Which muscle function is expected in low lumbar L4-L5?

Which muscle function is expected in low lumbar L4-L5?

• A. Ankle dorsiflexion
• B. Ankle plantarflexion
• C. Knee extension
• D. Hip adduction

Answer: (A)

Myotome knowledge tells us what motor function to expect from specific spinal levels. The L4-L5 roots primarily control ankle dorsiflexion, with the tibialis anterior receiving innervation from the deep peroneal nerve at this level. Dorsiflexion is crucial for lifting the foot during the swing phase of gait, and its strength indicates intact L4-L5 function. In contrast, knee extension is mainly L3-L4, ankle plantarflexion is largely S1-S2, and hip adduction involves L2-L4, so those functions map to different levels. Therefore, ankle dorsiflexion is the expected muscle function at low lumbar L4-L5.