8.3

The Pelvic Girdle and Pelvis

Learning Objectives

  • Define the pelvic girdle and describe the bones and ligaments of the pelvis.

  • Explain the three regions of the hip bone and identify their bony landmarks.

  • Describe the openings of the pelvis and the boundaries of the greater and lesser pelvis.

Overview of the Pelvic Girdle

  • The pelvic girdle, also known as the hip girdle, is formed by a single bone, the hip bone or coxal bone.

    • Coxal translates to "hip."

  • The hip bone serves as the attachment point for each lower limb.

  • Each hip bone is firmly joined to the axial skeleton via its articulation with the sacrum of the vertebral column.

  • The right and left hip bones converge anteriorly to attach to each other.

  • The bony pelvis is the complete structure formed by:

    • The two hip bones

    • The sacrum

    • The coccyx (attached inferiorly to the sacrum)

  • Differences from the Pectoral Girdle:

    • Unlike the highly mobile pectoral girdle, the pelvic girdle is a largely immobile, weight-bearing structure.

    • Its strong unity enables the weight of the body to be transferred laterally from the vertebral column through the pelvic girdle and hip joints to either lower limb when the other limb is not bearing weight.

    • The immobility of the pelvis provides a solid foundation for the upper body resting on the mobile lower limbs.

Hip Bone Structure

  • The hip bone or coxal bone forms part of the pelvic girdle.

  • The paired hip bones are large, curved bones forming the lateral and anterior aspects of the pelvis.

  • Each adult hip bone is formed by three separate bones:

    • Ilium

    • Ischium

    • Pubis

  • These three components fuse together during the late teenage years to form the adult hip bone.

Regions of the Hip Bone

  • Ilium:

    • The fan-shaped, superior portion forms the largest part of the hip bone.

    • Firmly united to the sacrum at the largely immobile sacroiliac joint.

    • Bony Landmarks:

    • Iliac Crest:

      • The superior margin of the ilium that can be felt at the waistline.

    • Anterior Superior Iliac Spine:

      • The rounded, anterior termination of the iliac crest that is easily palpated.

    • Anterior Inferior Iliac Spine:

      • Rounded protuberance inferior to the anterior superior iliac spine, serves as a muscle attachment point.

    • Posterior Superior Iliac Spine:

      • Terminates the iliac crest posteriorly.

    • Posterior Inferior Iliac Spine:

      • Located at the inferior end of the auricular surface of the ilium, assists in sacroiliac joint support.

    • Iliac Fossa:

      • A shallow depression on the anteromedial surface of the upper ilium.

    • Greater Sciatic Notch:

      • Located along the posteriormargin; an inverted U-shaped indentation.

  • Ischium:

    • Forms the posterolateral portion of the hip bone.

    • Bony Landmarks:

    • Ischial Tuberosity:

      • A large, roughened area of the inferior ischium that supports body weight when sitting.

    • Ischial Ramus:

      • A narrow segment of bone projecting superiorly and anteriorly from the ischial tuberosity.

    • Lesser Sciatic Notch:

      • Slightly curved margin above the ischial tuberosity.

    • Ischial Spine:

      • The bony projection separating the lesser from the greater sciatic notch.

  • Pubis:

    • Forms the anterior portion of the hip bone.

    • Bony Landmarks:

    • Pubic Body:

      • The enlarged medial portion.

    • Pubic Tubercle:

      • A small bump located superiorly on the pubic body.

    • Superior Pubic Ramus:

      • A segment of bone that extends laterally from the pubic body to join the ilium.

    • Pectineal Line:

      • The narrow ridge along the superior margin of the superior pubic ramus.

    • Pubic Symphysis:

      • The joint where the bodies of opposite hip bones are joined.

    • Inferior Pubic Ramus:

      • Extends downward to join the ischial ramus, forming the ischiopubic ramus.

    • Subpubic Angle:

      • The angle formed at the pubic symphysis by the ischiopubic rami from both sides.

Functions of the Pelvis

  • Composed of four bones: right and left hip bones, sacrum, coccyx.

  • Functions:

    • Support the weight of the upper body when sitting.

    • Transfer weight to the lower limbs while standing.

    • Serve as an attachment point for trunk and lower limb muscles.

    • Protect internal pelvic organs.

  • Anatomical Position:

    • When standing: the pelvis is tilted anteriorly, with the anterior superior iliac spines and the pubic tubercles in the same vertical plane.

    • The anterior (internal) surface of the sacrum faces forward and downward.

Anatomy of the Pelvic Openings

  • The three areas of each hip bone converge to form a deep, cup-shaped cavity known as the acetabulum (part of the hip joint).

  • The large opening between the ischium and pubis is the obturator foramen, primarily filled with connective tissue.

  • Ligaments of the Pelvis:

    • The sacroiliac joint is supported by:

    • Anterior Sacroiliac Ligament:

      • Located on the anterior side.

    • Posterior Sacroiliac Ligament:

      • Located on the posterior side.

    • Additional ligaments that support and immobilize the sacrum are:

    • Sacrospinous Ligament:

      • Runs from the sacrum to the ischial spine.

    • Sacrotuberous Ligament:

      • Runs from the sacrum to the ischial tuberosity.

    • Together, these ligaments help support the weight carried by the sacrum.

Sciatic Foramina

  • The sacrinal ligaments also help define two openings in the pelvis through which muscles, nerves, and blood vessels exit:

    • Greater Sciatic Foramen:

    • Formed by the greater sciatic notch of the hip bone, the sacrum, and the sacrospinous ligament.

    • Lesser Sciatic Foramen:

    • Formed by the lesser sciatic notch, along with the sacrospinous and sacrotuberous ligaments.

Division of the Pelvis

  • The enclosed space of the bony pelvis is divided into two regions:

    • Greater Pelvis (Greater Pelvic Cavity or False Pelvis):

    • Broad and superior region defined laterally by the large upper hip bone.

    • Occupied by portions of the small and large intestines; associated closely with the abdominal cavity.

    • Lesser Pelvis (Lesser Pelvic Cavity or True Pelvis):

    • Narrower and located inferiorly, containing the bladder and other pelvic organs.

    • Pelvic brim (Pelvic inlet):

      • Superior margin that separates the greater and lesser pelvis, defined by:

      • Upper margin of the pubic symphysis (anterior)

      • Pectineal line of the pubis

      • Arcuate line of the ilium

      • Sacral promontory (posterior)

    • Pelvic Outlet:

      • Inferior limit defined by:

      • Inferior margin of the pubic symphysis (anterior)

      • Ischiopubic ramus, ischial tuberosity, sacrotuberous ligament, inferior tip of the coccyx (posterior).

    • The anteroinferior to posteroinferior orientation of the lesser pelvis is due to the anterior tilt of the pelvis.

Comparison of Female and Male Pelvis

  • Differences relate to function (e.g., adaptation for childbirth) and body size:

  • Female Pelvis:

    • Lighter, thinner bones.

    • Round or oval-shaped pelvic inlet.

    • Shorter, wider lesser pelvic cavity.

    • Greater than 80 degrees subpubic angle.

    • Rounded and larger pelvic outlet.

  • Male Pelvis:

    • Thicker, heavier bones.

    • Heart-shaped pelvic inlet.

    • Longer, narrower lesser pelvic cavity.

    • Less than 70 degrees subpubic angle.

    • Smaller pelvic outlet.

  • Forensic Implications:

    • The differences in hip bone characteristics are significant for sex determination in forensic pathology.