Review Question - QID 2951

A deficit in the anterior interosseous nerve (AIN) would result in an inability to flex the interphalangeal joint (IPJ) of the thumb.

Injury to the AIN can be seen with K-wires that penetrate through the anterior cortex of the proximal ulna, such as mentioned above. The AIN is a branch of the median nerve that provides motor function to forearm/hand. It branches off from the median nerve 4 cm distal to the medial epicondyle, passes between the 2 heads of the pronator teres, travels through the forearm anterior to the interosseous membrane between the flexor pollicis longs (FPL) and flexor digitorum profundus (FDP), and then terminates in the pronator quadratus (PQ). The nerve gives of branches to the FDP, FPL, and PQ enabling for flexion of the distal phalangeal joint of the index and middle fingers, flexion of the IPJ of the thumb, and aids with pronation of the forearm, respectively. Injury to the nerve will result in weakness in motor function to these muscles.

Mekail et al. reviewed the anterior approach to the proximal radius in order to describe and identify important neurovascular and musculoskeletal structures in the area. They were specifically aiming to determine the safest anatomic orientation for plate and screw fixation in regards to the posterior interosseous nerve. The authors, however, did discuss that medial plating was especially dangerous to the AIN, and significantly increased the risk of iatrogenic injury to the branch sent to the FPL.

Parker et al. reported a case report in a patient who experienced an AIN deficit postoperatively after tension banding of an olecranon fracture. Intraoperatively, there were multiple passes of the K-wires in an attempt to find purchase in the anterior cortex of the ulna. The authors believed that during these passes, the nerve was injured and concluded that placing K-wires should not occur without radiologic visualization.

Figure A is a postoperative lateral radiograph after tension banding of the olecranon. Perforation of the anterior ulnar cortex can be seen by the K-wire which can cause damage to the AIN nerve. Illustration A is a schematic of the path of the AIN, its branches, and its function.

Incorrect Answers:
Answer 1: Both ulnar and median nerves provide innervation muscles that flex the radoiocarpal joint.
Answer 2: AIN has no cutaneous sensory fibers. Median nerve disruption would result in this deficit.
Answer 3: Disruption of the superficial radial serve would result in this deficit..
Answer 4: Disruption of the deep branch of the ulnar nerve would result in this deficit.