Which movement is tested by the L3 myotome?

Which movement is tested by the L3 myotome?

• A. Knee extension
• B. Hip flexion
• C. Elbow extension and wrist flexion
• D. Finger abduction and adduction

Answer: (A)

The movement most associated with the L3 myotome is knee extension, produced by the quadriceps muscle group. The quadriceps straighten the knee and receive their nerve supply from the femoral nerve, which carries signals from L2 to L4; testing knee extension against resistance directly assesses L3 function within that pattern. In a practical exam, have the patient sit with the leg hanging and try to straighten the knee while you apply resistance, or place your hand against the shin and ask them to push the leg out straight. Normal knee extension suggests intact L3, while weakness or inability to extend the knee points to L3 involvement. The other movements correspond to different nerve roots or regions (elbow extension and wrist flexion to higher cervical levels; finger abduction/adduction to hand intrinsic muscles and different roots), so they don’t reflect the L3 myotome.

The movement most associated with the L3 myotome is knee extension, produced by the quadriceps muscle group. The quadriceps straighten the knee and receive their nerve supply from the femoral nerve, which carries signals from L2 to L4; testing knee extension against resistance directly assesses L3 function within that pattern. In a practical exam, have the patient sit with the leg hanging and try to straighten the knee while you apply resistance, or place your hand against the shin and ask them to push the leg out straight. Normal knee extension suggests intact L3, while weakness or inability to extend the knee points to L3 involvement. The other movements correspond to different nerve roots or regions (elbow extension and wrist flexion to higher cervical levels; finger abduction/adduction to hand intrinsic muscles and different roots), so they don’t reflect the L3 myotome.