Nerve Injury Positions of the Hands and Fingers
Written by: Alec Bryson with Dr. Nabil Ebraheim
The presentation of a patient’s hand may provide insight to which nerve is damaged and the approximate location of the damage. When presenting with ulnar n. damage, a patient may show a claw hand, Wartenberg’s sign, or Froment’s sign. Claw hand will present with clawing of the fourth and fifth digits due to the inability to extend the fingers specifically at the interphalangeal joints. This presentation is due to the lack of innervation to the intrinsic muscles of the hands, and the unopposed action of the flexor digitorum profundus m. (Moore et al., 2018). This indicates damage near the distal end of the ulnar n., below the elbow, and potentially near the wrist. Wartenberg’s sign will be seen as the inability to adduct the fifth digit when extended as well as an inability to cross the second and third digit. This is due to ulnar n. injury leading to wasting of the fifth interosseous m. This causes the fifth digit to rest in a more abducted position due to the unbalanced action of the extensor digiti minimi m. (Ebraheim, 2021). There will also be loss of function of the lumbrical m. in the fourth and fifth digits. A Froment’s test will detect palsy of the ulnar n. resulting from compression in the cubital tunnel. When asking the patient to pinch a piece of paper between their thumb and second digit, a positive Froment’s Sign will show as the patient flexing their thumb’s interphalangeal joint to grip the paper as the paper is pulled away (Attum, 2021). This will result from a weak adductor pollicis m. due to ulnar n. palsy.
Depending on the location of a lesion to the median n., the patient will present with one of three signs. A positive Benedictine sign will be caused by proximal median n. damage. It will be seen as paralysis of the first and second digit, with weakness to the third digit. A proximal lesion would lead to paralysis of several muscles (FDS, FPL, FPB, and the radial half of FDP), leaving the ulnar half of the flexor digitorum profundus m. as the only remaining flexor (Ebraheim, 2021). When the patient is asked to make a fist, the hand will resemble the similar position taken during a blessing. A positive Benedict sign will also resemble the ulnar claw hand. However, the Benedict sign will present when the patient is flexing, not extending the fingers (Ebraheim, 2021). A median n. injury affecting the anterior interosseous n. branch will present as an inability to do the OK sign. This occurs due to paralysis of the flexor pollicus longus m. and the lateral part of the flexor digitorum m. (Moore et al., 2018). A positive Ape hand (Simian hand) is caused by paralysis of only the thenar m. from damage to the recurrent branch of the median n. to the thenar m. The thumb will be seen in the same plane as the other digits due the thumb being pulled more dorsal by the action of the adductor pollicis m., which is innervated by the ulnar n. (Moore et al., 2018).
Finally, proximal radial n. damage will be seen as wrist drop. This is usually caused by fractures of the distal third of the humeral shaft (Holstein-Lewis Fracture) and caused paralysis of the wrist and fingers extensors (Ebraheim, 2010). Lower radial n. injury will present in the patient as the ability to extend the wrist, but the loss of finger extension. There will be no wrist drop, but the patient would not be able to make a hitchhiking sign.
Reference List
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Everything You Need To Know - Dr. Nabil Ebraheim [Internet]. YouTube. 2021
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2021 [cited 2021Oct21]. Available from:
https://www.youtube.com/watch?v=nwd1h0Dfo5o
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