Learning Objectives (48/80) -- Anatomy & Physiology

Learning Objectives By the end of this section, you will be able to: Describe the bones of the pelvic girdle, and describe how the pelvis unites the lower limbs with the axial skeleton. - Describe how the features of the pelvis differ between the adult male and female pelvis - Describe the ligaments of the pelvis The two hip bones (also called coxal bones or os coxae) are together called the pelvic girdle (hip girdle) and serve as the attachment point for each lower limb. When the two hip bones are combined with the sacrum and coccyx of the axial skeleton, they are referred to as the pelvis. The right and left hip bones also converge anteriorly to attach to each other at the pubic symphysis (Figure 8.3.1). 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 the weight bearing lower limb(s). Thus, the immobility of the pelvis provides a strong foundation for the upper body as it rests on top of the mobile lower limbs. Hip Bone The hip (or coxal) bones form the pelvic girdle portion of the pelvis. The hip bones are 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 (Figure 8.3.2). These names are retained and used to define the three regions of the adult hip bone. The ilium is the fan-like, superior region that forms the largest part of the hip bone. It is firmly united to the sacrum at the largely immobile sacroiliac joint (see Figure 8.3.1). The ischium forms the posteroinferior region of each hip bone. It supports the body when sitting. The pubis forms the anterior portion of the 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. Ilium When you place your hands on your waist, you can feel the arching, superior margin of the ilium along your waistline (see Figure 8.3.2). This curved, superior margin of the ilium is the iliac crest. The rounded, anterior termination of the iliac crest is the anterior superior iliac spine. This important bony landmark can be felt at your anterolateral hip. Inferior to the anterior superior iliac spine is a rounded protuberance called the anterior inferior iliac spine. Both of these iliac spines serve as attachment points for muscles of the thigh. Posteriorly, the iliac crest curves downward to terminate as the posterior superior iliac spine. Muscles and ligaments surround but do not cover this bony landmark, thus sometimes producing a depression seen as a “dimple” located on the lower back. M