Here is a physiotherapist's guide on the assessment and management of ulnar nerve injury. The image of the blessing hand is taken from the iconography of the Christian period and today is used in the context of musculoskeletal physiotherapy, to explain some particular conditions linked to neuropathies of the upper limb.
When we talk about the blessing hand we refer to the position of the hand during the act of blessing: the first finger relaxed, the second and third fingers extended and the fourth and fifth fingers in an attitude of flexion of the distal and proximal interphalangeal joints and extension of the joints metacarpophalangeal.
But what is the problem underlying this particular condition?
In various textbooks it is also common to find expressions such as “Greek-style blessing hand” or “Latin-style blessing hand” as the position of the hand recalls respectively the Greek letter χ (“who”), or the Latin letter letters used to indicate Christ. You can also often find the expressions “claw hand” or “old hand” sign (1).
In the literature, for several years there has been debate about attributing the sign of the blessing hand to a lesion of the ulnar nerve or the median nerve, the two nerves that mainly compete for the palmar territory of the hand.
Ulnar nerve injury
To date, the literature agrees in attributing this particular condition to an ulnar neuropathy, but it is not entirely incorrect to use this expression even for an advanced case of median nerve neuropathy (1).
The ulnar nerve arises from the medial cord of the brachial plexus, which incorporates the C8–T1 nerve roots. When it reaches the forearm it gives rise to the motor branches that innervate the flexor carpi ulnaris and the medial half of the flexor digitorum profundus (2).
In the hand, the ulnar nerve innervates the hypothenar muscles, the lumbrical muscles of the fourth and fifth fingers and the interosseous muscles.
In the presence of a nerve injury
The blessing hand sign generally appears when asked to open the hand. Due to the loss of function of the medial lumbrical muscles, in fact, the metacarpophalangeal joints of the fourth and fifth fingers will be in extension, while the interphalangeal joints will be in flexion.
- If the lesion were to affect the median nerve, the flexors of the second and third fingers would suffer loss of function.
- When asked to make a fist, therefore, a patient with advanced damage to the median nerve would find it difficult to close the hand completely, leaving the first two fingers half open.
The clinical sign is similar
But the sites of injury and the functional demands that evoke this sign are different (3).
Peripheral neuropathies are accompanied by symptoms of progressive impairment of nerve functioning, secondary to chronic and mechanical damage to the nerve itself. In the case of the ulnar nerve, the most common site of compromise is Guyon's canal, from which the syndrome of the same name derives.
The anatomical borders of Guyon's lodge are given by the pisiform bone, hook of the hamate, transverse carpal ligament and pisiform-hamate ligament.
The symptoms of an initial phase
Are given by sensory deficits and wrist pain, mainly during the nocturnal period, paresthesia and hypoesthesia of the 4th and 5th fingers, while in a late phase we have mobility deficits and hypotrophy of the muscles belonging to the nerve ulnar (4).
The clinical picture can vary based on the site of compression and, generally, three different types of entrapment are distinguished:
Froment Sign is recognized by increased flexion of the thumb.
- in type I the compression is internal or proximal to the canal and presents all the symptoms described above;
- in type II there is greater impairment of the deep motor branch at the level of the hamate hook;
- in type III, only the sensory branch that innervates the ulnar area of the palm, the 5th finger and the ulnar side of the 4th finger is compromised (5).
Other authors further divide the lesions of the motor branch into types IV and V with greater involvement of the first dorsal interosseous and the adductor of the thumb (6).
The Froment sign and the Wartenberg sign
On physical examination it is also possible to observe two other signs indicative of an ulnar nerve lesion.
Froment's sign is due to a weakness of the adductor muscle of the thumb and is elicited when the patient is asked to squeeze a sheet of paper between thumb and index finger. Since the thumb cannot be adducted, the patient will flex the distal phalanx.
Using the long flexor muscle of the thumb innervated by the median nerve.
On the left a grip with positive Froment's sign, on the right a normal grip of the sheet.
The Wartenberg sign is due to the weakness of the third palmar interosseous, with inability to adduct the fifth finger. It may happen that the patient reports in his anamnesis that the little finger remains “outside” when putting a hand in his pocket or putting a hand in his bag (7).