Figure 17-1 is an anatomic section showing the relationships of the major muscles of the pelvis. The levator ani and coccygeus muscles form the floor of the pelvis (pelvic diaphragm). This is the most inferior portion of the body wall and closes the abdominopelvic cavity. The obturator internus and the piriformis muscles originate within the pelvis and thus form part of the pelvic wall, but they are really muscles of the lower limbs.
The endopelvic fascia is the internal investing fascia of the pelvis. Its parietal layer (Fig. 17-2) covers the levator ani, coccygeus, and the intrapelvic portions of the obturator internus and piriformis muscles. It is directly continuous above with the transversalis (endoab-dominal) fascia lining the abdominal cavity. The visceral layer of the endopelvic fascia covers the urinary bladder, lower third of the ureters, uterus, vagina, and the rectum.
Four of the pelvic muscles have important extrapelvic insertions. These are illustrated in Figure 17-3:
1. The psoas major originates from the transverse processes and bodies of the lumbar vertebrae and inserts on the lesser trochanter of the femur.
2. The iliacus originates primarily from the upper two-thirds of the iliac fossa and the ala of the sacrum and inserts with the tendon of the psoas major on the lesser trochanter of the femur. In its common insertion, it comprises the iliopsoas muscle group.
3. The piriformis originates from the sacrum and the margin of the greater sciatic foramen and inserts on the greater trochanter of the femur.
4. The obturator internus originates from the margins of the obturator foramen and inserts on the greater trochanter of the femur.
It is also important to recognize that the pelvic blood vessels lie in front of the pelvic fascia, i.e., superficial to the parietal layer of the endopelvic fascia. The superior and inferior gluteal branches of the internal iliac arteries passing out of the pelvis (Fig. 17-1) must perforate the fascia and carry extensions of the fascia with them to the gluteal region. For example, the fascia of the piri-formis is prolonged outward through the greater sciatic foramen and joins the gluteal fascia. The internal iliac vessels and their branches lie in the subperitoneal tissue in front of the fascia, and the branches to the gluteal region, particularly the superior gluteal artery (the largest branch of the hypogastric artery), emerge in special sheaths of this tissue, paralleling the border of the piri-formis, to reach and supply the gluteus muscles.
In this way, the fascial investments of the iliopsoas, piriformis, and obturator internus muscles and the fascial sheaths of the superior gluteal arteries provide anatomic pathways to the buttocks, hips, and thighs. Superiorly, the pelvic tissues above the levator ani and coccygeus muscles are continuous with the extraperitoneal portion of the abdomen.
Fig. 17—2. Posterior coronal section at level of the rectum showing planes of pelvic fascia (bold lines).
The endopelvic fascia covers the major muscles of the pelvis. The internal iliac arteries Lie superficial to the fascia and then continue within tunneled extensions as they pass to the gluteal region.
(Reproduced from Meyers and Goodman.2)
Fig. 17—3. Extrapelvic insertions of abdominal and pelvic muscles.
The iliopsoas muscle group inserts medially on the lesser trochanter of the femur, and the piriformis and obturator internus insert laterally on the greater trochanter. (Reproduced from Meyers and Goodman.2)
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