Ch17: Pelvic Girdle Flashcards
What four bones make up the pelvic girdle?
- Sacrum
- Coccyx
- 2 Innominate Bones
Innominate bones are also known as the…
Hip bones or os coxae
Each irregularly shaped innominate bone is composed of…
The ilium, the ischium, and the pubis, which are fused together into one bone.
The joints or articulations in the pelvic girdle include the…
Right and left sacroiliac joints posterolaterally, the symphysis pubis anteriorly, and the lumbosacral joint superiorly
Functions of the pelvic girdle (pelvis)
- Most important to movement and posture: supports the weight of the body through the vertebral column and passes that force on to the innominate bones via the sacrum.
- Receives the ground forces generated when the foot contacts the ground and transmits them upward toward the vertebral column.
- During walking, the pelvic girdle moves as a unit in all three planes, allowing relatively smooth motion.
- Supports and protects the pelvic viscera
- Provides attachment for muscles
- Makes up the bony portion of the birth canal in females.
Joints of the Pelvic Girdle
Lumbosacral, Sacroiliac, Symphysis Pubis
False Pelvis
(Aka the greater or major pelvis)
- The bony area between the iliac crests and superior to the pelvic inlet.
- There are no pelvic organs within the false pelvis.
Pelvic Inlet
Can be seen by drawing a line between the sacral promontory posteriorly and the superior border of the symphysis pubis anteriorly
True Pelvis
(aka lesser or minor pelvis)
- Lies between the pelvic inlet and the pelvic outlet.
- Makes up the pelvic cavity
- Contains portions of the gastrointestinal (GI) tract, the urinary tract, and some reproductive organs
- In females, it forms the birth canal.
Pelvic Outlet
Can be seen by drawing a line from the tip of the coccyx to the inferior surface of the pubic symphysis
Differences in the Male and Female Pelvis
- Superior opening into pelvic cavity is more oval in females and more heart-shaped in males
- Pelvic cavity is shorter and less funnel-shaped in females, and sacrum is shorter and less curved
- Iliac walls are not as vertical, and the acetabula (plural of acetabulum) and ischial tuberosities are farther apart in females (makes the area within the female pelvic cavity greater than the longer, funnel-shaped cavity of the male pelvis)
- Pelvic arch is wider and more rounded in females
Pelvic Inlet and Outlet
True and False Pelvis
The bony area between the pelvic inlet and outlet is called…
True Pelvis
The bony area above the pelvic inlet is called…
False Pelvis
Male vs. Female Pelvic Arch
female is bigger than male
Sacroiliac Joint
(aka SI joint)
- Synovial, nonaxial joint between the sacrum and the ilium.
- Describes as a plane joint, but its articular surfaces are very irregular.
- Irregularity helps to lock the two surfaces together.
Function of the Sacroiliac Joint
To transmit weight from the upper body through the vertebral column to the innominate bones
- Designed for great stability and has very little mobility
- Like other synovial joints, its articular surface is lined with hyaline cartilage.
- Synovial membrane lines the nonarticular portions of the joint. It has a fibrous capsule reinforced by ligaments.
Function of the Sacroiliac Joint
To transmit weight from the upper body through the vertebral column to the innominate bones
- Designed for great stability and has very little mobility
- Like other synovial joints, its articular surface is lined with hyaline cartilage.
- Synovial membrane lines the nonarticular portions of the joint. It has a fibrous capsule reinforced by ligaments.
SI Joint Motion
The actual type and amount of movement occurring at the SI joint is the subject of considerable controversy
-It is generally accepted that the motions that do occur at the SI joint are nutation and counternutation
Sacroiliac Joint Motions
Nutation and Countermutation
Nutation
(aka sacral flexion)
- Occurs when the base of the sacrum (on the superior end) moves anteriorly and inferiorly which causes the inferior portion of the sacrum and the coccyx to move posteriorly.
- Pelvic outlet becomes larger and can be visualized by drawing a line from the tip of the coccyx to the bottom surface of the pubic symphysis
Counternutation
(aka sacral extension)
- Base of the sacrum moves posteriorly and superiorly, causing the tip of the coccyx to move anteriorly
- Pelvic inlet becomes larger and can be visualized by drawing a line from the base of the sacrum across to the top of the symphysis pubis
How much motion occurs with nutation and countermutation?
Minimal (and it can occur only in conjunction with other joint motions)
Nutation occurs with…
Trunk flexion or hip extension
Counternutation occurs with…
Trunk extension or hip flexion
Why are movements of nutation and countermutation in conjunction with other joint motions important during childbirth?
When baby moves through pelvic inlet during early stages of labor, the anterior-posterior (A-P) diameter needs to be larger so SI joints are in counternutation
-In later stages of labor, when baby passes through the pelvic outlet, it is important that this A-P diameter has increased and putting the SI joints in nutation increases the A-P diameter.
The two bones of the SI joint are the…
The sacrum and the ilium (the latter of which is the superior portion of the innominate bone)
Sacrum
Wedge-shaped and consists of five fused sacral vertebrae
- Located btw the 2 innominate bones and makes up the posterior border of the bony pelvis
- Anterior surface, often called the pelvic surface, is concave
- Bc it is tilted, the sacrum articulates with the fifth lumbar vertebra at an angle referred to as the lumbosacral angle.
