Anterior Interosseous Syndrome

Anterior interosseous syndrome

Anterior Interosseous Syndrome is the entrapment of a branch of the Median nerve, just above the elbow. The nerve becomes compressed, causing symptoms of pain in the upper arm and difficulty moving the thumb, index finger, and middle finger.


  • Difficulty moving your index and middle fingers.
  • Or you may have a specific weakness in these fingers.
  • Bending the last joint of your thumb may be hard to do, as well as the index and middle fingers.
  • Pain in the upper forearm, sometimes as high as the elbow.
  • When pinching with your index finger and thumb together, normally a circle is formed. However, if you have Anterior Interosseous syndrome, the end (distal) joints in the thumb and index fingers are straight, rather than bent.

Assessment tests

The ‘Pinch Grip’ test is used to identify compression of the median nerve.

What causes Anterior Interosseous Syndrome?

It is caused by compression of the median nerve within the forearm. The branch of the median nerve travels down the forearm and supplies the Flexor Digitorum Profundus, Flexor Pollicis Longus, and Pronator Quadratus muscles. There are a number of structures that cause this to happen for various reasons. These include:

  • An enlarged biceps tendon bursa. A bursa is a small sack of fluid found between a tendon and bone. its function is to aid movement of the tendon.
  • Fractures, in particular supracondylar fractures of the humerus bone, just above the elbow.
  • Other traumatic injuries including dislocations can also result in Anterior interosseous syndrome.
  • The head (end) of Pronator teres muscle arising deeper than usual. The pronator teres muscle connects the humerus to the radius bone and enables the forearm to pronate (turn inwards).
Pronator teres syndrome
Pronator teres muscle
  • Thrombosed radial or ulnar arteries compressing the nerve. A thrombosis is a blot clot.


  • Initial conservative treatment for Anterior interosseous syndrome is rest, splinting, and anti-inflammatory medications. Always check with your doctor before taking medications. Ibuprofen is a popular anti-inflammatory drug, but you should not take this if you have Asthma.
  • Corticosteroid or nerve block injections may be used.
  • Surgery to release the nerve is sometimes used if conservative treatment fails.

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