A 24-year-old lady is stabbed in the buttock. Following the injury, the wound is sutured in the emergency department. Eight weeks later, she attends the clinic. As she walks into the clinic room, she has a waddling gait and difficulty with thigh abduction. On examination, she has buttock muscle wasting. Which nerve has been injured?
A. Superior gluteal nerve
B. Obturator nerve
C. Sciatic nerve
D. Femoral nerve
E. Inferior gluteal nerve
Correct Answer: A. Superior gluteal nerve
Explanation:
The superior gluteal nerve innervates the gluteus medius, gluteus minimus, and tensor fasciae latae, which are responsible for hip abduction and maintaining pelvic stability during walking. Injury to this nerve results in:
- Waddling gait (Trendelenburg gait): Due to weakened gluteus medius and minimus, causing pelvic drop on the contralateral side during walking.
- Difficulty with thigh abduction: The primary muscles responsible for abduction are denervated.
- Buttock muscle wasting: Prolonged injury leads to atrophy of the gluteal muscles.
This clinical presentation—difficulty walking, impaired abduction, and muscle wasting—fits a superior gluteal nerve injury.
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Trendelenburg Test
Injury or division of the superior gluteal nerve results in a motor deficit, causing weakness in thigh abduction by the gluteus medius, leading to a gluteus medius limp and compensatory leaning of the body toward the weakened side. This compensation shifts the body’s center of gravity, allowing the unaffected limb to bear the weight.
During the Trendelenburg test, the patient is asked to stand on one leg. Normally, as the contralateral leg lifts off the floor, the gluteus medius contracts to stabilize the pelvis, preventing it from dropping toward the unsupported side. However, in a person with superior gluteal nerve paralysis, the pelvis on the affected side drops, indicating that the gluteus medius on the stance leg is weak or nonfunctional. This is a positive Trendelenburg sign.
Note:
The direction of the pelvic drop during a positive Trendelenburg sign corresponds to the affected side where the gluteus medius is weak or nonfunctional due to superior gluteal nerve injury. Therefore, a pelvic drop on the left side indicates left-sided nerve injury.
“Understanding Hip Abduction: Anatomy, Function, and Clinical Significance”
Incorrect Option Analysis:
B. Obturator nerve
The obturator nerve controls the adductor muscles of the thigh, which are responsible for thigh adduction. Its injury would cause difficulty bringing the thigh toward the midline and sensory loss over the medial thigh. This is not consistent with the patient’s difficulty in abduction.
C. Sciatic nerve
The sciatic nerve innervates the hamstrings and muscles of the leg and foot. Injury would cause deficits like weakness in knee flexion, foot movements, and sensory loss in the leg and foot. The local nature of this patient’s symptoms points away from a sciatic nerve injury.
D. Femoral nerve
The femoral nerve controls the quadriceps, which are responsible for knee extension, and provides sensation to the anterior thigh and medial leg. Injury to the femoral nerve would cause difficulty with knee extension, not hip abduction or gluteal muscle wasting.
E. Inferior gluteal nerve
The inferior gluteal nerve innervates the gluteus maximus, responsible for hip extension and lateral rotation. Injury to this nerve would cause difficulty with activities like rising from a seated position or climbing stairs, but would not produce the waddling gait or difficulty with abduction seen in this case.
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Gluteus Medius
- Origin: Outer surface of the ilium, between the anterior and posterior gluteal lines.
- Insertion: Lateral surface of the greater trochanter of the femur.
Gluteus Minimus
- Origin: Outer surface of the ilium, between the anterior and inferior gluteal lines.
- Insertion: Anterior surface of the greater trochanter of the femur.
Both muscles play critical roles in hip abduction and pelvic stabilization during gait. They are innervated by the superior gluteal nerve (L4-S1).
What is Hip Abduction?
Hip abduction is the movement of the leg away from the midline of the body in the frontal plane. This action occurs at the hip joint and is vital for activities like walking, running, and balancing.
Muscles Responsible for Hip Abduction
- Gluteus Medius (primary abductor)
- Gluteus Minimus (assists gluteus medius)
- Tensor Fasciae Latae
- Piriformis (secondary abductor when the hip is flexed)
- Sartorius (aiding role)
Functions of Hip Abduction
- Pelvic Stability: During walking or running, hip abductors stabilize the pelvis, preventing it from tilting toward the unsupported side (contralateral pelvic drop).
- Leg Movement: Moves the leg outward, essential for lateral movements.
- Weight Distribution: Balances the body when standing on one leg.
Clinical Relevance
Injury to the superior gluteal nerve can weaken hip abductors, leading to a Trendelenburg gait, where the pelvis drops on the opposite side during walking.