203 Hip And Thigh Muscles

Question 1

Explain the Trendelenburg sign, importance, muscles invovled, causes , implication of positive sign

Trendelenburg Sign & Hip Abductor Function – Flashcard Questions
1. What is the purpose of the Trendelenburg test?
2. Which muscles are primarily responsible for hip abduction?
3. Which nerve innervates the gluteus medius and minimus muscles?
4. What is a positive Trendelenburg sign?
5. What causes the pelvis to drop on the unsupported side during the Trendelenburg test?
6. Why does weakness of the gluteus medius and minimus cause pelvic tilt?
7. How does the body compensate for a weak abductor during walking?
8. What is a compensated Trendelenburg gait?
9. Why does the trunk lean toward the affected side in compensated Trendelenburg gait?
10. What happens to the center of gravity when the trunk leans toward the affected side?
11. How does the Trendelenburg sign help identify superior gluteal nerve injury?
12. What spinal nerve roots contribute to the superior gluteal nerve?
13. During single-leg stance, how do hip abductors stabilize the pelvis?
14. What other conditions besides nerve injury can cause a Trendelenburg gait?
15. How would a patient with bilateral abductor weakness present when walking?
16. What is the difference between Trendelenburg gait and antalgic gait due to pain?
17. What anatomical side is being tested when a patient stands on their right leg?
18. In a positive Trendelenburg test, which side of the pelvis drops?
19. Why doesn’t the pelvis drop when hip abductors are functioning normally?
20. What is the function of the gluteus minimus compared to the gluteus medius?

Answer 1

Trendelenburg or waddling gait.
Trendelenburg sign is used to test the integrity of the hip abductor muscles. It occurs due to disruption of these muscles.
The two main muscles for hip abduction are gluteus minimus and medius. Medius is the main hip abductor. Both are innervated by superior gluteal nerve
Injury to L3-L5 nerve root or avulsion of the tendons of these muscles.
Abductor muscles keep the pelvis level during single stance or when patient stands on one leg. If you stand on both legs, each leg carries half the body weight.
When you’re standing on one leg, the supporting leg takes the entire load.

If the hip abductors connected to the supporting leg (leg touching the ground) are intact, the pelvis will remain level and the trunk will not lean towards any side.

ABDUCTOR
INJURY CAUSES TILT OF PELVIS
AWAY FROM AFFECTED
SIDE
If the abductor muscles of the supporting leg are injured or affected, then the patient will show the Trendelenburg sign.

When checking the integrity of the right side hip abductor muscles, stand behind the patient and ask the patient to stand on one leg. If the hip abductors connected to the supporting leg (leg touching the ground) are intact, the pelvis will remain level and the trunk will not lean towards any side.
Contra lateral hemi pelvis hip drop
Pelvis leans towards unaffected side but trunk leans towards affected side.

The trunk helps in stabilizing the pelvis and maintaining the center of gravity by leaning towards the affected side of the pelvis.

What happens when the gluteus medius/minimus muscles are weak?
• These muscles normally hold your pelvis level when you stand on one leg.
• When you lift one leg (like during walking), the muscles on the standing leg side contract to keep your pelvis from dropping on the side where the leg is lifted.

If those muscles are weak or not working:
• When you stand on that leg, the pelvis drops down on the opposite side (the side where the foot is lifted).
• This is because the weak muscles can’t hold the pelvis level.

What does this mean for walking?
• The person may develop a Trendelenburg gait, which looks like this:
• When they stand on the weak leg, they lean their upper body towards the weak side.
• This leaning helps reduce the force needed by the weak muscles to hold the pelvis steady.
• But it causes an abnormal walking pattern, and sometimes discomfort.

Why does the patient lean toward the weak side?
• Think of it like trying to balance a heavy load on one side.
• By leaning toward the weak side, they reduce the load or demand on the weak muscles, making it easier to stand or walk without falling.

Great question — and yes, it can seem counterintuitive at first. Let’s clear it up with anatomy, mechanics, and clinical reasoning behind the Trendelenburg sign:

📌 Why does the pelvis tilt down to the unaffected side in a positive Trendelenburg test?

Because the affected side’s muscles (gluteus medius & minimus) are too weak to hold the pelvis level when you’re standing on that leg.

🔍 Imagine this:

Let’s say the right gluteus medius and minimus are weak.

