Wrist drop - #medical article #anatomy

paralysis of the muscles which normally raise the hand at the wrist and extend the fingers, typically caused by nerve damage.

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.

Causes

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.

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.

Wrist drop is also associated with lead poisoning because of the effect of lead on the radial nerve.^[1]

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.^[2]

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

Diagnosis

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".^[3]Plain films can help identify bone spurs and fractures that may have injured the nerve. Sometimes MRI imaging is required to differentiate subtle causes.

Treatment

Initial management includes splinting of the wrist for support along with Osteopathy, 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.^[4]