What is the Pelvic Girdle?

A single bone, the hip bone or coxal bone (coxal = “hip”), forms the pelvic girdle (hip girdle), which acts as the attachment point for each lower limb. Each hip bone is firmly attached to the axial skeleton through its connection to the sacrum of the vertebral column. Both the right and left hip bones converge anteriorly to connect. The bony pelvis is made up of the two hip bones, the sacrum, and the coccyx, which are attached inferiorly to the sacrum.

Hip Bone

The pelvic girdle is formed by the hip bone, also known as the coxal bone. The broad, curved bones that make up the lateral and anterior aspects of the pelvis are known as the paired hip bones. Each adult hip bone is made up of three separate bones that join in late adolescence. The ilium, ischium, and pubis are the bony components in question. The three areas of the adult hip bone are still referred to by these names.

Parts of the Hip Bone

The ilium is the largest part of the hip bone, with a fan-like superior area. At the largely immobile sacroiliac joint, it is tightly attached to the sacrum. Each hip bone's posteroinferiorly region is formed by the ischium. When seated, it provides support for the body. The pubis is the part of the hip bone that is closest to the front. The pubis bends medially and joins the pubis of the opposing hip bone at the pubic symphysis, a specialized joint.

Ilium

A person can feel the arching, superior margin of the ilium around the waistline if he puts his hands on his waist. The iliac crest is the curved, superior margin of the ilium. The anterior superior iliac spine is the rounded, anterior termination of the iliac crest. At the anterolateral thigh, one can feel this vital bony landmark. A rounded protuberance called the anterior inferior iliac spine is located under the anterior superior iliac spine. The iliac spines act as attachment points for thigh muscles on both sides. The iliac crest curves down posteriorly to form the posterior superior iliac spine.

Muscles and ligaments surround but do not cover this bony landmark, resulting in a depression on the lower back that is often referred to as a “dimple”. The posterior inferior iliac spine is located below. It is at the lower end of the auricular surface of the ilium, which is a wide, roughened region. The sacroiliac joint is formed when the auricular surface of the femur articulates with the auricular surface of the sacrum. The muscles and powerful ligaments that protect the sacroiliac joint bind to both the posterior superior and posterior inferior iliac spines.

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

Ischium

The posterolateral part of the hip bone is formed by the ischium. The ischial tuberosity is a broad, roughened region of the inferior ischium. It is the attachment point for the posterior thigh muscles, and it also bears the body's weight while seated. Wiggle the pelvis against the seat of a chair to feel the ischial tuberosity. The ischial ramus is a short piece of bone that projects superiorly and anteriorly from the ischial tuberosity. The lesser sciatic notch is the strongly curved posterior margin of the ischium above the ischial tuberosity. The ischial spine is the bony projection that separates the lesser and greater sciatic notch.

Pubis

The pubis is the part of the hip bone that is closest to the front. The pubic body is the swollen medial part of the pubis. The pubic tubercle is a small bump located superiorly on the pubic body. The superior pubic ramus is a bone segment that connects the pubic body to the ilium laterally. The pectineal line of the pubis is a thin ridge that runs along the superior margin of the superior pubic ramus.

The pubic symphysis connects the pubic body of one hip bone to the pubic body of the opposite hip bone. The inferior pubic ramus extends backward and laterally from the body. The pubic arch is a bony structure created by the pubic symphysis and the adjacent pubic bones' bodies and inferior pubic rami. The inferior pubic ramus joins the ischial ramus and stretches inward. The ischiopubic ramus connects the pubic body to the ischial tuberosity, forming a single ischiopubic ramus. The subpubic angle appears inverted V-shaped when the ischiopubic rami from both sides meet at the pubic symphysis.

Pelvis

The right and left hip bones, the sacrum, and the coccyx are the four bones that make up the pelvis. The pelvis serves a variety of purposes. Its main function is to support the upper body's weight while sitting and to move the weight to the lower limbs while standing. It protects the internal pelvic organs and acts as an attachment point for trunk and lower limb muscles. The pelvis is bent anteriorly while standing in the anatomical role. The anterior superior iliac spines and pubic tubercles are in the same vertical plane in this location, and the sacrum's anterior (internal) surface faces forward and downward.

The ilium, pubis, and ischium, three areas of each hip bone, converge in the center to form the acetabulum, a deep, cup-shaped cavity. This is part of the hip joint and is found on the lateral side of the hip bone. The obturator foramen is a wide opening between the ischium and the pubis in the anteroinferior hip bone. This area is mostly filled in by connective tissue and acts as a site for muscle connection on both the internal and external surfaces.

The bones of the pelvis are linked by several ligaments. A pair of strong ligaments attached between the sacrum and ilium portions of the hip bone support the relatively immobile sacroiliac joint. On the anterior side of the joint, there is the anterior sacroiliac ligament, and on the posterior side, there is the posterior sacroiliac ligament. Two more ligaments run between the sacrum and the hip bone. From the sacrum to the ischial spine, the sacrospinous ligament runs, and from the sacrum to the ischial tuberosity, the Sacro tuberous ligament runs. The sacrum is supported and immobilized by these ligaments as it bears the weight of the body.

Context and Applications 

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for

• Bachelor of Science in Zoology
• Master of Science in Biochemistry
• Master of Science in Zoology
• Master of Science in Anatomy and Physiology

Related Concepts

• Pelvic girdle
• Pelvic bones
• The appendicular system

Practice Problems

Why are the bones of the pelvis strongly attached?

The bones of the pelvis are closely united to each other to form a relatively immobile, weight-bearing structure, unlike the bones of the pectoral girdle, which are highly flexible to increase the range of upper limb movements. This is vital for stability since it allows the body's weight to be shifted laterally from the vertebral column, through the pelvic girdle and hip joints, and into either lower limb when the other isn't bearing weight. When the upper body sits on top of the mobile lower limbs, the pelvis' immobility provides a solid base.