Ulnar Nerve Lesions Causes, Diagnosis

The brachial nerve plexus gives the ulnar nerve as a branch which runs down the back and inside of the arm to the hand. Muscles in the hand and forearm receive electrical signals from the ulnar nerve. The fourth and fifth fingers (the ring and little fingers) of the hand, a portion of the palm, and the underside of the forearm are all sensed by the ulnar nerve.

In ulnar nerve lesions, the fourth and fifth fingers, as well as the forearm, might experience discomfort, numbness, and tingling. In extreme circumstances, ulnar nerve lesions can result in muscle atrophy and hand weakness.

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Causes of Ulnar Nerve Lesion:

• Prolonged pressure on the elbow or palm's base
• A broken or dislocated elbow
• Bent elbows repeatedly, like while smoking cigarettes
• Sometimes there is no cause to be found.

Ulnar Claw Hand Deformity

An ulnar claw hand deformity is  commonly referred to as a claw hand or a "spinster's claw". It  is a hand deformity or abnormal posture that results from ulnar nerve injury that paralyzes the lumbricals. 

In a claw hand, the proximal and distal interphalangeal joints of the fourth and fifth fingers are flexed and the metacarpophalangeal joints are hyperextended. Although the affected individuals may produce a full fist, their hand posture is known as claw hand when their fingers are extended. The proximal interphalangeal joint (PIP) on the ring- and little-finger typically limits their ability to fully stretch.

Ulnar Paradox

The ulnar (medial) half of the flexor digitorum profundus muscle (FDP) is also innervated by the ulnar nerve. The flexor digitorum profundus muscle may potentially lose nerve supply if the ulnar nerve lesion is more distal (closer to the elbow). 

As a result, the interphalangeal  joints' ability to flex is compromised, which lessens the hand's claw-like appearance. Instead, the fourth and fifth fingers remain completely extended but are paralyzed. The reason this is known as the "ulnar paradox" is that one would often anticipate a more distant and thus incapacitating injury to have a more distorted appearance. The deformity will initially get worse (FDP reinnervated) as the patient recovers because reinnervation happens along the ulnar nerve after a high lesion, which is why the term "paradox" is used.

Related Anatomy Articles :

Ulnar Nerve Injury at Wrist causes More Clawing

Ulnar nerve injury at elbow (behind medial epicondyle) causes Less clawing

Froment Test

Deep muscle of the thumb is supplied by the ulnar nerve that is the adductor pollicis muscle.  This test is used to check adductor pollicis muscle by card test. Hold the card and ask the patient to pull the card. Strong adduction of the thumb in the healthy hand. 

Adductor pollicis helps to hold the card, which is supplied by the ulnar nerve The thumb is flexed at the IP joint, signifying an ulnar nerve lesion. The patient holds the card by folding the thumb with the help of flexor pollicis longus supplied by the AIN branch of the median nerve. Positive froment sign indicating palsy of the adductor pollicis muscle.

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