Pelvis and Innominates Flashcards
What 3 bones make up the innominate?
Made up of :
Ilium
Ischium
Pubis
What does the pelvis begin to fuse?
16 years
What are the 3 major joints of the pelvis?
SI
Pubic Symphysis
Acetabulum
Why does SD of the pelvis have far-reaching effects? Why does SD affect the pelvis so much?
Through muscular and fascial connections, the Pelvis directly connects to every other area in the body—torso, upper extremity, axial spine, head, rib cage, lower extremity! Somatic dysfunction here can have far reaching effects.
Conversely, somatic dysfunction distally can have effects on the pelvis.
Why is the pelvis the central hub of the body?
Fascial and muscular connections to the rest of the body
Central role in coupling mechanical forces of the LE with the axial skeleton
Innominates are integral part of creating a stable and mobile pelvic ring
What is structural integrity in the context of the pelvis?
Structural integrity is the ability to maintain structure in the face of a torso and forces of gravity on top of it.
Why does the pelvis allow for mobility?
In order for us to move through our world with a fair amount of ease, the pelvis must also have a certain degree of mobility.
The joints, particularly the SIJ, must be able to move in response to muscle action without losing the structural integrity.
What is the self bracing mechanism of the pelvis?
Attained by form + force closure
Model that allows for efficient locomotion and weight transfer
How is form closure of the pelvis attained?
Form closure via structural anatomy of wedge shaped sacrum
Internal anatomy and shape of bones in the SIJ
How is force closure of the pelvis attained?
Force closure requires horizontal, lateral compressive force and friction to withstand vertical load
- from mm supporting the pelvis
What kind of joint is the SIJ?
The SIJ is a synovial joint between the auricular surfaces ofthe sacrum bone and the two ilium bones.
The auricular surfaces are covered in hyaline cartilage and are broader above and narrower below.
The SIJ is also a true diarthrodial joint, as it has a joint space, filled with synovial fluid between the matching articulating surface and a fibrous capsule. However it is different to other diarthrodial joint as it has fibrocartilage and hyaline cartilageon the auricular surfaces
What is the main role of the SIJ?
2]The SIJmain roles are to provide stability and offset the load of the trunk to the lower limbs
How is movement done at the SIJ? About how much movement is there? On what plane does movement happen?
There is very limited movement at the SIJ, with some literature suggesting as little as4 degrees
The two main movements occur when the sacrum moves relative to theiliac bones in the sagittalplane
What is nutation?
Nutationdescibes when the sacrum is rotated forwards relative to the iliac bones
What is counternutation?
Counternutationdescribes when the sacrum is rotated backwards relative to the iliac bones
Which is more stable, nutation or counternutation?
Nutation can be regarded as anticipation for joint loading, as it is a more stabile than counternutation
What happens during nutation to increase stability? During what activities does this occur?
During nutation the posterior parts of the iliac bones are compressed into the “keystone-like” shape, and the joint is in the lockedand close packed position.
This normally occurs during increased load bearing situations e.g. standing and sitting, to increase stability
What bony features increase form closure? How does the SIJ contribute? The sacrum?
The sacrum and the ilium eachhave one flat surfaceandoneridged surfacewhich interlock together, promoting stability.The symmetrical grooves and ridges allow the highest coefficient of friction of any diarthrodial joint and protect the joint against shearing.
The position of the bones in the SIJ creates a “keystone-like” shape which adds to the stability in the pelvic ring. This “keystone” shape is created, as the sacrum has a wider side superiorly, which allows the sacrum to be “wedged” in between the ilium
Why is force closure needed?
Although form closure provides stability to the SIJ, for mobility to occur further joint compression and stabilisation is required to withstand a vertical load.
Force closure is the term used to describe the other forces acting across the joint to create stability.
What specific features of structures allow them to create force closure?
This force is generated by structures with a fibre direction perpendicular to the sacroiliac joint and is adjustable according to the loading situation.
Muscles, ligaments and the thoracolumbar fascia all contribute to force closure.
When is force closure important?
. Force closure is particularly important during activities such as walking when unilateral loading of the legs creates shear forces
How does force closure affect form closure?
Force closure creates greater friction and therefore increased form closure and what is called “self-bracing” or “self-locking” of the joint.
According toWillard et al.force closure reduces the joint’s ‘neutral zone’ therebyfacilitating stabilisation.
Other than form and force closure, what else provides stability to the pelvis?
As the ilium and sacrum only meet for approximately a third of the surfaces, the rest of the stability between the bones is provided by the ligaments
What specific structures contribute to force closure?
Sacrotuberous and sacrospinous ligaments
Multifidus Latissimus dorsi Piriformis Gluteus maximus Biceps femoris
