Ulnar claw
An ulnar claw, also known as claw hand, is an abnormal hand position that develops due to a problem with the ulnar nerve. A hand in ulnar claw position will have the 4th and 5th fingers drawn towards the back of the hand at the first knuckle and curled towards the palm at the second and third knuckles.
Some sources refer to the ulnar claw as a "hand of benediction"[1]. However, the term "hand of benediction" more commonly refers to a similar hand position which is caused by damage to the median nerve[2][3] and is only present when the patient is asked to make a fist.
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) [4]. The clawing will become most obvious when the person is asked to straighten their fingers.
Patients exhibiting an ulnar claw are also very frequently unable to spread (abduct) or pull together (adduct) the fingers against resistance. This occurs because the ulnar nerve also innervates the palmar and dorsal interossei of the hand. Patients with this deficit will become increasingly easy to identify over time as the paralyzed first dorsal interosseous muscle atrophies, leaving a prominent hollowing between the thumb and forefinger.
Pathogenesis
An ulnar claw may follow an ulnar nerve lesion[5] 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.[6] (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.[7]
Other claw hands
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), and a median claw hand will appear almost identical to an ulnar claw when the patient with a median claw is asked to make a fist.
The following signs may be used to distinguish median nerve clawing from ulnar nerve clawing clinically.
| Ulnar nerve | Median nerve |
|---|---|
| Deficit is primarily in 4th and 5th fingers | Deficit is primarily in 2nd and 3rd fingers. |
| Deficit is most prominent at rest and when the patient is asked to extend his fingers. | Deficit is most prominent when the patient is asked to make a fist. |
| Often accompanied by inability to abduct or adduct the 2nd, 3rd, 4th, and 5th finger. | Often accompanied by difficulty opposing the thumb. |
| Often accompanied by apparent atrophy of the first dorsal interosseous muscle of the hand | Often accompanied by wasting of muscles of the thenar eminence |
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.
Klumpke paralysis
A claw hand can result of injuries to the inferior brachial plexus (C8 - T1). The condition may arises from the limb being suddenly pulled upward. For example, Klumpke paralysis can occur from excessive pulling of the infant's forelimb during parturition.
References
- ^ http://www.tabers.com/tabersonline/ub/view/Tabers/143428/26/benediction_hand
- ^ http://cpmcnet.columbia.edu/student/ssn/anatomy/brachial_plexus.pdf
- ^ http://cme.medscape.com/viewarticle/527751_8
- ^ Wheeless' Textbook of Orthopaedics - Ulnar Nerve
- ^ Neiman R, Maiocco B, Deeney VF (1998). "Ulnar nerve injury after closed forearm fractures in children". J Pediatr Orthop. 18 (5): 683–5. doi:10.1097/00004694-199809000-00026. PMID 9746426.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ http://www.orthoteers.org/content/documents/Exam_hand.pdf
- ^ Taylor NL, Raj AD, Dick HM, Solomon S (2004). "The correction of ulnar claw fingers: a follow-up study comparing the extensor-to-flexor with the palmaris longus 4-tailed tendon transfer in patients with leprosy". J Hand Surg [Am]. 29 (4): 595–604. doi:10.1016/j.jhsa.2004.03.006. PMID 15249082.
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