8.3 The pelvic girdle and pelvis  (Page 2/55)

The shallow depression located on the anteromedial (internal) surface of the upper ilium is called the iliac fossa    . The inferior margin of this space is formed by the arcuate line of the ilium    , the ridge formed by the pronounced change in curvature between the upper and lower portions of the ilium. The large, inverted U-shaped indentation located on the posterior margin of the lower ilium is called the greater sciatic notch    .

Ischium

The ischium forms the posterolateral portion of the hip bone (see [link] ). The large, roughened area of the inferior ischium is the ischial tuberosity    . This serves as the attachment for the posterior thigh muscles and also carries the weight of the body when sitting. You can feel the ischial tuberosity if you wiggle your pelvis against the seat of a chair. Projecting superiorly and anteriorly from the ischial tuberosity is a narrow segment of bone called the ischial ramus    . The slightly curved posterior margin of the ischium above the ischial tuberosity is the lesser sciatic notch    . The bony projection separating the lesser sciatic notch and greater sciatic notch is the ischial spine    .

Pubis

The pubis forms the anterior portion of the hip bone (see [link] ). The enlarged medial portion of the pubis is the pubic body    . Located superiorly on the pubic body is a small bump called the pubic tubercle    . The superior pubic ramus    is the segment of bone that passes laterally from the pubic body to join the ilium. The narrow ridge running along the superior margin of the superior pubic ramus is the pectineal line    of the pubis.

The pubic body is joined to the pubic body of the opposite hip bone by the pubic symphysis. Extending downward and laterally from the body is the inferior pubic ramus    . The pubic arch    is the bony structure formed by the pubic symphysis, and the bodies and inferior pubic rami of the adjacent pubic bones. The inferior pubic ramus extends downward to join the ischial ramus. Together, these form the single ischiopubic ramus    , which extends from the pubic body to the ischial tuberosity. The inverted V-shape formed as the ischiopubic rami from both sides come together at the pubic symphysis is called the subpubic angle    .

Pelvis

The pelvis consists of four bones: the right and left hip bones, the sacrum, and the coccyx (see [link] ). The pelvis has several important functions. Its primary role is to support the weight of the upper body when sitting and to transfer this weight to the lower limbs when standing. It serves as an attachment point for trunk and lower limb muscles, and also protects the internal pelvic organs. When standing in the anatomical position, the pelvis is tilted anteriorly. In this position, the anterior superior iliac spines and the pubic tubercles lie in the same vertical plane, and the anterior (internal) surface of the sacrum faces forward and downward.

The three areas of each hip bone, the ilium, pubis, and ischium, converge centrally to form a deep, cup-shaped cavity called the acetabulum    . This is located on the lateral side of the hip bone and is part of the hip joint. The large opening in the anteroinferior hip bone between the ischium and pubis is the obturator foramen    . This space is largely filled in by a layer of connective tissue and serves for the attachment of muscles on both its internal and external surfaces.