Ulnar Claw vs Hand of Benediction

Author: Oliver Jones

Last modified: April 12, 2014

The ulnar claw and hand of benediction are two characteristic signs of peripheral nerve damage. Although they look largely the same, the underlying pathology is very different.

This article will look at the anatomy and functions of the ulnar and median nerves. We shall apply this knowledge to explain how these two characteristic clinical signs are produced.


Ulnar Claw

The ulnar claw is a deformity that is seen in long standing ulnar nerve damage at the wrist. It affects the little and ring fingers of the hand. These fingers are hyperextended at the metacarpophalangeal (MCP) joint, and flexed at both interphalangeal (IP) joints.

To explain why this occurs, we need to consider the muscles that are affected by an ulnar nerve lesion at the wrist:

  • Medial two lumbricals: Flexes at the MCP joints and extends at the IP joints of the little and ring fingers.
  • Interossei: Abducts and adducts the fingers.
  • Hypothenar muscles: Flexes, adducts, and opposes the little finger.
  • Adductor pollicis: Adducts the thumb.
Fig 1.6 - Ulnar claw hand. A deformity resulting from damage to the ulnar nerve at the elbow.

Fig 1.6 – Ulnar claw hand. A deformity resulting from damage to the ulnar nerve at the elbow.

In the ulnar claw, the important muscles to consider are the medial lumbricals. If these muscles are paralysed, there is a loss of flexion at the MCP joints, and a loss of extension at the IP joints. This leads to an imbalance between the intrinsic and extrinsic muscles of the hand – producing the claw deformity:

  • The MCP joints are hyperextended due to unopposed extension from the long extensor muscles in the posterior compartment of the forearm.
  • The IP joints are flexed due to unopposed flexion from the long flexor muscles in the anterior compartment of the arm. The extensor muscles cannot extend at the IP joints as their energy is dissipated in hyperextending the MCP joints.

The ulnar claw only occurs in the little and ring fingers, as the lateral two lumbricals are innervated by the median nerve.

Ulnar Paradox

The ulnar claw is a deformity produced by an ulnar nerve lesion at the wrist. We shall now look at what happens if the ulnar nerve is damaged more proximally – at the elbow.

In a high ulnar nerve injury, some muscles in the anterior forearm are paralysed (in addition to the hand muscles mentioned above):

  • Medial half of flexor digitorum profundus: Flexes at the distal IP joints of the ring and little fingers.
  • Flexor carpi ulnaris: Flexes and adducts the wrist.

The ulnar claw will develop as before, but with one key difference. The flexor digitorum profundus is paralysed, and there will not be any flexion at the distal IP joints of the ring and little fingers. Now the ulnar claw only consists of hyperextension at the MCP joints and flexion at the proximal IP joints. This produces a much less evident claw hand.

This is known as the ‘ulnar paradox‘ – you would expect a more debilitating injury to produce a more pronounced deformity, but in fact the opposite occurs.


Hand of Benediction

The hand of benediction occurs as a result of median nerve damage at the elbow. In contrast to the ulnar claw, which is produced spontaneously, the hand of benediction is only apparent if the patient is asked to make a fist.

Fig 1.1 - Hand of Benediction. Result of median nerve damage

Fig 1.1 – Hand of Benediction. Result of median nerve damage

To explain how the hand of benediction is produced, we need to consider the muscles affected if the median nerve is lesioned at the elbow:

  • Long flexors in the anterior compartment of the arm (except the medial half of the flexor digitorum profundus and the flexor carpi ulnaris).
  • Lateral two lumbricals: Flexes at the MCP joints and extends at the IP joints of the index and middle fingers.

If the patient is asked to make a fist, they will be able to flex the little and ring fingers. This action is performed by the medial half of the flexor digitorum profundus and the medial two lumbricals.

The patient will not be able to flex the index and middle fingers. Thus, the patient displays a claw shape, where the little and ring fingers and flexed, the index and middle fingers extended.


Contrasting Ulnar Claw and Hand of Benediction

At a first glance, distinguishing between the two can be difficult, but there are numerous differences between ulnar claw and hand of benediction.

Table 1.0 - Differences between the ulnar claw and hand of benediction

Table 1.0 – Differences between the ulnar claw and hand of benediction