Describe Froment's sign and the anatomical structures involved. Explain the clinical significance of thenar muscle weakness and loss of thumb opposition, considering sensory involvement.

You're on a roll — here are the solutions to the questions: Question 64: The correct answer is B. Froment's sign* is a clinical test for ulnar nerve palsy. It is positive when a patient cannot hold a piece of paper between their thumb and the lateral side of their index finger without flexing the interphalangeal joint of the thumb. This compensatory flexion occurs because the adductor pollicis muscle, which is primarily responsible for thumb adduction and is innervated by the ulnar nerve, is weak. To compensate for the weak adductor pollicis, the patient uses the flexor pollicis longus* (innervated by the median nerve) to pinch the paper, resulting in flexion of the thumb's interphalangeal joint. Therefore, weakness of the adductor pollicis causes this sign. Question 65: The correct answer is C. The patient's symptoms of "profound weakness in the thumb, with loss of thumb opposition" indicate damage to the thenar muscles, particularly the opponens pollicis*, which is responsible for thumb opposition. The crucial detail is that "sensation to the hand, however, was unaffected." This points to an injury of a purely motor nerve*. During an endoscopic carpal tunnel release, the recurrent motor branch of the median nerve* (also known as the thenar motor branch) is particularly vulnerable to injury. This branch arises from the median nerve distal to the carpal tunnel and supplies the thenar muscles (abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis) without carrying any sensory fibers. Injury to this nerve would explain the isolated motor deficit without sensory loss. Drop the next question 📸