Isolated flexor pollicis longus nerve fascicle lesion – a rare differential diagnosis of thumb flexion deficiency

Abstract

A rare differential diagnosis of thumb flexion deficiency is an isolated flexor pollicis longus (FPL) nerve fascicle lesion. We present a 42-year-old otherwise healthy female patient who developed a weak thumb-to-index pinch and deficient right thumb flexion following the removal of osteosynthesis plates after a forearm fracture. Clinically,the flexor pollicis longus function was absent, yet index flexion and sensibility were unimpaired. Tendon rupture was excluded using a tenodesis test and the electro-physiological result of isolated interosseus nerve fascicle lesion was confirmed intraoperatively by inspection and electrostimulation. Tendon transfer using the extensor carpi radialis longus reconstruct strong thumb flexion during pinch. In summary, due to its specific location and anatomy, the FPL branch is more prone to isolated neuropathy, e.g. by injections or operations, than to other fascicles of the anterior interosseus nerve. When confronted with sudden and isolated thumb flexion deficiency, specialists should be aware of this rare phenomenon.

Keywords

• anterior interosseous nerve
• thumb flexion
• flexor pollicis longus
• isolated