Knee extension is primarily controlled by which myotome?

Knee extension is primarily controlled by which myotome?

• A. L2
• B. L3
• C. L4
• D. L5

Answer: (B)

Knee extension is carried out by the quadriceps muscles, which are innervated by the femoral nerve arising from the upper lumbar spinal roots. Among those roots, the myotomal level most strongly linked to extending the knee is the one that supplies the quadriceps. That’s why knee extension is tested by having the patient straighten the knee against resistance—the strength here primarily reflects the function of that lumbar myotome. If this root is impaired, you’ll see weakness in extending the knee, whereas movements controlled mainly by nearby or different myotomes (like dorsiflexion, which involves a different level) would be affected differently.

Knee extension is carried out by the quadriceps muscles, which are innervated by the femoral nerve arising from the upper lumbar spinal roots. Among those roots, the myotomal level most strongly linked to extending the knee is the one that supplies the quadriceps. That’s why knee extension is tested by having the patient straighten the knee against resistance—the strength here primarily reflects the function of that lumbar myotome. If this root is impaired, you’ll see weakness in extending the knee, whereas movements controlled mainly by nearby or different myotomes (like dorsiflexion, which involves a different level) would be affected differently.