Hip/Pelvis Kinetics Flashcards
Explain the force couple found with an anterior pelvic tilt.
Hip flexors/Lower back extensors, glutes, abdominals, hamstrings. figure 12-27. (anything that create femoral flexion at the hip can create pelvic tilt)
How do the abdominal muscles work during movement of the femur-on-the-pelvis in hip flexion? What happens if the abdominal muscles fail to function properly?
Abdominals stabilize the pelvis by creating a posterior pelvic tilt to counter the anterior pelvic tilt created by the femur. Femur can only move if the pelvis is stabilized. If the stabilization fails to function, there will be anterior pelvic tilt instead of hip flexion.
Explain hip adductors’ function in the frontal plane. Relate adductors’ acceleration of the femur or of the pelvis.
These muscles draw the femur into ADduction across the frontal plane.
Femur on pelvis is open chain, inverse is closed chain.
(In the picture of the girl cross-kicking the ball, the closed chain mvt pulls the hip into hip drop, and the open chain mvt pulls the kicking leg across the body. Pelvis ends in inferior hike.)
What is meant by stating the adductors of the hip provide a “bidrectional torque” in the sagittal plane and what is the significance of this?
The adductors have force vectors for hip flexion and extension. A lot of adductors do flexion in addition to adduction. The adductors can also do extension. It all depends on where the muscle’s line of pull lies in relation to the axis of rotation.
What is the difference in hip internal rotation torque potentials between the positions of anatomical neutral and 90 degrees hip flexion and why?
Piriformis, gemellus bros, etc.–these are muscles dedicated to external rotation only. There is no muscle dedicated to internal rotation of the femur. Tensor fascia lata is the muscle that comes closest to internal rotation.
At 90 degrees of flexion, the line of pull on the adductors is 100% dedicated to internal rotation. Torque potential is much higher at 90.
What is the important function of the hip internal rotators during the stance phase of gait?
The muscles that have internal rotator potential will pull the pelvis forward, creating rotation over the fixed femur during stance phase. Pelvis moves on femur (closed chain). (left forward pelvic rotation = right internal rotation.)
Explain the force couple found with a posterior pelvic tilt.
**(Hip extensors) Gluteus maximus, hamstrings, and rectus abdominus, external oblique muscles (abdominal muscles) work together in different planes to create posterior tilt.
During a forward lean, which muscles maintain the static position at 60 degrees? Why or how?
Hamstrings have a significant stake in controlling the ischial tuberosity. Hamstring moment arm gets longer as the pelvis leans forward at the hip. The ischial tuberostiy moves posterior/superior when the pelvis tilts forward. Torque potential of hamstring increases as the moment arm increases.
Describe the hip abductor mechanism in controlling frontal plane stability of the pelvis during the unilateral limb stance phase of gait (standing on one leg phase).
short answer: Provides a little bit of hip hike on the other side of the pelvis to keep the hips level. The muscles carry a lot of body weight for such a small movement.
long answer: The hip ABductors are resisting gravity to keep the torso and opposite leg from falling over. The ABductor hikes the pelvis just a little bit to defeat gravity. The abductors have a small moment arm compared to the moment arm of the body weight and gravity. So there has to be a large contraction in order to accommodate the difference in moment arms and body weight.
In which condition does the greatest hip joint compression force occur, symmetrical bilateral stance or unilateral stance? Why and what are the contributing forces?
Unilateral–ABductors create a compression force. Body weight of trunk and opposite leg are counterbalanced by the contraction of the hip ABductor. This contraction becomes a compression force that pushes the pelvis against the acetabulum. The compression force creates the Joint Reaction Force that pushes from the ground up to react to the Hip ABductor Force.
Bilateral–weight distribution is equal on both hips (trunk, head, neck, arms), hip ABductors are on but not working as hard as if they were levitating half the body.
Finally, what action might the hip external rotators have functioning at a weight bearing hip in a closed chain situation?
As the right hip externally rotates, the left pelvis will do a left backward rotation moving the pelvis on the femur.
Describe how using a crutch helps change the dynamics of joint compression force.
If one is using a crutch, put the crutch on the opposite side of the hurt leg. The crutch moves in conjunction with the painful leg. The crutch absorbs some of the weight and reduces body weight moment arm. Now there is a long moment arm from the hand to the working hip. Dramatically decreases the amount of strength required by the painful hip.
