At the L1 level, how is trunk function described?

At the L1 level, how is trunk function described?

• A. Complete trunk function
• B. No trunk function
• C. Partial trunk function
• D. Trunk function not described

Answer: (A)

At this level, trunk control is preserved because the muscles that form the trunk (the abdominal wall and back extensors) are innervated by nerves that originate above this level. In spinal level classification for neural tube defects, the neurologic level is the most caudal intact segment, and since the trunk muscles get their innervation from higher (thoracic) levels, trunk function remains fully intact. This means the trunk can maintain posture and stability even if there may be weakness in the legs due to involvement of lower nerve roots. Therefore, describing trunk function as complete best fits the physiological pattern at this level.