Pelvic Bone

The pelvic girdle, or hip girdle, is made up of two hip bones, also known as coxal or pelvic bones (os coxa). These bones connect at the pubic symphysis joint in the front and join with the sacrum at the sacroiliac joints in the back. Together, the hip bones, pubic symphysis, sacrum, and coccyx create a deep, basin-like structure known as the bony pelvis. This structure provides strong, stable support for the vertebral column and protects pelvic and lower abdominal organs. The pelvic girdle also connects the lower limb bones to the axial skeleton. In newborns, each hip bone consists of three separate bones—the ilium (superior), pubis (inferior and anterior), and ischium (inferior and posterior)—which are joined by cartilage. By age 23, these bones fuse into a single hip bone, though anatomists still refer to each part individually.

1.0Bones of Pelvic Girdle 

Pelvic girdle is formed by:

• Two Hip bones
• Sacrum 
• Coccyx
• The pelvic cavity lodges and protects the reproductive organs, nerves and blood vessels of the lower limb, urinary bladder and terminal part of the large intestine. 
• The combined weight of trunk, head and upper limbs rests on the pelvis at its articulation with 5th lumbar vertebra.

• Hip Bones (Os Coxae): It consists of 3 parts-ilium, ischium and pubis which are 3 separate bones in early life. The line of union of 3 parts is in the acetabular cavity, which is a deep socket for articulation with the head of the femur to form a hip joint.

2.0Ilium 

• The ilium (IL-e¯-um  flank), the largest of the three components of the hip bone , is composed of a superior ala (wing) and an inferior body. 
• The body is one of the components of the acetabulum, the socket for the head of the femur. 
• The superior border of the ilium, the iliac crest, ends anteriorly in a blunt anterior superior iliac spine. 
• Bruising of the anterior superior iliac spine and associated soft tissues, such as occurs in body contact sports, is called a hip pointer. 
• Below this spine is the anterior inferior iliac spine. Posteriorly, the iliac crest ends in a sharp posterior superior iliac spine. Below this spine is the posterior inferior iliac spine. 
• The spines serve as points of attachment for the tendons of the muscles of the trunk, hip, and thighs. 
• Below the posterior inferior iliac spine is the greater sciatic notch (sı¯-AT-ik), through which the sciatic nerve passes, along with other nerve and muscles. 
• The sciatic nerve is the longest nerve in the body, passes. The medial surface of the ilium contains the iliac fossa, a concavity where the tendon of the iliacus muscle attaches. 
• Posterior to this fossa are the iliac tuberosity, a point of attachment for the sacroiliac ligament, and the auricular surface (auric-  ear-shaped), which articulates with the sacrum to form the sacroiliac joint . 
• Projecting anteriorly and inferiorly from the auricular surface is a ridge called the arcuate line (AR-kuˉ-aˉt; arc-  bow). 
• The other conspicuous markings of the ilium are three arched lines on its lateral surface called the posterior gluteal line (glut-  buttock), the anterior gluteal line, and the inferior gluteal line. The gluteal muscles attach to the ilium between these lines.

3.0Ischium 

• The ischium (IS-ke¯-um  hip), the inferior, posterior portion of the hip bone , comprises a superior body and an inferior ramus (ram-  branch; plural is rami). 
• The ramus is the portion of the ischium that fuses with the pubis. Features of the ischium include the prominent ischial spine, a lesser sciatic notch below the spine, and a rough and thickened ischial tuberosity. 
• Because this prominent tuberosity is just deep to the skin, it commonly begins hurting after a relatively short time when you sit on a hard surface. 
• Together, the ramus and the pubis surround the obturator foramen (OB-too-raˉ-toˉr; obtur-  closed up), the largest foramen in the skeleton. 
• The foramen is so named because, even though blood vessels and nerves pass through it, it is nearly completely closed by the fibrous obturator membrane.

