Posterior Interosseous Nerve (PIN) syndrome is a compressive neuropathy in the proximal forearm. While it causes profound motor weakness resulting in ‘finger drop’, what is its classic sensory presentation?

Explanation:
The correct option is c. The radial nerve bifurcates in the proximal forearm into the superficial radial nerve (purely sensory) and the posterior interosseous nerve (purely motor). The PIN dives through the supinator muscle (Arcade of Frohse), where it can be compressed. Because the PIN carries strictly motor fibers to the extensor compartment (and some proprioceptive fibers to the dorsal wrist capsule), PIN syndrome presents with weakness in extending the MCP joints and the thumb (finger drop/thumb drop) with absolutely NO cutaneous sensory loss. If there is numbness in the dorsal web space, the lesion must be higher up the arm, involving the main radial nerve trunk. Reference: Green's Operative Hand Surgery.