Hip Flashcards
Acetabulum
Pubis: 25% of acetabulum anteriorly
Ischium and ilium together: 75% of acetabulum
- Ischium: posteriorly
- Ilium: superiorly
Incomplete rim inferiorly = acetabulum notch, spanned by transverse acetabular ligament
Opening allows us to have a lot of mobility as femoral head rolls/glides around acetabulum
Acetabular Dysplasia
Malformed acetabulum leads to lack of femoral head coverage
Acetabulum not formed properly - instability in joint (surfaces are not big enough)
Altered stresses b/c surface area is congruent or smaller surface area
Acetabular Alignment - Center Edge Angle
Describes orientation of the acetabulum
Fixed angle of acetabulum in frontal plane (orientation of acetabulum in frontal plane)
Measures from hip joint center to rim of acetabulum (measure how much acetabular rims covers femoral head)
Too little coverage - dysplastic hip (dislocate)
Too much coverage can cause pinching and discomfort as head rolls out into abduction (pinching b/w acetabulum and femoral neck)
Looking at superior edge of femoral head and how much coverage acetabulum is giving
<16 degrees - markedly reduced acetabular coverage-dysplasia, increased stress
16-25 - reduced acetabular coverage - possible dysplasia, increased stress
35-40 - normal
> 40 - too much coverage
Acetabular Alignment - Acetabular ante- and retro version
Transverse/horizontal plane
What direction acetabulum face
Anteversion
- Acetabulum faces too far anteriorly (dislocate hip anteriorly)
- Can lead to unstable hip
- Opening up joint
- Ball is going to pop out of socket anteriorly
Retro version
- Acetabulum faces too far posteriorly
- Can lead to over-coverage, impingement b/w acetabulum and femoral head, abnormal stresses
Position can’t be created
Normal - 20 degrees
Anteversion - more than 20 degrees
Retroversion - less than 20 degrees
Labrum
Fibrocartilaginous ring functions to deepened acetabulum b/c it’s not deep enough
Provides stability, but more mobility
Increases contact area
Decreases stress
Labral tears are known source of pain
- Poor vascularization
- Doesn’t head well
Angle of Inclination
Frontal plane angle b/w femoral neck and femoral shaft
Normally 125 degrees
Coxa valga and coxa vara
Coxa Valga
Pathological increase (angle of inclination is more than 125 degrees)
Vertical orientation - moment arm of hip abductors is smaller - less mechanically advantageous - need to work harder
Coxa Vara
Pathological decrease (angle of inclination is less than 125 degrees)
Put more pressure on neck - more bending moment
Suffer from neck fractures
Abductors can function better here - moment arm increases (greater force can be generated, less work needs to be done) - greater mechanical advantage
Angle of Torsion
Femoral torsion describes relative motion (twist) b/w shaft and neck
Line thru femoral neck, condyles, head
Normally, 15 degrees anterior to frontal plane
Independent of acetabulum - occur on femur
Position of neck relative to femur
Excessive Anteversion
Angle of torsion
Increase in torsion - femur sits anteriorly
Less congruency b/w jt surfaces
Neck is more anterior to line from trochanter through femoral head
Individuals turn toes in, so that femoral head can IR and roll backward to increase joint congruency in acetabulum
Can be caused by W sitting in kids
Walk pigeon toes and can’t ER
More than 15 degrees
Retroversion
Angle of torsion
Line projects closely to frontal plane
Less than 15 degrees
Proximal Femur Internal Structure
Large bending moments at femoral neck
Bending moments reinforced by thick cortical bone/organized arrays of cancellous/trabecular bone
Cancellous bone extends from shaft to neck and head in organized arrays
Thick compact bone in cortex of lower femoral neck and in shaft
Capsule
Contributes substantially to stability
Thickened anteriorly/superiorly, thin posteriorly/inferiorly
Femoral neck - intracapsular
Greater/lesser troch - extracapsular
Synovial membrane
Mostly oriented parallel from neck to femur
Blood supply occurs here at the attachment of capsule to bone – vessels carrying blood to femoral neck and head
More likely to get femoral neck fractures b/c there is not a good blood supply to that region (just vessels to that area)
Hip is more likely to dislocate posteriorly b/c capsule is thinner
Ligaments
Reinforce capsule
Limites extreme motion
Iliofemoral, pubofemoral, ischiofemoral
End ROM of hip – defined by ligaments, capsules, muscles
Iliofemoral Ligament
Y ligament
Resists hip extension
Fan shaped, resembles inverted Y
Anterior
Provides stability when hip is extending (femoral head goes anterior)
Pubofemoral Ligament
Anterior
Ischiofemoral Ligament
Posterior
Hip Joint Stability
Achieved due to:
- Bony configuration
- Strong capsule
- Reinforcing ligaments
Most congruent position - 90 degrees hip flex, slight abduction, ER
Close-Packed Position
Full ext, slight IR, abduction
Elongates most of capsule, not the most congruent
Most taut
Open-Packed Position
30 degrees of hip flex, slight abduction, ER
Most space in capsule
Feeling good for patient who is swollen/edema (room for fluid to move)
Can shorten hip flexors and cause contracture