It may be injured in the axilla or in the radial groove. Its main branch, the posterior interosseous nerve may be injured at the elbow.
Causes-
1. In the axilla-
- Crutch palsy.
- Fractures and dislocations of upper end of the humerus, or by attempts at their reduction.
- Rarely by pressure of a new growth.
2. In the radial groove-
- Pressure of the arm on the edge of the operating table or on the edge over handle of chair or footpath after a heavy slip following excessive drink may bring about injury to the radial nerve at this site.
- Prolonged application of a tourniquet or ill applied plaster of the middle of the arm.
- Fracture of the shaft of the humerus.
- During operation on the humerus due to non-united fracture.
- Intramuscular injection of drugs may rarely injure radial nerve.
3. At the elbow-
- Fracture of the neck of the radius or dislocation of the radius.
- During operation of excision of the head of the radius.
Symptoms-
1. When injured in the axilla-
- Motor paralysis.
- Motor paralysis of triceps muscle, which causes inability to extend the forearm against resistance.
- Extensors of the wrist become paralyzed which causes wrist drop.
- Extensors of the all joints of the thumb are paralyzed. So extension of thumb is not possible in radial nerve injury.
- The supinator and brachioradialis are paralysed. But supination is completely lost when the forearm is extended.
- Sensory loss- In radial nerve injury in axilla anesthesia will be present on the dorsum of the arm, forearm and back of the hand.
- Trophic changes.
2. Injury in the radial groove-
- Motor paralysis.
- Sensory loss- In the radial nerve injury at the radial groove anesthesia is limited to a patch on the back of the hand and radial side of the thumb and the adjoining part of the thenar eminence, the medial side of the thumb and the adjoining sides of the index middle and lateral side of the ring finger. There is also anesthesia on the back of fingers up to the proximal interphalangeal joints except in the thumb where it reaches up to the nail.
- Trophic changes.
3. At the elbow- Posterior interosseous nerve is mainly injured. Motor paralysis and sensory loss.