What happens during the Trendelenburg test:
1. The patient is asked to stand on the right leg (affected side).
2. The left leg (unaffected side) is lifted off the ground.
3. Normally, the right gluteus medius/minimus contract to keep the pelvis level.
4. But if they’re weak → they fail to stabilize the pelvis → so the pelvis tilts down on the left side (the unaffected, lifted side).
• Because there’s no muscular support to hold it up on the right side.

🟡 Result: Pelvis tilts downward on the unaffected (lifted) side — that’s the positive Trendelenburg sign.

🧍‍♂️ What about the lean?

When walking, patients will compensate:
• They lean toward the affected (weak) side during stance phase — this is called a compensated Trendelenburg gait.
• Why?
• Leaning toward the weak side moves the center of gravity closer to the hip joint.
• This reduces the torque and demand on the weakened muscles, helping prevent pelvic drop.

🔁 So, to clarify:

Situation What happens
Trendelenburg test Pelvis drops on the unaffected side when standing on the affected side
Gait (walking) Person leans toward affected side to compensate for weak hip abductors
Pain (e.g. arthritis) Patient may lean toward affected side due to pain, but this is a different mechanism from muscle weakness

Let me know if you’d like this illustrated or summarized in a diagram-style breakdown!

Here are the answers to the Trendelenburg and gluteal region flashcard questions for OSCE prep:

🦴 Trendelenburg Sign & Hip Abductor Function – Flashcard Answers
1. What is the purpose of the Trendelenburg test?
→ To assess the strength and integrity of the hip abductor muscles (mainly gluteus medius and minimus) on the weight-bearing leg.
2. Which muscles are primarily responsible for hip abduction?
→ Gluteus medius and gluteus minimus.
3. Which nerve innervates the gluteus medius and minimus muscles?
→ Superior gluteal nerve (L4, L5, S1).
4. What is a positive Trendelenburg sign?
→ Pelvis drops on the side of the lifted (unsupported) leg when the patient stands on the affected (supporting) leg.
5. What causes the pelvis to drop on the unsupported side during the Trendelenburg test?
→ Weakness or paralysis of the hip abductors on the supporting leg.
6. Why does weakness of the gluteus medius and minimus cause pelvic tilt?
→ These muscles normally contract to stabilize the pelvis. If they’re weak, they can’t counterbalance the weight of the opposite side.
7. How does the body compensate for a weak abductor during walking?
→ The patient leans their trunk toward the weak (affected) side to shift the center of gravity and reduce the demand on the abductors.
8. What is a compensated Trendelenburg gait?
→ A gait where the patient leans the torso toward the affected side to reduce pelvic drop caused by weak abductors.
9. Why does the trunk lean toward the affected side in compensated Trendelenburg gait?
→ To bring the center of gravity closer to the hip joint and reduce the load on the weak muscles.
10. What happens to the center of gravity when the trunk leans toward the affected side?
→ It moves closer to the hip joint, decreasing the lever arm and muscular effort needed.
11. How does the Trendelenburg sign help identify superior gluteal nerve injury?
→ Injury to this nerve weakens gluteus medius/minimus, leading to a positive Trendelenburg sign.
12. What spinal nerve roots contribute to the superior gluteal nerve?
→ L4, L5, and S1.
13. During single-leg stance, how do hip abductors stabilize the pelvis?
→ By contracting to prevent the pelvis from tilting downward on the unsupported side.
14. What other conditions besides nerve injury can cause a Trendelenburg gait?
→ Muscle tears, muscular dystrophy, hip joint dislocation, or avulsion of the gluteal tendons.
15. How would a patient with bilateral abductor weakness present when walking?
→ Waddling gait — alternating pelvic drops on each side, often seen in muscular dystrophy.
16. What is the difference between Trendelenburg gait and antalgic gait due to pain?
→ Trendelenburg gait is due to muscle weakness; antalgic gait is due to pain avoidance (limping).
17. What anatomical side is being tested when a patient stands on their right leg?
→ The right side — the supporting leg’s abductors are being tested.
18. In a positive Trendelenburg test, which side of the pelvis drops?
→ The side opposite to the one standing (the unsupported leg side).
19. Why doesn’t the pelvis drop when hip abductors are functioning normally?
→ The gluteus medius/minimus contract to hold the pelvis level during single-leg stance.
20. What is the function of the gluteus minimus compared to the gluteus medius?
→ Both abduct the thigh and stabilize the pelvis; gluteus minimus also assists in medial rotation.

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