4.0Pubis

• The pubis (PU¯-bis; plural is pubes), meaning pubic bone, is the anterior and inferior part of the hip bone . 
• A superior ramus, an inferior ramus, and a body between the rami make up the pubis. The anterior, superior border of the body is the pubic crest, and at its lateral end is a projection called the pubic tubercle. 
• This tubercle is the beginning of a raised line, the pectineal line (pekTIN-e¯-al), which extends superiorly and laterally along the superior ramus to merge with the arcuate line of the ilium. 
• These lines, as you will see shortly, are important landmarks for distinguishing the superior (false) and inferior (true) portions of the bony pelvis. 
• The pubic symphysis is the joint between the two pubes of the hip bones. It consists of a disc of fibrocartilage. Inferior to this joint, the inferior rami of the two pubic bones converge to form the pubic arch. In the later stages of pregnancy, the hormone relaxin (produced by the ovaries and placenta) increases the flexibility of the pubic symphysis to ease delivery of the baby. 
• Weakening of the joint, together with an already altered center of gravity due to an enlarged uterus, also changes the mother’s gait during pregnancy. 
• The acetabulum (as-e-TAB-uˉ-lum  vinegar cup) is a deep fossa formed by the ilium, ischium, and pubis. 
• It functions as the socket that accepts the rounded head of the femur. Together, the acetabulum and the femoral head form the hip (coxal) joint. 
• On the inferior side of the acetabulum is a deep indentation, the acetabular notch, that forms a foramen through which blood vessels and nerves pass and serves as a point of attachment for ligaments of the femur (for example, the ligament of the head of the femur).

5.0Articulated Pelvis 

Each hip bone articulates behind with the sacrum, forming Sacro-iliac joint and in front with its fellow opposite side at the Pubic symphysis.

Pelvis is divided into 2 parts by the Pelvic brim:

• True pelvis or Pelvis minor: lies below pelvic brim.
• False pelvis or Pelvis major: lies above pelvic brim.

Pelvic brim is formed by 

• Sacral promontory
• Arcuate line of the sacrum and ilium 
• Iliopectineal line
• Pubic crest and 
• Upper end of Pubic symphysis

False and True Pelvis 

• The bony pelvis is divided into superior and inferior portions by a boundary called the pelvic brim that forms the inlet into the pelvic cavity from the abdomen . 
• You can trace the pelvic brim by following the landmarks around parts of the hip bones to form the outline of an oblique plane. 
• Beginning posteriorly at the sacral promontory of the sacrum, trace laterally and inferiorly along the arcuate lines of the ilium. Continue inferiorly along the pectineal lines of the pubis. 
• Finally, trace anteriorly along the pubic crest to the superior portion of the pubic symphysis. 
• Together, these points form an oblique plane that is higher in the back than in the front. The circumference of this plane is the pelvic brim. 
• The portion of the bony pelvis superior to the pelvic brim is referred to as the false (greater) pelvis . 
• It is bordered by the lumbar vertebrae posteriorly, the upper portions of the hip bones laterally, and the abdominal wall anteriorly. 
• The space enclosed by the false pelvis is part of the lower abdomen; it contains the superior portion of the urinary bladder (when it is full) and the lower intestines in both genders and the uterus, ovaries, and uterine tubes of the female. 
• The portion of the bony pelvis inferior to the pelvic brim is the true (lesser) pelvis . It has an inlet, an outlet, and a cavity. 
• It is bounded by the sacrum and coccyx posteriorly, inferior portions of the ilium and ischium laterally, and the pubic bones anteriorly. 
• The true pelvis surrounds the pelvic cavity. The true pelvis contains the rectum and urinary bladder in both genders, the vagina and cervix of the uterus in females, and the prostate in males. 
• The superior opening of the true pelvis, bordered by the pelvic brim, is called the pelvic inlet; the inferior opening of the true pelvis is the pelvic outlet, which is covered by the muscle at the floor of the pelvis. 
• The pelvic axis is an imaginary line that curves through the true pelvis from the central point of the plane of the pelvic inlet to the central point of the plane of the pelvic outlet.