Base of Sacrum
Superior surface of S1
Promontory of Sacrum
Ridge projecting along the anterior edge of the body of S1
Parts of the Sacrum (lateral view)
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Parts of Sacrum (posterior view)
.
Superior Articular Process of the Sacrum
Located posteriorly on the base, it articulates with the inferior articular process of L5
Ala of the Sacrum
Lateral flared wings that are actually fused transverse processes
Ala of the Sacrum
Lateral flared wings that are actually fused transverse processes
Foramina of the Sacrum
Located on the anterior (pelvic) and dorsal surfaces are four pairs of foramina. They serve as the exit for the anterior and posterior divisions of the sacral nerves. The anterior foramina are larger.
Foramina of the Sacrum
Located on the anterior (pelvic) and dorsal surfaces are four pairs of foramina. They serve as the exit for the anterior and posterior divisions of the sacral nerves. The anterior foramina are larger.
Auricular Surface of the Sacrum
Named because its shape is similar to the external ear (auricular is Latin for “earlike”). It is located on the lateral surface of the sacrum and articulates with the ilium. The irregular surface assists in locking the two surfaces together, providing greater stability.
Pelvic Surface of the Sacrum
Concave anterior surface
Ilium
Makes up the superior part of the innominate bone.
Iliac Tuberosity of the Ilium
Large, roughened area between the posterior portion of the iliac crest and the auricular surface. It serves as an attachment for the interosseous ligament.
Iliac Tuberosity of the Ilium
Large, roughened area between the posterior portion of the iliac crest and the auricular surface. It serves as an attachment for the interosseous ligament.
Auricular Surface of the Ilium
Named for its earlike shape, it is the articular surface of the ilium with the sacrum. It is located inferior and anterior to the iliac tuberosity.
Auricular Surface of the Ilium
Named for its earlike shape, it is the articular surface of the ilium with the sacrum. It is located inferior and anterior to the iliac tuberosity.
Iliac Crest of the Ilium
Superior ridge of the ilium, the bony area felt when you place your hands on your hips
Iliac Crest of the Ilium
Superior ridge of the ilium, the bony area felt when you place your hands on your hips
Posterior Superior Iliac Spine of the Ilium
(PSIS) The posterior projection of the iliac crest and serves as an attachment for the posterior sacroiliac ligaments.
Posterior Inferior Iliac Spine of the Ilium
Often abbreviated PIIS, it lies inferior to the PSIS and serves as an attachment for the sacrotuberous ligaments
Posterior Inferior Iliac Spine of the Ilium
Often abbreviated PIIS, it lies inferior to the PSIS and serves as an attachment for the sacrotuberous ligaments
Greater Sciatic Notch of the Ilium
Formed by the ilium superiorly and the ilium and ischium inferiorly
Greater Sciatic Foramen of the Ilium
Formed from the greater sciatic notch by ligamentous attachments. The sacrotuberous ligament forms the posterior medial border of the foramen, and the sacrospinous ligament forms the inferior border. The sciatic nerve passes through this opening.
Parts of the Innominate Bone
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Ligaments of the Pelvis
.
Cross Section of Sacroiliac joints
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Ischial Body of the Ischium
Makes up all of the ischium superior to the tuberosity
Lesser Sciatic Notch of the Ischium
Smaller concavity located on the posterior body between the greater sciatic notch and the ischial tuberosity
Ischial Spine of the Ischium
Located on the posterior body and between the greater sciatic and lesser sciatic notches. It provides attachment for the sacrospinous ligament.
Ischial Tuberosity of the Ischium
The blunt, rough projection on the inferior part of the body. It is a weight-bearing surface when you are sitting.
Sacroiliac Joint
Meant to absorb a great deal of stress while providing great stability, it is heavily endowed with ligaments.
Anterior Sacroiliac Ligament
A broad, flat ligament on the anterior (pelvic) surface connecting the ala and pelvic surface of the sacrum to the auricular surface of the ilium. It holds together the anterior portion of the joint.
Interosseous Sacroiliac Ligament
The deepest, shortest, and strongest of the sacroiliac ligaments. It fills the roughened area immediately above and behind the auricular surfaces and the anterior sacroiliac ligament and it connects the tuberosities of the ilium to the sacrum.
Two Parts of the Posterior Sacroiliac Ligament
Short Posterior Sacroiliac Ligament and Long Posterior Sacroiliac Ligament
Short Posterior Sacroiliac Ligament
Runs more obliquely between the ilium and the upper portion of the sacrum on the dorsal surface. It prevents forward movement of the sacrum.
Long Posterior Sacroiliac Ligament
Runs more vertically between the posterior superior iliac spine and the lower portion of the sacrum. It prevents downward movement of the sacrum.
How many accessory ligaments further reinforce the sacroiliac joint
3 (sacrotuberous ligament, sacrospinous ligament, iliolumbar ligament)
Sacrotuberous Ligament
A very strong, triangular ligament running from between the PSIS and PIIS of the ilium, from the posterior and lateral side of the sacrum inferior to the auricular surface, and from the coccyx. These fibers come together to attach on the ischial tuberosity. It serves as an attachment for the gluteus maximus and prevents forward rotation of the sacrum.