Microscopic Anatomy of the Posterior Interosseous and Median Nerves at Sites of Potential Entrapment in the Forearm

We describe the macroscopic and microscopic anatomy of the posterior interosseous (PIN) and median nerves, at the arcade of Frohse and pronator arch respectively, in nerves obtained from five cadavers. Nerves were either constricted at sites of potential entrapment; appeared swollen proximal to these sites; or exhibited neither swelling nor constriction. Renaut bodies were present in all nerves. In the PIN, most Renaut bodies were found beneath a tendinous arcade of Frohse, whereas in the median nerve most were found proximal to the pronator arch. We propose that since Renaut bodies appear to displace normal endoneurial components, and may be associated with low-grade axonal drop-out, their presence may adversely affect the functional outcome of surgical decompression of either the PIN or median nerve.