Which muscle is tested to determine the L5 motor level in ASIA?

Which muscle is tested to determine the L5 motor level in ASIA?

• A. Tibialis anterior
• B. Extensor hallucis longus
• C. Quadriceps (L3)
• D. Hamstrings (L4)

Answer: (B)

In this assessment, the motor level for each spinal segment is determined by testing a specific key muscle that corresponds to that level. For the L5 level, the designated muscle is the extensor hallucis longus, which is responsible for extending the big toe. If this muscle shows preserved strength (typically at least 3/5) while muscles above it are normal, the L5 motor level is identified. The other muscles map to different levels—tibialis anterior tests L4 (ankle dorsiflexion), quadriceps tests L3 (knee extension)—so they do not indicate L5. Therefore, extensor hallucis longus is the correct muscle to assess for the L5 motor level.

In this assessment, the motor level for each spinal segment is determined by testing a specific key muscle that corresponds to that level. For the L5 level, the designated muscle is the extensor hallucis longus, which is responsible for extending the big toe. If this muscle shows preserved strength (typically at least 3/5) while muscles above it are normal, the L5 motor level is identified. The other muscles map to different levels—tibialis anterior tests L4 (ankle dorsiflexion), quadriceps tests L3 (knee extension)—so they do not indicate L5. Therefore, extensor hallucis longus is the correct muscle to assess for the L5 motor level.