Hip Biomechanics Flashcards
ROM degrees of freedom
Ball & socket
6 DOF
Acetabular orientation
20 degrees anteriorly from the frontal plane
40 degrees inferiorly from the transverse plane
what happens to the acetabular lunate during stance phase?
articulating surface
the lunate surface flattens slightly as the acetabular notch widens and increases contact area and reduces peak pressure
non articular surface: acetabular fossa
what does it contain
depression deep within floor of acetabulum
contains:
- teres ligament
- fat synovial membrane
- blood vessels
acetabular labrum
improves congruencey
deepens the socket and securely grips the periphery of the femoral head
plane of center edge angle
-frontal plane
average angle of Center edge angle
22-42 degrees
function of center edge angle
- provide lateral stability
- prevent superior dislocation
- increases with age (why children are most prone to hip dislocation)
angle of inclination
125 degrees
inclination angle at birth
140-150 degrees
- decreases over time because of the loading across the femoral neck during walking
coxa varus
<125
hip bends inward
coxa valgus
> 125
hip bends outward
function of angle of torsion
transverse plane
- plays a role in hip stability
- possible cause of IR or ER
- prevent threatening congruence during torsion
reason for angle of torsion
femoral condyles align themselves so the knee joint axis lies in frontal plane
trabecular intersection areas represent
locations of cortical bone strength
trabecular voids represent
locations of cortical bone weakness
hip joint capsule
- joint stability
- thicker where greater stress occurs including periphery of acetabulum
internal capsular ligaments
transverse acetabular
ligamentum teres
transverse acetebular
forms tunnel for blood vessels and nerves to enter and exit hip joint
ligamentum teres is under tension when
not major stabilizer but under tension in ADD/ flexion
External capsular ligaments
illiofemoral
pubofemoral
ischiofemoral
illiofemoral ligament
- strongest ligament at the hip
- taut during extension
- limits anterior displacement of femur
pubofemoral ligament
-prevents anterior displacement of femur
ischiofemoral
prevents posterior displacement of femur
tight in extension
majority of muscles at the hip joint are
unipennate biarticular , and bipennate
(1) provides good ROM with efficiency of movement
(2) provide strength
Hip Flexors
- illiopsoas
- rectus femoris
- TFL
- Sartorius
rectus femoris
most effective hip flexor when knee is flexed
TFL
Flexion, ABD, MR
Sartorius
- longest muscle in body
- flexion & ABD (depending on position of the limb)
Hip Extensors
glute max
hamstrings
glute max
primary used with hip in flexion (stair climbing and cycling)
moment arm of glute max
shorter than other extensors –> this muscle needs to be strong to generate force
- max force in hip in neutral
hamstrings
extend hip with or without resistance
hip abductors
- gluteus medius
- stabilize pelvis during support phase of ambulation
- single limb support
hip adductors
can produce greater isometric torque than ABD
you can create more force trying to close the legs than opening
secondary function of hip adductors
flexion of hip and knee
Hip LR
Quadratus femoris, piriformis, obturator & gemellus
function of Hip Lateral Rotators
stabilizing role
-outward rotation of femur occurs to accommodate rotation of pelvis during every step
Hip Medial Rotatores
- no muscles have this as primary function
- secondary: anterior glute min, TFL
- does not require a lot of force
Medial Rotator strength is ____ of lateral rotator strength
1/3
function of hip joint
- support head, arms, trunk
- closed kinematic chain
- provide a pathway for the transmission of force between the pelvis and LE
closed packed position of hip joint
full extension, medial rotation and abduction
ligaments taut
loose-packed position
flexion 90 degrees, small abduction, and lateral flexion
ligaments slack
position of greatest risk for dislocation of hip joint
flexed and adducted (figure 4)
mild force along the femoral axis can cause posterior dislocation
factors affecting stability of the hip joint
- atmospheric pressure
- shape of the articulating surface
- labrum acetabular
- direction of the femoral neck
- capsule encircle the femoral neck
- ligaments & periarticular ms
What is pelvic motion at the hip
when weight bearing all hip motions are due to pelvic motion rather than thigh motion
(situations where LR not free to move)
Anterior Pelvic Tilt
ASIS rotates forward & butt rotates posteriorly
sacral angle rotates forward
occurs naturally when extra anterior mass is present
lordosis
Posterior Pelvic Tilt
pubic symphysis up, ASIS back
“tuck” or “squeeze buttocks”
decrease lumbar curve
can occur at both hip joints or in single limb support
Lateral Tilt
one hip joint serves as pivot and opposite iliac crest elevates (hip hiking) or drops (pelvic drop) with respect to pivot point
stand on left leg in single support & right pelvis drops
left hip adduction
Bilateral standing in sagittal plane
LOG falls posterior to hip joint axis (extension) checked by passive tension in the ligaments & joint capsule
Bilateral standing in frontal plane
weight of head , arms and trunk = 2/3 of BW
1/3 for each hip
symmetrical bilateral standing
no muscle activity needed
asymmetrical bilateral standing
simulatenous contraction of the ipsilateral and contralateral ABDuctors and ADDuctors to restore balance
unilateral standing
stance hip carries 5/6 of body weight
4/6 HAT + 1/4 of other LE
importance of joint reaction forces
if the hip joint undergoes osteoarthritic changes leading to pain on weight bearing , the JRF must be reduced to avoid pain
strategies to reduce joint reaction force
- weight loss
- reduction of abductor muscle force
- using the cane ipsilaterally and contralaterally
weight loss (joint reaction force)
reduce 1N of body weight will reduce JRF 3N
reduction of abductor muscle force (JRF)
reduce the moment arm of the gravitational force through lateral leaning of trunk towards the side of pain and weakness
gluteus medius gait
if lateral trunk lean is due to hip abductor weakness
antalgic gait
if lateral trunk lean is due to hip jont pain
using the cane ipsilateral and contralateral
ipsi - provides benefits in energy expenditure by reducing BW by the amount of downward thrust
(lateral trunk lean is more effective)
using the cane contralaterally
relieves the hip joint of 60% of its load in stance
equation of equilibrium
abductor muscle torque + cane torque (latissimus dorsi) = gravitational force
two peak forces
1st (4w) - just after heel strike
2nd (7w) just before toe off (abductor ms)
Hip injury
subjected to 4-7 x body weight during locomotion (high repetition)
what injury is most common in the elderly
femoral neck fractures
other types of hip injury
- strains to surrounding muscles
- contusions -impact force on muscles
