What motor function loss is expected with an anterior interosseous nerve injury?

The anterior interosseous nerve is a branch of the median nerve, primarily supplying the deep flexor muscles of the forearm, specifically the flexor pollicis longus and the lateral half of the flexor digitorum profundus. When an injury occurs to this nerve, the specific muscle functions it innervates are affected, leading to pinpointed motor function loss.

The loss of "thumb to tip for pinch" refers to the inability to perform a pinch grip that requires the opposition of the thumb and the index finger, critical for grasping and manipulating objects. This function is particularly reliant on the action of the flexor pollicis longus, which allows for flexion of the thumb at the interphalangeal joint, and the flexor digitorum profundus for flexing the distal phalanx of the index finger. In other words, when the anterior interosseous nerve is compromised, the coordination required for this precise movement is lost, making it the expected outcome of such an injury.

In contrast, the other options relate to different nerve injuries or muscle groups. Loss of wrist extension is associated with a radial nerve injury, loss of finger abduction relates to ulnar nerve impairment affecting the interossei muscles