A herniation at L4-L5 most commonly affects which nerve root?

A herniation at L4-L5 most commonly affects which nerve root?

• A. L5
• B. L4
• C. S1
• D. L3

Answer: (D)

When a lumbar disc herniates, the nerve root most likely affected is the one that exits just below the level of the herniation. For a disc herniation between L4 and L5, the L5 nerve root is compressed because it travels through the foramen below that disc level. That pattern—disc at a given level impinging the nerve root that exits below it—is why L5 is the commonly involved root here. If the herniation were at a different level, a different nerve root would be implicated (for example, a disc at L3-L4 would more likely affect L4, and a disc at L5-S1 would affect S1).

When a lumbar disc herniates, the nerve root most likely affected is the one that exits just below the level of the herniation. For a disc herniation between L4 and L5, the L5 nerve root is compressed because it travels through the foramen below that disc level. That pattern—disc at a given level impinging the nerve root that exits below it—is why L5 is the commonly involved root here. If the herniation were at a different level, a different nerve root would be implicated (for example, a disc at L3-L4 would more likely affect L4, and a disc at L5-S1 would affect S1).