Pelvis and Hip Biomechanics - part 1

what 3 bones compose the pelvis

right hemipelvis, left hemipelvis, sacrum

the pelvis is extremely

stable due to bony and ligamentous support

the pelvis is often referred to as a

ring

the pelvis is built for what type of load

axial due to gravitational and reactive forces

what helps to disperse load through the bony structures of the pelvis

musculature and ligaments

what is the keystone of the pelvis

the sacrum

without the sacrum what would happen to the stability of the pelvis

it would decrease

what does the sacrum connect

the two hemipelvises

what does the sacrum do

help transmit load through the whole ring of the pelvis

where does SI pain often come from

piriformis and butt ladder muscles, all glutes

DOF of the pelvic ring

6 but very minimal (maybeeee 8 degrees)

is the SI joint easy to palpate

nope there is less motion than we can really see or measure

what is the center edge angle (wiberg) of the acetabulum

the middle of the femoral head to the edge of the pelvis which is 30-40 degrees and acts as a protective shelf

with a smaller wiberg / center edge angle what can happen

there is less head coverage so increased risk for dislocation and DJD

if the wiberg / center edge angle is larger than 35 degrees what can happen

there is too much coverage so there is an increase risk for Femoracetabular impingement and DJD

acetabular anteversion indicates

coverage of the femoral head which is typically around 20 degrees

acetabular anteversion in negatively impacted by

anterior pelvic tilt

increased or decreased anteversion in the acetabulum can lead to

DJD or FAI due to abdonormal stress

what is the articular surface of the acetabulum

lunate surface superior and anterior that is maximized articular cartilage compression. The non-articular surface contains fat.

what does the labrum of the hip do

restrains the head by gripping it, creates a vacuum tight seal and powerful suction, air seal resists distraction and fluid seal maintains lubrication of the joint and fluid cushion

rate and the amount of loading of the femoral head are

inversely proportional to the amount of deformation

acetabular labrum has maximal load bearing and head restraint in

flexion

injury / effusion to the labrum results in

increased pressure, inhibits hip extensors especially glute max, reduces ROM, and increases flexor contracture risk

with open pack position there is

the lowest pressure and maximal comfort

what is open packed position of the hip

30-45 degrees of flexion, 15-20 degrees of abduction, 10-15 degrees of ER

what should you do if there is injury / effusion to the larbum

work to activate glute max, avoid letting Hamstring substitute completely, lengthen the anterior capsule and hip flexors, avoid lumbar hyperextension

what is acetabular load with initial contact

low

what is acetabular load when the foot is flat in midstance

maximum

how does the acetabulum surface area increase in midstance

acetabular notch widens, lunate surface compresses, viscoelastic during loading

what is the weight bearing of the acetabulum during heel off

progressive reduction

what is the weight bearing of the acetabulum during swing phase of gait

minimal loading due to intra-articular pressure

the femoral head is covered in

articular cartilage

what is the viscoelastic loading of the femoral head

continuous. loading is good due to wolffs law

angles of the femoral neck

torsion (anteversion and retroversion) and inclination angles (coxa valga and coxa vara)

how do we maintain the health of articular catilgae

via regular intermittent loading

what is the normal torsion angle of the femur

15 degrees

what is an excessive antiversion angle of the femur

35 degrees

what is a retroversion angle of the femur

35 degrees

torsion angle stability from most to least

retroversion, normal, excessive antiversion

with excessive femoral anteversion there is

a reduced hip abduction moment arm

what is the inclination angle of the femur

the angle between the femoral neck and shaft

normal angle of inclination

125

coxa vara angle of inclincation

105

coxa valga angle of inclination

140

newborn angle of inclination

165-170

severe malalignment of the angle of inclination may lead to

dislocation or stress induced degeneration of the joint

what is does a positive coxa vara lead to

increased moment arm for hip abductor force and alignment may improve joint stability

what does a negative coxa vara lead to

increased bending moment arm which increases shear force across the femoral neck and decreased functional length of hip abductor muscles

what does a positive coxa valga angle lead to

decreased bending moment arm, decreased shear force across the femoral neck

what does a negative coxa valga angle lead to

decreased moment arm for hip abductor force and alignment may favor joint dislocation

in toeing is common with

excessive anteversion which aligns optimal surface area contact and moment arm force for musculature attachments

why does the fat pad of the acetabulum generate pain

it is highly innervated and generates pain especially in the closed pack position

what is closed pack position of the hip

extension, adduction, IR

with end range hip flexion / knee extended what is taut

hamstrings

with end range hip flexion / knee flexed what is taut

glute max, posterior and inferior capsule

with end range hip extension with knee extended what is taunt

primarily iliofemoral ligament but also anterior capsule, some fibers of the pubofemoral and ischiofemoral ligaments, and iliopsoas muscle

with end range hip extension and knee flexed what is taut

rectus femoris

with end range hip abduction what is taut

pubofemoral ligament and adductor muscles

with end range hip adduction what is taut

IT band, abductor muscles such as TFL and glute med

with end range hip IR what is taut

ischiofemoral ligament, ER muscles such as piriformis and glute max

what end range hip ER what is taut

iliofemoral and pubofemoral ligaments, IR muscles such as the TFL and glute min

internal moments are produced by

non-contractile structures and contractile structures in passive restraint when active

tension of the iliofemoral / ligament of bigelow is due to what posture

anterior pelvic translation, posterior pelvic tilt, center of mass posterior to hip which loads anteriorly and increases capsular load

functional assist loading of the iliofemoral / y ligament of bigelow

significant LE weakness, COM posterior to hip, creates stability for functional tasks, tension is used to propel the LE forward

what does a posterior pelvic tilt do

shift the acetabular load anteriorly, increase loading on the edge of the acetabulum, reduce coverage of the anterior femoral head, reduce stability and increase labral / capsular loads

what happens when the COM is posterior to the hip

creates higher external extension moments, higher internal flexion moments, and higher loads resisting hip extension and anterior capsule / hip flexors

what is the cornerstone between the LE and UE

the hip and pelvis

what are soft tissue barriers to closed packed position

iliofemoral ligament, ischiofemoral ligament, and pubofemoral ligament

what is the pretzel effect of the pelvis

a fracture at one point will lead to a fracture at another point which is not good because it holds your organs