Which ventral rami comprise the lumbar plexus, and what is the typical inclusive root range?

Which ventral rami comprise the lumbar plexus, and what is the typical inclusive root range?

• A. L1–L4 (with possible contribution from T12 and via the lumbosacral trunk, L5)
• B. L2–L5 (no other contributions)
• C. L3–L4 (with T12)
• D. T12–L4

Answer: (A)

The main roots that make up the lumbar plexus are L1 through L4. The plexus forms within the psoas major from these ventral rami and gives rise to nerves that supply the lower abdomen, groin, and thigh. Occasionally, a contribution from the subcostal nerve (T12) can join the plexus, and L5 can feed into the sacral plexus via the lumbosacral trunk. Because of these potential extras, the typical inclusive root range is L1–L4, with possible additions from T12 and L5 through the lumbosacral trunk. This is why the best choice lists L1–L4 as the main range and notes the possible contributions from T12 and via the trunk.

The main roots that make up the lumbar plexus are L1 through L4. The plexus forms within the psoas major from these ventral rami and gives rise to nerves that supply the lower abdomen, groin, and thigh. Occasionally, a contribution from the subcostal nerve (T12) can join the plexus, and L5 can feed into the sacral plexus via the lumbosacral trunk. Because of these potential extras, the typical inclusive root range is L1–L4, with possible additions from T12 and L5 through the lumbosacral trunk. This is why the best choice lists L1–L4 as the main range and notes the possible contributions from T12 and via the trunk.