41.4: Pelvis

Structure

The pelvis if formed by the sacrum posteriorly and the paired hip or innominate bones on each side, which unite anteriorly. Each hip bone is formed from three smaller, fused parts:

  • The ilium is the large part which forms the iliac crests and the sacroiliac joint.
  • The ischium is the smaller posterior part, containing the ischial tuberosity and the ischial spine
  • The pubis is the small anterior portion, which joins with the contralateral bone at the pubic symphysis.

All three bones contribute the the acetabulum or hip joint, a circular depression on the external and lateral part of the hip bone.

Important landmarks of the male pelvis include:

  • The iliac crest is a broad, curved plate of bone that extends from the anterior superior iliac spine to the posterior superior iliac spine (top of the sacroiliac joint). The inguinal ligament runs from the anterior superior iliac spine to the pubic tubercule and is another important landmark.
  • The obturator foramen is a hole that is formed between the ischium and the pubis. The obturator membrane/ligament covers most of the foramen in life, but a small hole on the lateral side exists for the passage of the obturator vessels and nerve.
  • The ischial spine divides the inferior surface of the ilium and ischium into the greater and lesser sciatic notches. The sacrospinal and sacrotuberus ligaments complete these notches, converting them into the greater and lesser sciatic foramen. The greater sciatic foramen contains the piriformis and obturator internus muscles, the sciatic nerve, the pudendal neurovascular structures and the superior and inferior gluteal neurovascular structures. The lesser sciatic foramen allows the internal pudendal vessels to enter into the perineum.

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