Dr. Ebraheim’s educational animated video describes positions of the hand and fingers that may identify possible nerve injuries.
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When you examine a patient with a nerve injury, if you look at the hand, you may be able to determine what kind of nerve injury the patient may have. And an ulnar nerve injury, you may have a claw hand, you may have Wartenberg's sign, the patient may not be able to cross the fingers and you may have wasting of the first interosseous muscle. Injury to the ulnar nerve may produce a clawhand deformity, especially if the injury is below the elbow. The flexion of the fingers or the clawing of the fingers occurs due to a functional flexor digitorum profundus muscle for the fourth and fifth fingers (the FDP is working for these fingers). The flexor digitorum profundus takes over and causes clawing of the fingers. When the hand is relaxed or extended the claw appearance disappears. In the distal ulnar nerve injury, you lose innervation to all of the interossei in the ulnar 2 lumbricals.Wartenberg's sign is and abduction of the fifth finger. Wartenberg's sign is due to an ulnar nerve injury and consist of abduction of the fifth finger, caused by an unopposed action of the ulnar insertion of the extensor digiti quinti (radial nerve innervated muscle). The unopposed action of the extensor digiti quinti muscle causes the finger to rest in a more abducted position.
Why does Wartenberg's sign happen? It occurs due to paralysis of the palmar interosseous muscle that abducts the little finger. The patient will be unable to cross the middle and index finger as a result of ulnar nerve injury. Abduction of the fingers come from the dorsal interossei (DAB).
Froment's test is used frequently to test for palsy of the ulnar nerve which may occur with entrapment of the ulnar nerve within the cubital tunnel (cubital tunnel syndrome). Formant sign is a test for the ulnar nerve. When pinching a piece of paper between the thumb and index finger, the thumb IP joint will flex if the abductor pollicis muscle is weak due to an ulnar nerve palsy. The anterior interosseous nerve is of branch of the median nerve. The "hand of benediction "is seen in patients with a high median nerve injury. The "sign of benediction" is an active sign that occurs when a patient with a high median nerve injury is trying to make a fist. In the sign of benediction (due to high median nerve injury) there will be paralysis of the FDS, the FPL, the FPB and the radial half of the FDP. So, the only remaining flexor that is functioning is the ulnar half of the FDP, which resulted in flexion of digits 4 and 5, while the other digits remain extended. The first and second digits will have difficulty in flexing, will the other digits (4 and 5 digits) will flex. The third digit appears to be weak. Hand will assume the Benedictine sign or sign of benediction. Ulnar claw hand refers to damage to the ulnar nerve
below the elbow and is seen when the patient is attempting to extend all the digits (leaving the fourth and fifth digits flexed). In a normal hand at rest, digits 2 through 5 assume a mild flexion position and all will be in the same dorsal ventral plane due to the action of the thenar muscles. In a median nerve injury, the thenar muscles are paralyzed so the thumb will be pulled more dorsal by the action of the adductor pollicis, which is an ulnar nerve innervated muscle. The thumb will be in the same plane as the other digits. All the digits lined up in the same dorsal ventral plane resembles the hand position of lower primates, which is why they called this "ape hand."
The O.K. sign Patients with paralysis of the anterior interosseous nerve will be unable to make the okay sign. This occurs due to paralysis of the FPL muscle and the lateral part of the flexor digitorum muscle (both are innervated by the anterior interosseous nerve).
High radial nerve palsy (upper arm to elbow)
Injury to the radial nerve will cause wrist drop. High radial nerve injury is usually occur due to fractures of the distal third of the humeral shaft.
Holstein–Lewis fracture
The fracture will cause injury to the radial nerve which will result in paralysis of the wrist and finger extensors (22%). The patient will not be able to extend the wrist, fingers or the thumb (occurs in about 20% of patients). The patient will not be able to hitchhike or do finger extension.
Low radial nerve palsies (below elbow)Low radial nerve injury usually occurs around the elbow and it will affect fingers and thumb extension (posterior interosseous nerve injury). If the patient does not have a wrist drop and still cannot perform the hitchhike sign, and check the patient for posterior interosseous nerve injury. Recovery of wrist extensors, but the finger extensors are not yet recovered is a sign of posterior interosseous nerve injury that has not recovered yet.
