Wrist drop, also known as radial nerve palsy, is a condition where a person cannot extend their wrist and it hangs flaccidly.
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.
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.
- 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
- Weakness of brachioradialis, wrist extension and finger flexion = radial nerve lesion
- Weakness of finger extension and radial deviation of the wrist on extension = posterior interossious nerve lesion
- Weakness of triceps, finger extensors and flexors c7,8 lesion
- Generalised weakness of upper limb marked in deltoid, triceps, wrist extension and finger extension corticospinal lesion