|Classification and external resources|
Wrist drop, also known as radial nerve palsy, is a condition where a person cannot extend their wrist and it hangs flaccidly. To demonstrate wrist drop, hold your arm out in front of you with your forearm parallel to the floor. With the back of your hand facing the ceiling (i.e. pronated), let your hand hang limply so that your fingers point downward. A person with wrist drop would be unable to move from this position to one in which the fingers are pointing up towards the ceiling.
Anatomy of the forearm
In anatomical parlance, the forearm is the part of the body which extends from the elbow to the wrist and is not to be confused with the arm which extends from the shoulder to the elbow. The extensor muscles in the forearm are extensor carpi ulnaris, extensor digiti minimi, extensor digitorum, extensor indicis, extensor carpi radialis brevis, extensor carpi radialis longus. These extensor muscles are supplied by the posterior interosseous nerve, a branch of the radial nerve. Other muscles in the forearm also innervated by the radial nerve are supinator, extensor pollicis brevis, extensor pollicis longus, and abductor pollicis longus. Note that all these muscles are situated in the posterior half of the forearm (posterior when in the anatomical position). Also, brachioradialis, anconeus, triceps brachii, and extensor carpi radialis longus are all innervated by muscular branches of the radial nerve in the arm.
Wrist extension is achieved by muscles in the forearm contracting, pulling on tendons that attach distal to (beyond) the wrist. If the tendons, the muscles, or the nerves supplying these muscles, are not working as they should be, wrist drop may occur. The following situations may result in wrist drop:
Stab wounds to the chest at or below the clavicle may result in wrist drop. The radial nerve is the terminal branch of the posterior cord of the brachial plexus. A stab wound may damage the posterior cord and result in neurological deficits including an inability to abduct the shoulder beyond first 15 degrees, an inability to extend the forearm, reduced ability to supinate the hand, reduced ability to abduct the thumb and sensory loss to the posterior surface of the arm and hand.
Persistent injury to the nerve is also a common cause through either repetitive motion or by applying pressure externally along the route of the radial nerve as in the prolonged use of crutches or extended leaning on the elbows. For this reason radial nerve palsy is also sometimes referred to as crutch paralysis, Saturday Night Palsy (individual falls asleep with the back of their arm compressed by the back of a chair), or Honeymoon Palsy (one individual sleeps on the arm of another individual).
Radial nerve palsy can result from the now discredited practice of correcting a dislocated shoulder by putting a foot in the person's armpit and pulling on the arm in attempts to slide the humerus back into the glenoid cavity of the scapula.
1) Weakness of brachioradialis, wrist extension and finger flexion = radial nerve lesion (2) weakness of finger extension and radial deviation of the wrist on extension = posterior interossious nerve lesion (3) weakness of triceps, finger extensors and flexors = c7,8 lesion (4) generalised weakness of upper limb marked in deltoid, triceps, wrist extension and finger extension = corticospinal lesion
The workup for wrist drop frequently includes nerve conduction velocity studies to isolate and confirm the radial nerve as the source of the problem. Other screening tests include the inability to extend the thumb into a "Hitchhiker's sign". Plain films can help identify bone spurs and fractures that may have injured the nerve. Sometimes MRI imaging is required to differentiate subtle causes.
Initial management includes splinting of the wrist for support along with Chiropractic, Osteopathic medicine, Physiotherapy and Occupational Therapy. In some cases, surgical removal of bone spurs or other anatomical defects that may be impinging on the nerve might be warranted. If injury was the result of pressure from prolonged use of improperly fitted crutches or other similar mechanisms of injury, then the symptoms of wrist drop will most likely resolve spontaneously within 8–12 weeks.
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