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The pelvic girdle (hip girdle) is formed by a single bone, the hip bone or coxal bone (coxal = “hip”), which serves as the attachment point for each lower limb. Each hip bone, in turn, is firmly joined to the axial skeleton via its attachment to the sacrum of the vertebral column. The right and left hip bones also converge anteriorly to attach to each other. The bony pelvis is the entire structure formed by the two hip bones, the sacrum, and, attached inferiorly to the sacrum, the coccyx ( [link] ).
Unlike the bones of the pectoral girdle, which are highly mobile to enhance the range of upper limb movements, the bones of the pelvis are strongly united to each other to form a largely immobile, weight-bearing structure. This is important for stability because it enables the weight of the body to be easily transferred laterally from the vertebral column, through the pelvic girdle and hip joints, and into either lower limb whenever the other limb is not bearing weight. Thus, the immobility of the pelvis provides a strong foundation for the upper body as it rests on top of the mobile lower limbs.
The hip bone, or coxal bone , forms the pelvic girdle portion of the pelvis. The paired hip bones are the large, curved bones that form the lateral and anterior aspects of the pelvis. Each adult hip bone is formed by three separate bones that fuse together during the late teenage years. These bony components are the ilium, ischium, and pubis ( [link] ). These names are retained and used to define the three regions of the adult hip bone. The pubis curves medially, where it joins to the pubis of the opposite hip bone at a specialized joint called the pubic symphysis .
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.
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.
| Overview of Differences between the Female and Male Pelvis | ||
|---|---|---|
| Female pelvis | Male pelvis | |
| Pelvic weight | Bones of the pelvis are lighter and thinner | Bones of the pelvis are thicker and heavier |
| Pelvic inlet shape | Pelvic inlet has a round or oval shape | Pelvic inlet is heart-shaped |
| Lesser pelvic cavity shape | Lesser pelvic cavity is shorter and wider | Lesser pelvic cavity is longer and narrower |
| Subpubic angle | Subpubic angle is greater than 80 degrees | Subpubic angle is less than 70 degrees |
| Pelvic outlet shape | Pelvic outlet is rounded and larger | Pelvic outlet is smaller |
The pelvic girdle, consisting of a hip bone, serves to attach a lower limb to the axial skeleton. The hip bone articulates posteriorly at the sacroiliac joint with the sacrum, which is part of the axial skeleton. The right and left hip bones converge anteriorly and articulate with each other at the pubic symphysis. The combination of the hip bone, the sacrum, and the coccyx forms the pelvis. The pelvis has a pronounced anterior tilt. The primary function of the pelvis is to support the upper body and transfer body weight to the lower limbs. It also serves as the site of attachment for multiple muscles.
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