Final answer:
Crutch palsy commonly affects the axillary nerve, which originates from the brachial plexus and supplies motor and sensory functions to the shoulder.
Step-by-step explanation:
The nerve that is commonly injured due to repetitive pressure or trauma within the axilla, often referred to as "Crutch palsy," is the axillary nerve. This nerve arises from the brachial plexus, which is associated with the lower cervical spinal nerves and the first thoracic spinal nerve. The axillary nerve is a systemic nerve of the arm that plays a crucial role in the movement and sensory supply of the shoulder. Prolonged pressure, such as that from the improper use of crutches, can cause damage to this nerve, leading to weakness or paralysis of the deltoid muscle, loss of sensation in the skin covering the deltoid area, and sometimes also affecting the teres minor muscle.