Question

Which nerve will be commonly involved if the injury occurs at the marked levels?

• A. L4
• B. L5
• C. L2
• D. L3

Hint:

L5 nerve root lesions are often associated with foot drop and weakness in the dorsiflexion of the foot, and they are common in lumbar spine injuries.

Answer 1

The Correct Option is B

Step 1: Read what the marked level supplies.
The injury is flagged at a lower lumbar segment. To name the nerve, ask which root governs the motor sign that level is known for. The hallmark of this root is dorsiflexion of the foot (lifting the foot and great toe upward) plus sensation over the dorsum of the foot - that motor function points to L5.

Step 2: Build the lumbar root map for cross-checking.
• L2 - hip flexion.
• L3 - knee extension.
• L4 - quadriceps and the knee-jerk reflex.
• L5 - dorsiflexion (foot/great-toe lift), the function tied to the marked level.

Step 3: Apply clinical frequency.
The L5 root is one of the most commonly injured because of its weight-bearing position and the mechanical stress at the lower lumbar spine, so a lesion at the marked level characteristically disturbs the foot-lifting (extensor) muscles it controls.

Step 4: Conclude.
The root that matches both the segment marked and the dorsiflexion deficit is L5.

Final answer: Option 2 - L5.