The radial nerve is another of the nerves of the brachial plexus and originates from spinal cord segments C7-T2. Distal radial nerve paralysis results in inability of an animal to extend its carpus and digit. Proximal radial nerve paralysis is difficult to differentiate clinically from brachial plexus injury and prevents an animal from extending its elbow, carpus, and fetlock (metacarpophalangeal joint) to bear weight.
Etiology of Radial Nerve Injury in Cattle
The proximal radial nerve may be injured by stretching close to the brachial plexus, in which case the triceps muscles, as well as the extensors of the carpus and digits, may be compromised. The damage is frequently associated with casting an animal with ropes or with any situation in which the forelimb is accidentally restrained and the animal struggles violently to free itself. Distal radial nerve paralysis can result from prolonged recumbency in very heavy animals.
The distal radial nerve is vulnerable to injury in the musculospiral groove of the humerus, either from prolonged lateral recumbency on a tilt table or, less frequently, from fractures or deep soft tissue trauma.
Clinical Findings and Diagnosis of Radial Nerve Injury in Cattle
In proximal radial nerve paralysis and brachial plexus injury, the elbow drops, the carpus and fetlock are in partial flexion, and the limb is usually dragged. In the more commonly occurring distal radial nerve paralysis, because the triceps muscles remain functional, dropping of the elbow is minimal, and the animal can bear weight on the affected limb if the foot is placed directly under the animal. However, paresis affecting carpal and fetlock position is present, and the animal is unable to advance the limb.
Treatment of Radial Nerve Injury in Cattle
Rapid improvement of radial nerve paralysis can be expected in most cases with anti-inflammatory treatment. Patients should be confined in a generously bedded stall, and the fetlock should be protected with a bandage to prevent septic arthritis from damage to the skin over the fetlock. A cast up to the elbow is needed in severe cases to minimize trauma to the ventral aspect of the fetlock as the animal drags the forelimb around. Administration of anti-inflammatory drugs may be helpful, particularly in the first few days after the initial trauma. When the condition persists for ≥2 weeks, damage is likely permanent and the prognosis is poor.