BONY PELVIS

By Oba Mike

Image credit: sites.google. com

Introduction

The bony pelvis or simply pelvis is a basin-like structure composed of the hip bones, pubic symphysis, sacrum and coccyx.

Functionally, the pelvis provides support to the vertebral column, pelvic and lower abdominal organs. It also connects the bones of the lower limbs to the axial skeleton.

Functions of the Pelvis

1. Supports the vertebral column.

2. Protects pelvic and lower abdominal organs.

3. Connects the bones of the lower limbs to the axial skeleton.

4. Transmits the weight of the body to the lower limbs while standing and to the seat while sitting.

5. Helps in the attachment of several muscles.

6. Supports childbearing in females.

Components of the Bony Pelvis

The bony pelvis is formed by four different structures:

1. 2 hip bones (pelvic girdle)

2. Pubic symphysis 

3. Sacrum

4. Coccyx

Hip bones

The hip bones also called pelvic or coxal bones are the two bones that form the pelvic girdle. They form the anterior and lateral part of the bony pelvis. 

Both bones unite anteriorly at the pubic symphysis.

They also form a joint posteriorly with the sacrum called sacroiliac joint . 

Parts of the hip bone

The hip bone is actually not a single bone. In a new born, it consist of three bones separated by cartilage. In an adult above 23 years, these bones are totally fused with no visible landmarks to differentiate them. 

For easy description, we'll discuss the hipbone through the 3 individual bones that forms it.

The three bones include:

a. Ilium

b. Ischium

c. Pubis

Ilium

The ilium is the largest of the three components of the hip bone and forms the superior and lateral parts of it.

The most superior portion of the ilium called iliac crest can be felt whe you holf your waist (arms akimbo).

The iliac crest ends anteriorly at the Anterior Superior Iliac Spine. Below the ASIS is the Anterior inferior Iliac spine.

The iliac crest also ends posteriorly at the Posterior Superior Iliac Spine. Below this spine again is the Posterior Inferior Iliac spine. PLS VIEW PICTURES TO SEE THESE LANDMARKS.

The spines are points of attachments for muscles of the trunk, hips and thighs.

Below the posterior inferior iliac spine is the Greater sciatic notch which is a passageway for the sciatic nerve ( the longest nerve in the body).

At the medial surface of the ilium is the iliac fossa, a concavity where the tendons of the iliacus muscle attaches. 

Posterior to this fossa is the iliac tuberosity, a point of attachment for the sacroiliac ligament and the auricular surface which articulates with the sacrum to form the sacroiliac joint.

Projecting anteriorly and inferiorly from the auricular surface is a ridge called arcuate line. 

Also noticeable in the ilium are the anterior, posterior and inferior gluteal lines which are points of attachments for the gluteal muscles.

The ilium articulates with the other two bones at the acetabulum.

Ischium

The Ischium is the posterior inferior portion of the hip bone.  It consist of a superior body and an inferior ramus(branch).

The ramus is the portion of the ischium that fuses with the pubis.

Features of the ischium include the prominent ischial spine which is an important landmark for pudendal block during labour.  Inferior to this spine is the lesser sciatic notch which is a passageway for pudendal vessels.

Another prominent feature of the ischium is the ischial tuberosity, a site for muscle attachment. The ischial tuberosity bears the weight of the body while sitting and can hurt when you sit for long on a hard surface.

Together, the ischial ramus and the pubis surround the obturator foramen, a passageway for blood vessels and nerves. The foramen is almost covered totally by the obturator membrane.

Pubis

The pubis is the anterior inferior portion of the hipbone. It consist of a body and two rami(branches) which are the superior and inferior rami.

The anterior superior portion of the bone is the pubic crest which ends laterally at the pubic tubercle.

The pubic tubercle is the beginning of a raised line called pectineal line which joins with the arcuate line of the ilium.

The pubic symphysis is the joint between the two pubic bones. It is a fibrocartilaginous joint..

Inferior to the articulating surface of this joint is the pubic arch which forms the subpubic angle use in determining the sex of someone from skeletal remains.

The three bones meet to form a deep fossa called acetabulum. It functions as the socket that accepts the ball head of the femur. 

Together, the acetabulum and the femoral head form the hip(coxal) joint.

True and false pelvis

Click on the diagram to have a better view or use the slides

The bony pelvis is divided into superior and inferior portions by a boundary called the pelvic brim or inlet You can trace the pelvic brim by following the landmarks around parts of the hip bone.

 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(see picture). 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.

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. 

During childbirth the pelvic axis is the route taken by the baby’s head as it descends through the pelvis.

More pictures in the slides

ASSIGNMENT

Write on the sacrum and coccyx.

Submit on or before Friday.