The waiter's tip injury occurs with damage to the superior trunk of the brachial plexus (C5-C6). The superior trunk can be damaged by stab wounds or when the head and trunk is separated from the shoulder during falls. The major nerves that would be damaged by this injury are the suprascapular, musculocutaneous, and axillary nerves. The major muscle affected by disruption of these nerves are the deltoid (abductor of the shoulder), supraspinatus (abductor of the shoulder), infraspinatus (lateral rotator of the shoulder), teres minor (lateral rotator of shoulder), biceps brachii (supinator and flexor of forearm), and brachialis (flexor of elbow). Injury to these muscles results in a position called the waiter's tip. As shown in the diagram below the limb hangs limply by the side, is medially rotated, with the forearm pronated due to loss of the supinating action of the biceps brachii.
- Big Snell, pg 480
Claw Hand results from an injury to the inferior trunk of the brachial plexus (C8-T1). This injury results from excessive abduction of the arm such as when a person grasps onto something to prevent falling. The nerve fibers from this trunk run in the median and ulnar nerve and supply all the small muscles of the hand (lumbricals and interossei). Paralysis of these intrinsic muscles of the hand causes the fingers to assume the "claw hand" position demonstrated below. This position is caused by the unopposed action of the extensor digitorum (which extends the metacarpophalangeal joints) and the flexor digitorum superficialis and profundus (which flex the fingers). Normally, these muscles are opposed by the lumbricals and the interosseus muscles.
- Lecture Notes
Wrist drop is caused by injury to the posterior cord and the radial nerve in the axilla. This injury can be caused by ill-fitting crutches or a downward dislocation of the humerus. Disruption of the radial nerve results in paralysis of the triceps, anconeus, and extensor muscles of the wrist. The person will be unable to extend the elbow, wrist, or digits. The resulting position of the upper limb, demonstrated in the diagram below, is called wrist drop.
- Big Snell, pg 484
Injury to the median nerve within the elbow region results in some characteristic deficiencies (which you should be able to predict by understanding the distribution of the nerve). The arm muscles are not affected because none of them are supplied by the median. However, pronation of the forearm, flexion of the wrist and digits, and movement of the thumb are severely affected. The pronator muscles of the forearm and the long flexors of the wrist and fingers will be paralyzed, except for the flexor carpi ulnaris and medial half of the flexor digitorum profundus. When the patient tries to make a fist, as shown below, the index and to a lesser extent middle fingers remain straight, while the ring and little finger flex.
- Big Snell, pg 486
The axillary nerve may be injured by fracture of the humerus or dislocation of the shoulder. Following severance of the axillary nerve, the deltoid muscle is paralyzed and atrophies.
The ulnar nerve can be damaged when the medial epicondyle of the humerus is damaged (like when you hit your funny bone). Ulnar nerve damage leads to paralysis of the flexor carpi ulnaris, medial half of the flexor digitorum profundus, and all of the small muscles of the hand except for the thenar muscles and the first two lumbricals. With paralysis of these muscles, a person is unable to flex the ring or little finger, adduct or abduct the digits, or adduct the thumb. The hand assumes the characteristic position shown below. The metacarpophalangeal joints become hyperextended due to paralysis of the lumbricals and interosseus muscles, which usually flex these joints. The interphalangeal joints are flexed- also due to paralysis of the lumbrical and interosseus muscles , which usually extend the joints. This condition is most marked in the medial two digits. In addition, there will be wasting of the hypothenar eminence and hollowing between the metacarpal bones due to atrophy of the hypothenar and interossei muscles.
- Big Snell, pg 488
Winged scapula results from injury to the long thoracic nerve, a supraclavicular branch (C5-C7) of the brachial plexus. This nerve to the serratus anterior lies on the medial wall of the axilla. The nerve may be injured by a stab wound, weight lifting, or a mastectomy. The paralyzed serratus anterior can no longer keep the scapula against the chest wall, which leads to the winged position shown below.
- Big Snell, pg 481
