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)

In the low lumbar region, the muscle functions most closely tied to the L4-L5 myotomes include ankle dorsiflexion. This movement is carried mainly by the tibialis anterior, which is innervated by the L4-L5 nerve roots. So, when testing L4-L5, you’d expect to see strength in ankle dorsiflexion and potentially weakness there if those roots are affected, which would make foot clearance during walking more difficult (a foot-drop pattern). Other options point to different levels: ankle plantarflexion relies largely on S1 (and sometimes S2), knee extension is L3-L4 (quadriceps), and hip adduction is primarily L2-L4 (adductor muscles). Therefore ankle dorsiflexion best corresponds to the L4-L5 level.

In the low lumbar region, the muscle functions most closely tied to the L4-L5 myotomes include ankle dorsiflexion. This movement is carried mainly by the tibialis anterior, which is innervated by the L4-L5 nerve roots. So, when testing L4-L5, you’d expect to see strength in ankle dorsiflexion and potentially weakness there if those roots are affected, which would make foot clearance during walking more difficult (a foot-drop pattern).

Other options point to different levels: ankle plantarflexion relies largely on S1 (and sometimes S2), knee extension is L3-L4 (quadriceps), and hip adduction is primarily L2-L4 (adductor muscles). Therefore ankle dorsiflexion best corresponds to the L4-L5 level.