Posterior interosseous nerve syndrome

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October 29, 2014

The radial nerve is the terminal branch of the posterior cord of the brachial plexus, containing nerve fibers from C5-8 and T1. It bifurcates into its deep and superficial branches anterior to the lateral condyle, forming the posterior interosseous nerve (PIN) as it enters the supinator muscle at the arcade of Frohse. Compression of, or pathology to this nerve, often results in the posterior interosseous nerve syndrome. Masses such as lipomas or ganglia, bony overgrowths, traumatic accidents, and the fibrous nature of the arcade of Frohse are all proposed mechanisms to cause PIN syndrome. Clinically, patients present with radial deviation of the wrist during extension due to impairment of the extensor carpi ulnaris, as well as “finger drop.” The syndrome is felt to be non-painful and is usually diagnosed by electromyography and nerve conduction studies demonstrating focal slowing or conduction block. More recently, ultrasound has been shown to demonstrate an increased nerve diameter with compressive lesions.


  1. Dang AC and Rodner CM. Unusual compression neuropathies of the forearm, part I: radial nerve.  J Hand Surg Am 2009; 34: 1906-1914.
  2. Djurdjevic T et al. High resolution ultrasound in posterior interosseous nerve syndrome.  Muscle Nerve 2014; 49: 35-39.

Submitted by James Addington, MD, Resident Physician, Department of Neurology, University of Virginia.

Dr. Addington is a member of the Resident and Fellow Section of Neurology.

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