Trendelenburg sign in gluteus medius paralysis. True or False Reasoning out
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Reading File
Answer: TRUE
The Trendelenburg sign is positive (TRUE) in gluteus medius paralysis.
The Anatomy and Biomechanics
The gluteus medius (along with gluteus minimus) is the primary hip abductor. Both muscles:
- Originate from the outer surface of the ilium
- Insert on the greater trochanter of the femur
- Are innervated by the superior gluteal nerve (L4, L5, S1)
During normal single-leg stance (e.g., walking), the gluteus medius on the stance side fires powerfully to stabilize the pelvis - it prevents the opposite (swing) side of the pelvis from dropping.
What Happens in Gluteus Medius Paralysis?
When the gluteus medius is paralyzed or severely weak on one side, it cannot hold up the opposite side of the pelvis during single-leg stance on the affected limb.
Result: The pelvis drops (tilts inferiorly) toward the unaffected/swing side - this is a positive Trendelenburg sign.
As Gray's Anatomy for Students states directly: "Trendelenburg's sign occurs in people with weak or paralyzed abductor muscles (gluteus medius and gluteus minimus) of the hip... When the patient stands on the affected limb, the pelvis severely drops over the swing limb." - Gray's Anatomy for Students, p. 680
The Compensation - Trendelenburg Gait
To prevent the pelvic drop from causing a stumble, the patient compensates by lurching the trunk toward the affected (stance) side. This shifts the body's center of gravity over the stance leg without needing abductor muscle power - it is called the Trendelenburg (or abductor) lurch/gait.
Memory Hook
"The pelvis drops to the OPPOSITE side of the lesion"
- Weak side = stance side = cannot hold the pelvis level
- Pelvis drops = toward the normal/swing side
Causes of a Positive Trendelenburg Sign
| Cause | Mechanism |
|---|---|
| Gluteus medius / minimus paralysis | Direct muscle weakness |
| Superior gluteal nerve damage | Nerve injury (pelvic fracture, surgery) |
| Hip dislocation / DDH | Altered lever arm mechanics |
| Coxa vara | Shortened abductor lever arm |
| Greater trochanter avulsion fracture | Loss of abductor insertion |
| Polio / neuromuscular disease | Lower motor neuron weakness |
Bottom line: The statement is TRUE. Paralysis of the gluteus medius abolishes the hip abductor's stabilizing function, causing the pelvis to drop to the contralateral side during single-leg stance - the hallmark of a positive Trendelenburg sign.
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