SN4
SHORT NOTE
5M
★ High-yield
Describe the Trendelenburg sign with its mechanism and causes.
Definition
The Trendelenburg sign is a test of the abductor mechanism of the hip, chiefly gluteus medius and minimus.
The Normal Mechanism
- Nerve supply — the superior gluteal nerve (L4, L5, S1)
- The abductors act on the standing side to keep the opposite side of the pelvis up — this is the crux of the test
The Positive Sign
- The patient stands on the affected leg
- The pelvis droops on the opposite (unsupported, normal) side
- The trunk lurches toward the affected side to compensate
- Bilateral involvement produces a waddling gait
Causes of a Positive Trendelenburg Sign
| Category | Causes |
|---|---|
| Weak abductors | Superior gluteal nerve injury (badly placed intramuscular injection); poliomyelitis; muscular dystrophy |
| Loss of the fulcrum | Dislocation of the hip (congenital or acquired); coxa vara; ununited fracture of the neck of femur |
| Shortened lever arm | Excision of the femoral head; slipped upper femoral epiphysis |
| Painful hip | Any painful condition — the patient will not contract the abductors (a false positive) |
The Gluteal Muscles
| Muscle | Nerve | Chief action |
|---|---|---|
| Gluteus maximus | Inferior gluteal (L5, S1, S2) | Extension and lateral rotation; chiefly used in climbing and rising from sitting, not in ordinary walking |
| Gluteus medius | Superior gluteal (L4, L5, S1) | Abduction; steadies the pelvis in walking |
| Gluteus minimus | Superior gluteal | Abduction and medial rotation |
| Tensor fasciae latae | Superior gluteal | Tenses the iliotibial tract; assists abduction |
Applied Aspects
- Intramuscular injection into the upper outer quadrant is essential — a misplaced injection may damage the superior gluteal nerve (Trendelenburg gait) or the sciatic nerve (foot drop). Injection palsy remains a preventable cause of childhood disability in India
- Developmental dysplasia of the hip presents in a walking child with a positive sign and a waddling gait; earlier it is detected by the Ortolani and Barlow tests
- Total hip replacement must restore the offset and abductor lever arm, or a persistent limp results
- Distinguish from an antalgic gait — in that the stance phase is shortened on the painful side, whereas in a Trendelenburg gait the trunk lurches
- Gluteus maximus is a muscle of power, not of ordinary walking — which is why its paralysis is far less disabling than that of gluteus medius
All questions in Lower Limb
- Q1Describe the boundaries and contents of the femoral triangle. Add a note on the femoral sheath and the femoral canal. ★
- Q2Describe the hip joint under type, ligaments, blood supply and movements. Add a note on its dislocation and fracture neck of femur. ★
- Q3Describe the knee joint with its ligaments and menisci. Explain the locking and unlocking mechanism and add a note on its injuries. ★
- Q4Describe the boundaries and contents of the popliteal fossa. Add a note on the sciatic nerve and the effects of its injury. ★
- Q5Describe the arches of the foot and the factors maintaining them. Add a note on the muscles of the sole and weight transmission. ★
- SN1Describe the femoral canal and femoral hernia. Differentiate it from an inguinal hernia. ★
- SN2Describe the course and tributaries of the great saphenous vein. Add a note on varicose veins. ★
- SN3Describe the boundaries and contents of the adductor canal. ★
- SN4Describe the Trendelenburg sign with its mechanism and causes. ★
- SN5Describe the inguinal ligament with its extensions and the structures passing behind it. ★
- SN6Describe the ankle joint with its ligaments and stability. Add a note on ankle sprain. ★
- SN7Compare the upper and lower limbs, explaining the effect of limb bud rotation.