Which spinal level corresponds to knee extension?

Which spinal level corresponds to knee extension?

• A. L2
• B. L3
• C. L4
• D. L5

Answer: (B)

Knee extension is driven by the quadriceps, which are innervated by the femoral nerve coming from the lower lumbar roots. Among these roots, the mid-lumbar myotome is the one most closely tied to knee-extension strength testing, so the L3 level best corresponds to this function. The quadriceps receive strongest input from this level, with L2 contributing mainly to hip flexion and L4 to ankle dorsiflexion, which helps differentiate knee extension from those other movements. Clinically, if knee extension is weak, it points toward involvement at this mid-lumbar level; preservation of hip flexion and ankle dorsiflexion would steer away from higher or lower levels.

Knee extension is driven by the quadriceps, which are innervated by the femoral nerve coming from the lower lumbar roots. Among these roots, the mid-lumbar myotome is the one most closely tied to knee-extension strength testing, so the L3 level best corresponds to this function. The quadriceps receive strongest input from this level, with L2 contributing mainly to hip flexion and L4 to ankle dorsiflexion, which helps differentiate knee extension from those other movements. Clinically, if knee extension is weak, it points toward involvement at this mid-lumbar level; preservation of hip flexion and ankle dorsiflexion would steer away from higher or lower levels.