Final answer:
The axillary nerve is probably injured in a patient who cannot abduct the arm between 0 and 15 degrees and has reduced lateral rotation; it innervates muscles responsible for these movements.
Step-by-step explanation:
The patient with a gunshot wound to the shoulder who is unable to abduct the arm between 0 and 15 degrees and has reduced lateral rotation of the humerus is likely suffering from an injury to the axillary nerve. This nerve is responsible for innervating the deltoid and teres minor muscles, which contribute to the abduction and lateral rotation of the arm. The accessory nerve, on the other hand, innervates the sternocleidomastoid and trapezius muscles, primarily affecting head and neck movements, and is therefore not the correct answer. The median and ulnar nerves are primarily associated with the forearm and hand, and the suprascapular nerve mainly controls the supraspinatus and infraspinatus muscles; these are not typically involved in the initial 0 to 15 degrees of arm abduction