A patient with a spinal cord injury shows a normal patellar reflex but a completely absent Achilles reflex. Which spinal level paraplegia is most likely?

• A. L1 paraplegia
• B. L4 paraplegia
• C. L2 paraplegia
• D. S2 paraplegia

Answer: (B)

Localize by the reflex map: the knee-jerk involves the L3–L4 level, while the ankle-jerk involves the S1–S2 level. If the knee reflex is normal but the ankle reflex is completely absent, the L3–L4 circuitry is functioning while the sacral (S1–S2) reflex arc is disrupted. That pattern points to a lesion at the L4 level, where the pathways controlling the patellar reflex can remain intact, but those influencing the Achilles reflex are affected. If the injury were higher, you’d expect the patellar reflex to be diminished; if it were at S2 or below, the patellar reflex would usually stay intact but the Achilles would be lost due to direct involvement of the sacral roots. In this case, the findings most consistently localize to an L4 paraplegia.