How can radial nerve damage be identified in a patient with a midshaft humeral fracture?

Radial nerve damage is commonly associated with midshaft humeral fractures due to the anatomical course of the nerve along the shaft of the humerus. One of the hallmark signs of radial nerve injury is the inability to extend the fingers, which is a direct result of the paralysis of the extensor muscles supplied by the radial nerve. When the radial nerve is compromised, the patient will present with wrist drop and an inability to actively extend the fingers at the metacarpophalangeal joints. This loss of function can be evaluated by observing the patient's ability to extend digits against gravity.

In contrast, other options represent different nerve injuries or conditions. Inability to flex fingers typically indicates median or ulnar nerve injury. Absence of sensation to pinprick over the palm points to issues with the median or ulnar nerves supplying sensory innervation to that area. Loss of thumb opposition is related to median nerve damage, specifically affecting the ability to bring the thumb into opposition with the other fingers. Therefore, the identifying symptom of radial nerve damage in the context of a midshaft humeral fracture is specifically the inability to extend the fingers.