Pelvic Girdle Movement in Labour

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Questions and Answers

How many degrees of forward flexion does the sacrum undergo initially?

30°

60° (correct)

90°

45°

What happens to the sacrum after 60° of forward flexion?

It continues to rotate anteriorly

It begins to counternutate (correct)

It stops moving

It rotates posteriorly

What is the proportion of body weight transmitted to each femoral head?

Half of the body weight (correct)

One-third of the body weight

Two-thirds of the body weight

One-quarter of the body weight

What is the direction of the gravitational torques on the right and left hips?

In opposite directions Signup and view all the answers

What happens when the adductors and abductors contract simultaneously and bilaterally?

The pelvis is stabilized symmetrically Signup and view all the answers

What happens when the abductors predominate on one side and the adductors on the other side?

The pelvis shifts laterally towards the side of adductor muscle synergy predominance Signup and view all the answers

What is the role of active muscles in maintaining pelvic equilibrium in bilateral stance?

They are not necessary to maintain equilibrium Signup and view all the answers

What is transmitted through the sacroiliac joints during bilateral stance?

The superincumbent body weight Signup and view all the answers

What happens to the pelvis when the hips are extended?

It tilts anteriorly Signup and view all the answers

What is the effect of hip flexion on the pelvic inlet?

It decreases the anteroposterior diameter Signup and view all the answers

What occurs when the hips are extended, relative to the fixed sacrum?

Counter nutation Signup and view all the answers

During which stage of labour is the hip extension position beneficial?

Early stage Signup and view all the answers

What is the result of forward flexion of the trunk on the sacroiliac joints?

It increases stress Signup and view all the answers

What occurs to the ilium and pelvic girdle during forward flexion of the trunk?

It rotates anteriorly Signup and view all the answers

What is the effect of hip flexion on the pelvic outlet?

It increases the diameter Signup and view all the answers

What happens to the pelvis when rising from supine lying to sitting?

It tilts anteriorly Signup and view all the answers

What happens when the right abductor torque equals the left adductor torque?

Balance is restored Signup and view all the answers

What is the function of the countertorque during unilateral stance?

To maintain the single-limb support position Signup and view all the answers

Why does the pelvis shift during unilateral stance?

Due to the weight of the non-weight bearing limb Signup and view all the answers

What is the primary function of the hip abductor muscles during walking?

To stabilize the pelvis during unilateral stance Signup and view all the answers

What is the consequence of hip abductor weakness during unilateral stance?

The person leans to the same side Signup and view all the answers

What is the name of the sign that indicates weakened hip abductors?

Trendelenburg sign Signup and view all the answers

What percentage of compressive forces at the hip is attributed to the hip abductor muscles?

Most of the compressive forces Signup and view all the answers

When does the force of HATLL create an adduction torque around the supporting hip joint?

During unilateral stance Signup and view all the answers

Study Notes

Sacral Motion and Forward Flexion

Sacrum nutation occurs up to approximately 60° of forward flexion before posterior structures become tight.
After this point, the innominates rotate anteriorly while the sacrum transitions into counternutation.

Bilateral Stance Mechanics

Body weight is transmitted through sacroiliac joints to the femoral heads, with each head receiving roughly half of the body weight, approximating 2/3 of a normally proportioned body weight.
Gravitational torques act in opposing directions on the hips, balancing each other and maintaining pelvic equilibrium without active muscle assistance.

Muscle Stability in Bilateral Stance

Balanced contraction of adductor and abductor muscles stabilizes the pelvis symmetrically.
If one muscle group predominates, the pelvis shifts laterally towards the side of greater muscular dominance.

Pelvic Girdle Positioning

Hip extension leads to anterior pelvic tilt due to psoas muscle pull, shortening the distance between the sacral apex and ischial tuberosity, promoting counter nutation and enlarging the pelvic inlet.
Hip flexion results in posterior pelvic tilt from hamstring pull, decreasing the anteroposterior diameter of the pelvic inlet while increasing the pelvic outlet dimensions, aiding fetal delivery during labor.

Forward Flexion Effects

Forward trunk flexion exerts stress on sacroiliac, lumbar, and lumbosacral joints, causing anterior rotation of the ilium and pelvic girdle on the femoral heads.
Transitioning from supine to sitting involves similar rotational dynamics, necessitating muscle torque balance to prevent lateral leaning.

Unilateral Stance Dynamics

In unilateral stance, full body weight shifts to the supporting hip joint, alongside the weight of the hanging non-weight-bearing limb, inducing an adduction torque.
Counteracting this torque requires an abduction moment of equal magnitude to maintain stability during single-limb support.

Muscle Stability in Unilateral Stance

Hip abductor muscles are crucial for stability while walking, producing most of the compressive forces at the hip joint.
A person with weak hip abductors demonstrates a Trendelenburg gait, characterized by pelvic drop on the side of the lifted lower limb and compensatory trunk lean towards the weaker side during single-leg support.

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Description

Learn about the effects of hip extension on the joints of the pelvic girdle, including the movement of the sacrum and iliac bone, and its relation to the early stages of labour. Understand how the position of the hips affects the pelvic inlet and the descent of the fetus. Test your knowledge of pelvic girdle anatomy and its role in childbirth.