Which nerve is affected by trauma leading to winging of the scapula?

Winging of the scapula is primarily caused by dysfunction of the serratus anterior muscle, which is innervated by the long thoracic nerve. This condition occurs when there is damage or trauma to the long thoracic nerve, preventing it from stimulating the serratus anterior effectively. As a result, the muscle cannot hold the scapula against the thoracic wall, leading to its characteristic winging appearance during arm movements.

The other options refer to nerves that innervate different muscles not directly involved in this specific motion or presentation. The medial pectoral nerve primarily innervates the pectoralis major and minor muscles, and injury to this nerve does not cause winging of the scapula. The suprascapular nerve innervates muscles such as the supraspinatus and infraspinatus and is more involved in shoulder stabilization and external rotation, rather than scapular positioning. The axillary nerve innervates the deltoid and teres minor muscles and is also not responsible for the functionality of the scapula in relation to winging. Therefore, damage to the long thoracic nerve is specifically tied to the winging phenomenon due to its critical role in activating the serratus anterior muscle.