What is the defining symptom of posterior interosseous nerve syndrome?

The defining symptom of posterior interosseous nerve syndrome is finger drop, which occurs due to weakness in the muscles that extend the fingers. The posterior interosseous nerve, a branch of the radial nerve, innervates the extensors of the wrist and fingers, specifically the deep muscles responsible for extending the metacarpophalangeal joints. When this nerve becomes compressed or damaged, the extensor muscles are unable to function properly, leading to the inability to extend the fingers at the knuckle joints.

As a result, the patient will present with a characteristic "wrist drop" or inability to extend the fingers, which is known clinically as finger drop. This symptom is a direct consequence of the loss of motor function in the affected muscles, clearly delineating it as the hallmark sign of posterior interosseous nerve syndrome.

Other choices such as loss of feeling in the fingers and decreased grip strength can occur in various conditions related to nerve or muscle pathology but are not specific to posterior interosseous nerve syndrome. Wrist pain during extension may be related to other conditions affecting the wrist or forearm but does not specifically indicate the presence of this syndrome.