Ischial spine—delineates the greater and lesser sciatic notch above and below it. It is the point of fixation for the sacrospinous ligament and the arcus tendineus fascia pelvis (white line); the ischial spine represents an important landmark in the performance of pudendal nerve block and sacrospinous ligament vaginal suspension; vaginal palpation during labor allows detection of progressive fetal descent.
2.
Ischial ramus—joins the pubic rami to encircle the obturator foramen; provides the attachment for the inferior fascia of the urogenital diaphragm and the perineal musculofascial attachments.
3.
Ischial tuberosity—the rounded bony prominence upon which the body rests in the sitting position; a clinical landmark for the passage of the inferior arm of anterior vaginal mesh kit systems.
1.
Body—formed by the midline fusion of the superior and inferior pubic rami.
2.
Symphysis pubis—a fibrocartilaginous symphyseal joint where the bodies of the pubis meet in the midline, allows for some resilience and ﬂexibility, which is critical during parturition.
3.
Superior and inferior pubic rami—join the ischial rami to encircle the obturator foramen; provide the origin for the muscles of the thigh and leg; provide the attachment for the inferior layer of the urogenital diaphragm; the inferior rami is a clinical landmark for transobturator incontinence sling passage.
4.
Pubic tubercle—a lateral projection from the superior pubic ramus, to which the inguinal ligament, rectus abdominis, and pyramidalis attach.
Clinical Considerations Studies using magnetic resonance imaging (MRI) or computed tomography (CT) pelvimetry found an association between the architecture of the bony pelvis, specifically a wider transverse inlet (distance between the most superior aspects of the iliopectineal line) and a shorter obstetric conjugate (shortest distance between the sacral promontory and the pubic symphysis), and the occurrence of pelvic ﬂoor disorders (2,3). A loss of lumbar lordosis and a pelvic inlet that is less vertically oriented is more common in women who develop genital prolapse than in those who do not (4,5). A less vertical orientation of the pelvic inlet is thought to result in an alteration of the intra-abdominal forces that are normally directed anteriorly to the pubic symphysis such that a greater proportion is directed toward the pelvic viscera and their connective tissue and muscular supports. It is theorized that women with a wide pelvic inlet are more likely to develop pelvic organ prolapse (2,3). It is speculated that women with these characteristics may be more likely to suffer neuromuscular and connective tissue injuries during labor and delivery, predisposing them to the development of pelvic neuropathy, pelvic organ prolapse, or both. One MRI study, in which only white women were enrolled to remove race as a potential confounder, found that bony pelvis dimensions were similar at the level of the muscular pelvic ﬂoor with and without pelvic organ prolapse (6).
Pelvic Bone Articulations The pelvic bones are joined by four articulations (two pairs): 1.
Two cartilaginous symphyseal joints—the sacrococcygeal joint and the symphysis pubis—these joints are surrounded by strong ligaments anteriorly and posteriorly, which are responsive to the effect of relaxin and facilitate parturition.
2.
Two synovial joints—the sacroiliac joints—these joints are stabilized by the sacroiliac ligaments, the iliolumbar ligament, the lateral lumbosacral ligament, the sacrotuberous ligament, and the sacrospinous ligament.