Write 2 features each for differential diagnosis of right wrist drop in a 10 yr old boy with respect to anatomical location of pathology ?
A 1 INTRODUCTION
1 - Wrist drop (radial nerve or musculospiral nerve palsy, and colloquially as crutch paralysis, Saturday night palsy or honeymoon palsy) is a medical condition in which the wrist and the fingers cannot extend at the metacarpophalangeal joints.
2 - The wrist remains partially flexed due to an opposing action of flexor muscles of the forearm. As a result, the extensor muscles in the posterior compartment remain paralyzed.
RELEVANT ANATOMY
1 The forearm is the part of the body that extends from the elbow to the wrist and is not to be confused with the arm, which extends from the shoulder to the elbow.
2 The extensor muscles in the forearm are the extensor carpi ulnaris, extensor digiti minimi, extensor digitorum, extensor indicis, extensor carpi radialis brevis, and extensor carpi radialis longus.
3 These extensor muscles are supplied by the posterior interosseous nerve, a branch of the radial nerve.
4 v imp Other muscles in the forearm that are innervated by the radial nerve are the supinator, extensor pollicis brevis, extensor pollicis longus and abductor pollicis longus. All of these muscles are situated in the posterior half of the forearm (posterior is when it is in its standard anatomical position).
5 Also, the brachioradialis, anconeus, triceps brachii and extensor carpi radialis longus are all innervated by muscular branches of the radial nerve in the arm.
MECHANISM OF INJURY
1 The mechanism of radial neuropathy is such that it can cause focal demyelination and axonalproblems/degeneration (which is nerve fiber reaction to insult, and therefore axon death occurs).
A ) These would be caused via laceration or compression of the nerve in question.
TYPES OF WRIST DROP
Types of wrist drop are distinguished by the nerves affected -
A ) Weakness of brachioradialis, wrist extension and finger flexion = radial nerve lesion
B ) Weakness of finger extension and radial deviation of the wrist on extension = posterior interosseous nerve lesion
C )Weakness of triceps, finger extensors and flexors = c7,8 lesion
D ) General weakness of upper limb marked in deltoid, triceps, wrist extension and finger extension = corticospinal lesion
FEATURES EACH FOR DIFFERENTIAL DIAGNOSIS
The following situations may result in wrist drop -
A ) Stab wounds to the chest at or below the clavicle–The radial nerve is the terminal branch of the posterior cord of the brachial plexus.
1 - A stab wound may damage the posterior cord and result in neurological deficits -
A ) including an inability to abduct the shoulder beyond the first 15 degrees
B ) an inability to extend the forearm
C ) reduced ability to supinate the hand
D ) reduced ability to abduct the thumb
E ) sensory loss to the posterior surface of the arm and hand.
B ) Broken humerus–The radial nerve can be damaged if the humerus (the bone of the arm) is broken because it runs through the radial groove on the lateral border of this bone along with the deep brachial artery.
Features -
1 The fracture is typically accompanied by a discoloration of the skin at the site of the fracture.
2 Displaced fractures of the humerus shaft will often cause deformity and a shortening of the length of the upper arm.
3 Distal fractures may also cause deformity, and they typically limit the ability to flex the elbow.