The most common complication of anterior dislocation of the shoulder is axillary (circumflex) nerve injury. There is consequent paralysis of the deltoid muscle, with a small area of anaesthesia at the lateral aspect of the upper arm. However, in this question, the sensation is lost on the lateral aspect of the forearm (not arm). The lateral side of the forearm has sensory supply from the lateral cutaneous nerve of foreign, a branch of musculocutaneous nerve. The musculocutaneous nerve also supplies the biceps brachii (a flexor of elbow joint). Therefore, musculocutaneous nerve injury will cause sensory loss over the lateral aspect of the forearm with the weakness of flexion at the elbow. As occasionally other branches of brachial plexus (other than axillary nerve) can also be injured, the answer to this question is a musculocutaneous nerve.