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Ulnar claw: Wikis

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An ulnar claw is an abnormal hand position that develops due to a problem with the ulnar nerve. It should not be confused with the hand of benediction which results from a median nerve injury, and presents as an inability to flex the thumb, the index and middle fingers when asked to make a fist.

Contents

Presentation

The hand will show hyper-extension of the metacarpophalangeal joints (MCP) and flexion at the distal and proximal Interphalangeal (IP) joints of the 4th and 5th digits (ring and little finger) [1]. The clawing will become most obvious when the person is asked to straighten their fingers.[2]

Pathogenesis

An ulnar claw may follow an ulnar nerve lesion[3] which results in the partial or complete denervation of the medial two lumbricals of the hand. Since the lumbricals normally flex the MCP joints (aka the proximal knuckles), their denervation causes these joints to become extended by the newly unopposed action of the extensor muscles of the forearm (namely the extensor digitorum and the extensor digiti minimi). However, if the lesion of the ulnar nerve occurs at the level of the wrist, the innervation of the medial half of the flexor digitorum profundus muscle (FDP), which is responsible for flexing the IP joints (the two distal joints of the fingers), is unaffected. It is the extension of the MCP joints coupled with the slight flexion of the IP joints that gives the hand the claw-like appearance.

Ulnar Paradox

The ulnar nerve also innervates the medial half of the FDP. If the ulnar nerve lesion occurs more proximally (closer to the elbow), the FDP may also be denervated. As a result, flexion of the IP joints is weakened, which reduces the claw-like appearance of the hand. (Instead, the 4th and 5th fingers are simply paralyzed in their fully extended position.) This is called the "ulnar paradox" because one would normally expect a more debilitating injury to result in a more deformed appearance.

Treatment

Surgery is sometimes performed.[4]

Other claw hands

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Median claw

Caused by median nerve lesions. The hand will show hyper-extension of the metacarpophalangeal joints (MCP) and flexion at the Interphalangeal (IP) joints of the 2nd and 3rd digits (index and middle). The pathogenesis is similar to that of ulnar clawing (loss of the relevant lumbricals and unopposed action of forearm flexors and extensors).

Dupuytren's contracture

Dupuytren's contracture is a deformity of the hand due to thickening and fibrosis of the palmar aponeurosis and eventual contracture of the 4th and 5th digits. Presenting as a small hard nodule in the base of the ring finger, it tends to affect the ring and little finger as puckering and adherence of the palmar aponeurosis to the skin. Eventually the MCP and IP joints of the 4th and 5th digits become permanently flexed. This claw appearance can be distinguished from an ulnar claw in that the MCP is flexed in Dupuytren’s but hyperextended in ulnar nerve injuries.

References

External links


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