Anterior Interosseous Syndrome is an entrapment neuropathy of the anterior interosseous nerve - a branch of the Median nerve. This nerve branches off from the median nerve, just above the inner elbow. In this condition, the nerve becomes compressed, causing symptoms like pain in the upper arm and difficulty moving the thumb, index finger, and middle finger.
It travels down the forearm and supplies the Flexor Digitorum Profundus, Flexor Pollicis Longus, and Pronator Quadratus muscles.
- Difficulty moving or weakness in the index and middle fingers.
- Difficulty bending the last joint of the thumb, as well as the index and middle fingers.
- Pain in the upper forearm, sometimes even as high as the elbow.
- When pinching with the index finger and thumb, normally a circle is formed. when the AI nerve is compressed, the final joints in the thumb and index fingers are straight rather than bent.
This nerve can be compressed within the forearm by a number of structures, or for a number of reasons. For example:
- An enlarged biceps tendon bursa.
- Fractures (in particular supracondylar fractures) or other traumatic injuries including dislocations.
- The head of Pronator Teres arising deeper than usual.
- Thrombosed radial or ulnar arteries compressing the nerve.