ischial spine. The ischial spine is important clinically serve as a foundation for clinical examination and surgical and anatomically because it can be palpated easily through repair of pelvic floor dysfunction and pelvic organ prolapse. a vaginal, rectal, or retropubic approach, and many sup- portive structures attach to it. The ischial spine is useful as a fixed point to describe the relative position of other Bones of the Pelvis anatomic structures. The superior and inferior pubic rami are located anteri- The bones of the pelvis are the rigid foundation to which orly and articulate in the midline at the pubic symphysis. all of the pelvic structures are ultimately anchored. It is The ridge along the superior, medial surface of the important to understand and discuss the bony pelvis from superior pubic rami is called the pectineal line, or Cooper’s the perspective of a standing woman. In the standing posi- ligament. tion, forces are dispersed to minimize the pressures on the In the standing position, the anterior superior iliac spine pelvic viscera and musculature and disperse the forces to and pubic symphysis are in the same vertical plane (Figure the bones that are better suited to the long-term, cumula- 4-2.2). This directs the pressure of the intraabdominal and tive stress of daily life. In the upright position, the pubic pelvic contents toward the bones of the pelvis instead of the rami are oriented in an almost vertical plane. Similar to the muscles and endopelvic fascia attachments of the pelvic supports of an archway or bridge, the weight of the woman floor.The posterior surface of the pubis symphysis is located is transmitted along these bony supports to her femurs. in a plane approximately 2 to 3cm inferior to the ischial Where the pubic rami articulate in the midline, they are spine.Therefore,a line drawn connecting the two structures nearly horizontal.Much of the weight of the abdominal and would be almost horizontal in the standing position. pelvic viscera is supported by the bony articulation inferi- Strong ligaments hold the bones together. The ligaments orly. In this way, increases in intraabdominal pressures are of the sacroiliac joint are rarely encountered during partially supported by the bony pelvis. surgery for pelvic floor dysfunction and are not addressed The pelvic bones are the ilium, ischium, pubic rami, here. The sacrospinous ligament is a strong, easily sacrum, and coccyx (Figure 4-2.1). The sacrum is com- identifiable ligament that extends from the ischial spine to posed of five sacral vertebrae that are fused together. The the distal sacrum. The ligament fans out to attach on the nerve foramina are positioned anterior and laterally. Over- S1-S4 vertebrae. This ligament divides the lateral pelvic lying the middle of the sacrum is a rich neurovascular bed. outlet into two foramina, the greater sciatic foramen supe- The coccyx is attached inferiorly and is the posterior riorly and the lesser sciatic foramen inferiorly. This is an border of the pelvic outlet. important location for identifying the course of the puden- Attached to the sacrum are the ilium, ischium, and pubic dal nerve, artery, and vein, and will be discussed later in rami. Several landmarks are important to the pelvic the chapter. 79 80 Anatomic Correlates Anterior Inferior Pubic Ramus Superior Acetabulum Ischial lliac Spine Tuberosity Pubic Symphysis Sacrospinous Sacrospinous Ligament Ligament Sacrospinous Ligament (cut) Coccyx a b Figure 4-2.1. Bones and ligaments of the pelvis. a, Front view; b, lithotomy view. (Reprinted with the permission of The Cleveland Clinic Foundation.) Muscles of the Pelvic Sidewalls and Pelvic Floor The obturator internus and piriformis make up the pelvic sidewalls. The obturator membrane is a fibrous membrane that covers the obturator foramen. The obturator internus muscle lies on the superior (intrapelvic) side of the obtu- rator membrane. The obturator internus origin is on the Sacral Promontory Greater inferior margin of the superior pubic ramus and the pelvic Sciatic Foramen surface of the obturator membrane. Its tendon passes Anterior through the lesser sciatic foramen to insert onto the greater Superior lliac Spine trochanter of the femur to laterally rotate the thigh. The obturator internus receives its innervation from the obtu- rator nerve originating from L5-S2. The obturator vessels and nerve pass through the anterior and lateral border of the obturator membrane to their destination in the adduc- tor compartment of the leg. The piriformis is part of