Froment's sign.

Abstract

Froment’s sign derives its name from Jules Froment (1878–1946) who noted that instances of injury and paralysis to the ulnar nerve resulted in a reduced functionality and muscular weakness in the pinch grip between the thumb and index finger of the affected hand. Froment’s sign presents after damage to the ulnar nerve, which innervates the adductor pollicis and interossei muscles, which provide adduction of the thumb and extension of the interphalangeal joint. The flexor pollicis longus muscle tries to compensate for this loss of power to maintain pressure to the grip by flexing the tip of the thumb at the interphalangeal joint, causing the pinching effect. This is demonstrated by asking the patient to grip a flat object or piece of paper between the thumb and index finger of both hands and to pull in opposite directions. The unaffected hand grasps the surface of the object firmly, using the pulp of the surface of thumb and index finger, with the distal phalanx extended or slightly flexed. The affected hand, however, demonstrates a pinch that is weak, gripping the object with the tips of the thumb and index finger and the distal phalanx of the thumb markedly flexed. The image shown displays the condition in the left hand after ulnar nerve transsection caused by falling onto a smashed coffee mug (Figure 1).