This section describes the pelvis and its structures.

The Pelvis

• Pelvis- comprises two hipbones (os coxae) connected anteriorly with the symphysis pubis and posteriorly with the sacrum. It also has two notches called acetabulars creating joints with the femur. It also has two joints that allow flexibility with the spine and femurs.

Fig. 1(Gray's Anatomy)

Fig. 2 (Gray's Anatomy)

Fig. 3 (Gray's Anatomy)

• Functionality- it is the primary means of transmitting the body's weight to the lower extremities. Very little movement is possible between the hip and the sacrum. The pelvis then acts like a single unit in normal body movements. The movements of the pelvis are closely linked with the movements of the vertebral column. Changes in the pelvis occur with various body movements especially with the lumbar vertebrae and the hip joints. Its over all designs allows for walking erect, for females to give birth, and creates a stable structure for the base of the lower abdominal organs and organ systems.

Bone formation of the pelvis

• The upper formation of the pelvis is basically called the ilium. However, the ilium is broken into several different anatomical regions. To begin with, one starts with the posterior superior iliac spine. This is the section of the ilium, which merges the left and right ileum's to the sacro-iliac joint. The upper most region of the ilium is know as the iliac crest. This is a landmark used extensively in health care and especially in anesthesia to begin to identify L4 for spinal anesthesia. Next comes the anterior superior ilium to the anterior inferior ilium. This region then forms a diagonal or arcuate line, which separates the pelvis into upper and lower pelvis.

• The lower pelvis is know as the ischium. It has two main features that stand out.

• The medial aspect of the ischium begins with the pubic crest that connects left and right coxae. Then going posteriorly begins the ramus of the pubis and the ramus of the ischium. The main stand out feature is the obturator foramen.

• The lateral ischium consists of anteriorly the pubis going back to the ischial tuberosity. The main stand out feature is the acetabular notch. This is the base for the hip joint, which connects the pelvis to the legs.

Fig. 4 (Gray's Anatomy)

Fig. 5 (Gray's Anatomy)

Fig. 6 (Gray's Anatomy)

Muscle and ligament roots in the pelvis

As previously mentioned, the pelvis is a structural unit which provides stability for the body. It provides this structure by anchoring muscle and tendons.

•  Muscles anchored in the lateral pelvis-going from posterior to anterior they are the following list: adductor magnus, gemellus inferior, gluteus medius, gluteus maximus, latissimus dorsi, gluteus minimus, external oblique, tensor fasciae latae, rectus femorus, obturator externus, pectineus, rectus abdominus, adductor longus, adductor brevis, and gracilis.

•  Muscles anchored in the medial pelvis are the following: sartorius, transversus abdominus, quadratus lumborum, erector spinae, obturator internus, and sphincter urethrae.

•  The ligaments attached to the pelvis are the following: sacrospinous ligament and the sacrotuberous ligament.

•  Joints of the pelvis comprise the sacro-iliac joint and the symphysis pubis.

Sacro-iliac joint comprises numerous ligaments that provide flexibility and stability.

•  The interosseous and posterior sacro-iliac ligaments combined with the anterior sacro-iliac ligament allow flexion with the vertebral column while producing flexion with the sacrum on the hips. The stress of these movements is carried through these ligaments.

•  The sacrotuberous and the sacrospinous ligaments prevent forward and downward tilting of the sacrum with the hips.

•  The last ligament is the iliolumbar ligament, which limits forward movement at sacro-iliac joint.

•  Overall the entire complex of ligaments allows the displacement of weight through the sacro-iliac joint, thus preventing overt tilting of the vertebral column, and allowing erect structure stability.

Symphysis Pubis is a cartilage based join that connects the anterior pubis of left and right coxae. This joint only becomes flexible in the female pelvis during pregnancy. In the later stages of pregnancy, this joint separates to enlarge the birth canal.

Fig. 7 (Gray's Anatomy)

Vasculature and Nerves of the Pelvis

•  The arterial blood flow of the pelvis begins with the distal end of the abdominal aorta. This breaks into two common iliac arteries. One aspect of the artery branches forming the inferior vena cava. The other breaks into two branches the internal iliac arteries and the external iliac arteries.

•  The internal iliac artery is the branch that feeds blood to the pelvis and pelvic wall. The chief extra pelvic branches are the superior gluteal, inferior gluteal, and internal pudendal and obturator arteries. The other branches of the internal iliac feed various lower abdominal organs such as the rectal artery that feeds the anal canal and then feeds the labia and clitoris in females and in male's forms the deep artery of the penis. The internal iliac also feeds the upper bladder with the superior vesical artery which also feeds the uterus as it turns into the uterine artery and the vaginal artery. The inferior vesical artery feeds the lower bladder.

•  The external iliac artery is the main arterial supply of the lower limb by forming the femoral artery. The external artery does have a few branches of importance to the pelvis. The deep circumflex artery feeds the inguinal ligament and the superior iliac spine and crest. The Inferior epigastric artery feeds the rectus abdominus muscle.

Fig. 8 (Gray's Anatomy)	Fig. 9 (Gray's Anatomy)
Fig. 10 (Gray's Anatomy)	Fig. 11 (Gray's Anatomy)

•  The peripheral nervous system of the pelvic region is formed from the lumbar plexus. Nerve roots 2,3, and 4 form the left and right femoral nerves. All the lumbar plexus L1- C1 have various branches that supplies inervation to the lower abdominal organs and the pelvis.

Basic Study Questions

  1.  What is the function of the pelvis?

  2.  Locate the ilium and ischium.

  3.  What are the 2 joints of the pelvis?

Additional Study Questions