Pelvis Flashcards
Osteology of Pelvis Structures
Osteoligamentous ring designed for stability
The bones of the pelvic girdle consist of
2 innominate bones Ilium Ischium Pubis And the Sacrum dorsally
Pelvis articulates with
both the axial and appendicular skeleton
With 5th vertebrae and with 2 femurs at hip joint
5th lumbar vertebrae Body Height Ingerior facet orientation Transverse processes Spinous process
Body - largest and heaviest
Height - great discrepency btw ant and post
Ingerior facet orientation - frontal plane
Transverse processes - shortest, project upward, posterolaterally
Spinous process - smallest
Sacrum
Ant =
POst =
Anterior = concave Posterior = convex
Sacral Hiatus
Access to epidural space for caudal epidural blocks
L5-S1 Junction
High degree of variation and malformation (most common sacralization or lumbarization)
Sacrilzation
L5 is ossified with the sacrum
Lumbarization
Separation of sacrum at S1
Any shear force in LS joint is resisted by
Superior articular process
Spondylolysis - what kind of foce
tensile
Innominate Bones
Divided in 3 parts into acetabulum
Anterior superior = ilium
Anterior Inferior = pubis
Posterior inferior = ischium
Complete ossification of innominate by
20-25 years
Supracristal Plane
The transverse plane at the highest point of the iliac crests
Space btw L4 and L5
Used for assessing the height of the iliac crests
Can also be used for testing leg length discrepancy
Leg length discrepency - 1 method
ASIS to medial malleolus
Gender Diff in Pelvis - Pubic arch angle
50-60 M
90 F
Gender diff in pelvis - Pelvis height
Longer M
Shorter F
Gender diff in pelvis - Sacrum
Longer/Narrower M
Shorter/Wider F
Gender diff in pelvis - Sacral Base Length
> 1/3 body M
Gender diff in pelvis - Acetabular Distance
Smaller M
Greater F
Gender diff in pelvis - ASIS distance
Smaller M
Greater F
Pelvic Inlet angle
50-60 degrees
Pelvic Outlet angle
15 degrees
Super-incumbent weight at sacrum
Head, Arms, and Trunk (HAT)
No matter sitting or standing, weight is at the SI joint
Joints of osteoligamentous ring
2 SI joints (immovable synovial) Sacrum (modified vertebral column) Pubic symphysis (secondary cartilaginous joint)
SI Joint - Joint surfaces
Internal surface of the ilium - behind iliac fossa, auricular sacral surface
SI Joint - Inner surface of ilium
2 parts - upper tuberosity, lower auricular surface
SI Joint - Tuberosity
Rough, for fibers of interosseous sacroiliac ligament
SI Joint - Auricular Suface
Broad synovial joints btw the sacrum and ilium
SI joint auricular surfaces - Form and Force Closure
These surfaces have irrefular elevations and depressions, which result in a partial interlocking of the bones
THe strong articular capsule is attached close to the articulating surfaces of the sacrum and ilium
Sacrum is
suspended btw iliac bones
held together by interosseous and posterior sarcoiliac ligamnets
Strongest ligaments in the body
Ventral SI ligament
thin, wide sheet of transverse fibers anterior and inferior aspects of the SI joint
Replacement of most or all of these fibers by bone often begins after 50 years of age
Dorsal SI ligament
Strong, short transverse and long vertical fibers joining the ilium and sacrum
The long fibers blend with the sacrotuberous ligament
Interosseous Ligament
Massive, very strong ligament unites the iliac and sacral tuberosities
Consists of short, strong bundles of fibers that blend with and are supported by the thick firm posterior sacroiliac ligaments
SI joint movement - SI joint is supported by a
ligamentous viscoelastic structure that was built to stretch small amounts
When you walk, short duration forces being placed across it by your foot hitting the ground and the bending of the spine cause it to stretch and store energy
This energy is released by swinging your leg forward
However - sitting causes some lengthening and stretching of the ligamentous structures
SI joint motion
Symmetrical
Assymetrical
Lumbopelvic
Symmetrical SI joint motion
Sacrum in relation to innominates (both)
Nutation and counternutation
Asymmetrical SI joint motion
Motion of one innominate relative to the other
Sacral or pelvic torsion
Movement at the pubic symphysis - greater with pregnancy and delivery
Lumbopelvic SI joint motion
Lumbar spine and sacrum with the innominates relative to the femurs (hip joint motion)
Anterior Nutation
Sacral on Iliac
Posterior Nutation
Ilium on Sacral
Counter Nutation - Anterior
Ilium on Sacral
Counter nutation - posterior
Sacral on ilium
Nutation icnreases
the compression and shear forces at SI joint (stablity
Full nutation of SI joint
in close packed position
Pelvic Structure at SI joint
Sacrum is wider ant than post
Sacrum behaves as reverse keystone tending to sink into pelvis
POst ligaments become taut and draw iliac bones closer to each other then interlock the iliac bones with the sacrum
Rotation tendencies of pelvis due to superincumban weight - Nutation
Sacrum - Forward rotation at S1
Resisted by interosseous, dorsal sacroiliac and iliolumbar ligaments
Rotation tendencies of pelvis due to superincumbent weight - Lumbopelvic
Os-Coxae = backward rotation at hip
Resisted by sacrotuberous and sacrospinous ligaments
Forces at SI joint during one leg stance
Wight, GRF, JRF, and muscle forces and ligaments will determine the 3D motion btw the bones of the SI joint
A lot of the forces in this joint and support of it experience a lot of tension on a consist basis
