Final answer:
An anterior interosseous nerve injury can result in weakness or paralysis of the forearm muscles, particularly affecting the 'pinch grip' function due to impaired innervation of the flexor pollicis longus and flexor digitorum profundus muscles.
Step-by-step explanation:
An anterior interosseous nerve injury will primarily affect the muscles in the anterior compartment of the forearm responsible for flexion of the thumb and fingers. Specifically, the flexor pollicis longus and the flexor digitorum profundus, which are innervated by the anterior interosseous nerve, will be compromised. This can result in the inability to perform the 'pinch grip' where the thumb and tip of the index finger are brought together. Such an injury can occur due to trauma, such as a fracture of the bones in the forearm (humerus, radius, ulna), sometimes affecting the interosseous membrane, thereby causing instability and potentially damaging the interosseous nerves if not properly immobilized. Without proper nervous stimulation, affected muscles may weaken and atrophy, similar to the decrease in muscle strength seen in cases of carpal tunnel syndrome, which also involves compression of a nerve (median nerve) in the forearm.