What is a potential consequence of cutting the thoracodorsal nerve?

• A. Weakness in shoulder abduction
• B. Loss of sensation over the arm
• C. Weakness in arm extension
• D. Weakness in scapular rotation

Answer: (C)

Cutting the thoracodorsal nerve can lead to weakness in arm extension primarily because this nerve innervates the latissimus dorsi muscle, which plays a crucial role in extending the arm at the shoulder joint. The latissimus dorsi is responsible for movements such as adduction, extension, and medial rotation of the arm. When the nerve is damaged, the functionality of this muscle is impaired, which means that the ability to extend the arm would be compromised, resulting in noticeable weakness, especially during activities that involve lifting or reaching behind.

The other choices, while relating to different functions and muscles, do not directly correlate with the thoracodorsal nerve's primary responsibility. Weakness in shoulder abduction is mainly associated with issues relating to the deltoid or supraspinatus muscles, which are innervated by different nerves. Loss of sensation over the arm typically pertains to sensory nerves rather than motor nerves like the thoracodorsal. Weakness in scapular rotation involves muscles such as the serratus anterior, which is innervated by the long thoracic nerve. Thus, the impact of cutting the thoracodorsal nerve specifically leads to issues with arm extension.