the pelvic sidewall and is Sacrospinous Ligament located dorsal and lateral to the coccygeus. It extends from the anterolateral sacrum to pass through the greater sciatic foramen and insert on the greater trochanter. Lying on top Sacrotuberous of the piriformis is a particularly large neurovascular Ligament Obturator plexus, the lumbosacral plexus. Foramen There is a linear thickening of the fascial covering of Lesser Sciatic the obturator internus muscle called the arcus tendineus Foramen Ischial Ischial Spine levator ani. This thickened fascia forms an identifiable line Tuberosity from the ischial spine to the posterior surface of the ipsi- lateral pubic ramus. The muscles of the levator ani origi- nate from this musculofascial attachment (Figure 4-2.3). The skeletal muscles of the pelvic floor include the Figure 4-2.2. Bones and ligaments of the pelvis (sagittal view).The dashed line repre- levator ani muscles, the coccygeus muscle, the external sents the vertical plane of the anterior superior iliac spine and pubic symphysis. The arrows represent the distribution of weight of the spinal column and abdominal anal sphincter, the striated urethral sphincter, and the contents and along the ilium. (Reprinted with the permission of The Cleveland Clinic superficial perineal muscles (bulbocavernosus, ischiocav- Foundation.) ernosus, and transverse perinea). The levator ani muscle Genital Anatomic Correlates 81 tribute to fecal continence. Some of the fibers of the muscle may blend with the muscularis of the vagina and rectum. The pubococcygeus has a similar origin, but inserts in the Ischial Spine midline onto the anococcygeal raphe and the anterolateral borders of the coccyx. The iliococcygeus extends along the arcus tendineus levator ani from the pubis to the ischial Piriformus Muscle spine to insert in the midline onto the anococcygeal raphe. The coccygeus, although not part of the levator ani, does make up the posterior part of the pelvic floor and has a role Arcus Tendineus Levator Ani in support. Its origin is on the ischial spine and sacrospinous ligament. It inserts on the lateral lower Coccygeus sacrum and coccyx and overlies the sacrospinous ligament. Muscle The muscle becomes thin and fibrous with age. The coc- cygeus often blends with the sacrospinous ligament and, Ileococcygeus because they have the same origin and insertion, it can be Muscle difficult to distinguish the two. Anococcygeal Pubic The space between the levator ani musculature through Raphe Symphasis which the urethra, vagina, and rectum pass is called the Pubococcygus and Puborectalis levator hiatus. The fusion of levator ani where they meet in Arcus Tendineus External Anal Sphincter Perineal Fascia Pelvis the midline creates the levator plate.The levator plate forms Membrane the basis for pelvic support as will be discussed in detail later in this chapter. The levator ani may be very thin and atten- Figure 4-2.3. Muscles of the pelvis (sagittal view). (Reprinted with the permission of The uated, especially in patients with pelvic organ prolapse. Cleveland Clinic Foundation.) Nerves of the Pelvis complex consists of the puborectalis, pubococcygeus, and Although the muscles of the pelvic floor were initially iliococcygeus muscles (Figure 4-2.4). thought to have innervation both from direct branches of The puborectalis has an attachment to the posterior infe- the sacral nerves on the pelvic surface and via the puden- rior pubic rami and arcus tendineus levator ani. Its fibers dal nerve on the perineal surface, recent anatomic, neuro- pass posteriorly forming a sling around the vagina, rectum, physiologic,and experimental evidence indicates that these and perineal body to form the anorectal angle and con- standard descriptions are inaccurate and that the levator ani muscles are innervated solely by a nerve traveling on the superior (intrapelvic) surface of the muscles without contribution of the pudendal nerve1,2 (Figure 4-2.5). Barber et al.1 performed systematic cadaver dissections to characterize the nerve supply to the pelvic floor muscles. Pubococcygeus Urethra Vagina The nerve supplying the coccygeus muscle and the levator Muscle Arcus Tendineus Cooper’s Ligament Fascia Pelvis ani muscles (all three) originates from S3,S4,and/or S5.The Obturator Obturator Canal and nerve exits the foramina and travels 2 to 3cm medial to the Internus Neurovascular Bundle Muscle and ischial spine and arcus tendineus levator ani across the Fascia Arcus coccygeus, iliococcygeus, pubococcygeus, and puborectalis Tendineus muscles.