The teres minor is a muscle that attaches each scapula to the humerus. In addition to holding the humerus in the rotator cuff of the shoulder when the deltoid lifts the arm, it also assists with the rotation of the humerus bone.
When the rotator cuff is torn, either in a traumatic injury or by overstress over time, the teres minor often atrophies, causing shoulder pain and a tingling sensation in the arm.