Ulnar nerve palsy can result in loss of sensory and motor function. This can occur after injury to any portion of the ulnar nerve. The ulnar nerve is the terminal branch of the medial cord (C8, T1). The ulnar nerve innervates the flexor carpi ulnaris after it passes through the cubital tunnel.
The nerve provides sensation over the medial half of the 4th finger and the entire 5th finger and the ulnar portion of the dorsal aspect of the hand.
Other muscles innervated by the ulnar nerve are the flexor digitorum profundus of the ring and small fingers and the following hand muscles:
When the ulnar nerve is injured, the muscles innervated by the nerve begin to weaken. This leads to an imbalance between the strong extrinsic muscles (i.e., extensor digitorum communis) and the weakened intrinsic muscles (i.e., interossei and lumbricals). This imbalance is characterized clinically by metacarpophalangeal (MCP) hyperextension and proximal interphalangeal (PIP) and distal interphalangeal (DIP) flexion. After carpal tunnel syndrome, entrapment of the ulnar nerve is the second most common neuropathy of the upper extremity.
The ulnar nerve can be entrapped at several sites that include the following:
Causes of claw hand can also be due to anything that may lead to ulnar nerve palsy. Ulnar nerve palsy can arise from a laceration anywhere along its course. Proximal injuries to the medial cord of the brachial plexus may also present with sensory loss distally. Ulnar nerve palsies can also be due to cubital tunnel syndrome and ulnar tunnel syndrome. These are compression neuropathies at the elbow and wrist. Another cause of ulnar nerve palsy may be due to a failure to splint the hand in an intrinsic-plus posture following a crush injury. There are a few systemic diseases which may also lead to ulnar nerve palsy. These include leprosy, syringomyelia, and Charcot-Marie-Tooth disease. However, these systemic diseases usually involve more than one nerve.
When a claw hand results, it is usually due to paralysis of the lumbricals.
Claw hand can be congenital or acquired. Men are more likely to acquire the condition than a woman, but the congenital form of claw hand is distributed evenly among men and women. There are no racial or ethnic preferences for claw hand.
Pathoanatomic components relate to the imbalance between the extrinsic and intrinsic muscles. Weakened intrinsic muscles lead to a loss of MCP flexion and a loss of interphalangeal (IP) extension. Strong extrinsic muscles will lead to an unopposed extension of the MCP joints. The flexor digitorum profundus and flexor digitorum superficialis muscles not innervated by the ulnar nerve remain strong and lead to unopposed flexion of the PIP and DIP joints.
The initial presentation will include a decrease in normal hand function.
The MCP joints will be hyperextended, and the IP joints flexed.
The second and third digits will not be as involved as the fourth and fifth digits with a true ulnar nerve palsy. This is because the median nerve innervates the lumbricals involving the second and third digits, and the ulnar nerve innervates the lumbricals involving the fourth and fifth digits.
The patient may also exhibit functional weakness while attempting a grasp, grip, or pinch.
A provocative test for claw hand is bringing the MCP joints into flexion. This will correct the DIP and PIP joint deformities.
Several other specific tests for ulnar nerve palsy include:
Exercises that strengthen the interosseous muscles and lumbricals are recommended. The individual should be taught to exercise each finger and thumb in abduction and adduction motion while the hand is pronated. In addition, the MCP and ICP joints should be exercised and over time the interosseous and lumbricals will gain strength.
The majority of cases will need operative management in the form of contracture release and passive tenodesis versus active tendon transfer. This treatment is reserved for those patients with a progressive deformity that is affecting their quality of life. The goal is to prevent lasting MCP joint hyperextension.
Differential diagnosis of a claw hand should include:
The prognosis depends on the type and extent of nerve injury. For mild nerve injury recovery is possible but if the nerve was transected, recovery is rare. Even those who recover may require prolonged hand rehabilitation and may never regain full strength of the hand muscles. Poor prognostic factors include:
Some studies do not show much improvement even after transposition of the ulnar nerve.
A very experienced hand therapist plays a vital role in the postoperative care of tendon transfers for ulnar nerve palsy. Protecting the transfers with custom splints while mobilizing uninvolved joints requires strict adherence to postoperative protocols. Following most procedures, the hand is immobilized for 3 to 4 weeks, followed by a blocking splint to allow movement within the restraints of the splint for the next 3 to 4 weeks. Passive exercises are started at 6 weeks and strengthening at 8 weeks for the adductorplasty and 10 to 12 weeks for the intrinsic tendon transfers.
The patient should be made aware of the prognosis and the need for regular physiotherapy, where indicated.
When patients present with a claw hand, an interprofessional team that includes a hand surgeon, neurologist, neurosurgeon, physical therapist, emergency department physician, and nurse practitioner should be involved in the diagnosis and management. Because there are several causes of a claw hand the initial referral should be to the neurologist. The treatment depends on the cause and extent of nerve injury.
The treatment depends on the acuteness of the condition and severity of the injury. Physical and occupational therapy is necessary for all individuals.
Extensive rehabilitation is required and patients should be urged to be compliant with treatment. Other comorbidities like diabetes should be treated and the pharmacist should urge the patient to discontinue smoking and abstain from alcohol. Since many patients do develop anxiety and depression, a consult with a mental health nurse is recommended. The occupational and physical therapists should continue with exercises that strengthen the hand muscles. Close communication with the team is highly recommended to ensure good outcomes.
The prognosis for most patients is guarded.
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