Median Nerve Injury

INTRODUCTION:

The median nerve is formed from parts of the medial and lateral cords of the brachial plexus, and continues down the arm to enter the forearm with the brachial artery

In the upper arm, median nerve has no motor innervations, but it gives vascular branches to the wall of the brachial artery (sympathetic fibers). In the forearm, it innervates most of the flexors in the aforearm except flexor carpi ulnaris and the medial two digits of flexor digitorum profundus, which are supplied by the nerve.

CLINICAL FEATURES:

-signs of a median nerve lesion include weak pronation of the forearm, weak flexion & radial deviation of wrist, with thenar atrophy & inability to oppose or flex the thumb

– sensory distribution includes thumb, radial 2 1/2 fingers, and corresponding portion of palm.
– with intact nerve, thumb can be pronated, lining up nails at or near 180 deg;
– with median nerve palsy, thumb can’t be pronated & nail is < 100 deg;

Injury of median nerve at different levels cause different syndromes.

  • Injury of this nerve at a level above elbow joint results in loss of pronation and a decrease in flexion of the hand at the wrist joint.
  • In the hand, thenar muscles are paralysed and atrophy in time. Opposition and flexion movements of thumb are lost, and thumb and index finger are arrested in adduction and hyperextension position. This appearance of the hand is collectively referred as ape hand deformity.

In addition, in palmar side of the hand sensation of lateral part of hand, first three fingers and lateral half of the fourth finger and in dorsal side sensation of distal ⅓ portions of first three fingers and lateral half of distal portion of fourth finger is lost.

Causes

Dysfunction of one nerve group, such as the distal median nerve, is called mononeuropathy. Mononeuropathy means there is a local cause of the nerve damage, although occasionally systemic (body-wide) disorders may cause isolated nerve damage (for example, mononeuritis multiplex).

Distal median nerve dysfunction occurs when the nerve is inflamed, trapped, or injured by trauma. Trapping (entrapment) involves pressure on the nerve where it passes through a narrow area. Wrist fractures may injure the median nerve directly or may increase the risk for trapping a nerve later on.

The nerve can also be compressed at the wrist by tendonitis, arthritis, or conditions that affect connective tissue or cause deposits in the tissues (such as multiple myeloma, pregnancy, acromegaly, and hypothyroidism). These mechanical factors may cause nerve disease, blocking blood flow to the area.

Symptoms

Sensation changes of the thumb and first 2 fingers

Decreased sensation

Burning sensationor tingling

Waking up at night with wrist or hand pain (may be severe)

Weakness of the hand

Dropping things

Difficulty grasping objects

 

Diagnostic Tests

Pen test:- patient is unable to touch the pen due to the loss of action of abductor pollicis brevis.

Pointing index or Oschners clasp test:- when both the hands are clasped together, index and middle fingers, fail to flex due to the loss of action of long finger flexors of the index and middle fingers which are supplied by the median nerve.

Benediction test :- for the same reason as above patient is unable to flex the index and middle finger on lifting the hand 9 this is the position –a clergyman uses to bless the couple during marriage.Hence called benediction test)

Treatment:

At the Arm Level

• Incision between biceps and brachialis over the course of the brachial artery. The medial antebrachial cutaneous may be encountered, but it is smaller than the median.

Elbow and Forearm Level

• S-shaped incision from above the flexor crease medial to biceps, across the crese, and downward. Will identify the nerve as it goes under the lacertus fibrosus and proximal to the pronator teres under which it dives.

Hand

• Main issue is to miss the thenar recurrent branch of the median nerve. The origin is quite variable. Palmar incision should thus be placed on the ulnar aspect of the nerve.

Kindly contact PHYSIOLINE for further consultation and rehabilitation