The “Texas Longhorn” Syndrome: A Case of Posterior Interosseous Nerve Palsy With Noteworthy Observations

The posterior interosseous nerve (PIN) is quite a fascinating nerve. It wraps around the radial neck akin to the fibular nerve wrapping around the fibular neck. It can be compressed by the arcade of Frohse in a fashion similar to median nerve entrapment by the carpal tunnel. Furthermore, it divides into a number of branches, a simulacrum of the cauda equina, as it emerges from the supinator muscle. It is also associated with space-occupying pathologies; lipomas, and ganglion cysts being among the most common. It also has other interesting anatomical properties, such as fascicular compartmentalization, explaining PIN paralysis with radial nerve injuries. Finally, PIN lesions can lead to partial paralysis of finger extensors leading to the "Texas longhorn" hand gesture. We seize upon a case of PIN entrapment by fibrous adhesions and the arcade of Frohse, and explore the functional anatomy of the PIN.