Distal radial paralysis results in an inability to extend the carpus and digit. Proximal radial paralysis prevents the animal from extending the elbow, carpus, and fetlock to bear weight.
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. Either distal or proximal radial 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 fractures or deep, soft-tissue trauma. A lesion of the nerve proximal to the sulcus for the brachial muscle causes proximal radial paralysis.
In proximal radial paralysis, the elbow drops, the carpus and fetlock are in partial flexion, and the limb is usually dragged. In distal radial paralysis, because the triceps muscles remain functional, dropping of the elbow is minimal. However, paresis affecting carpal and fetlock position is present.
Rapid improvement can be expected in most cases. Animals should be confined in a generously bedded stall. Anti-inflammatory drugs may be helpful, particularly in the early hours after the initial trauma. If skin sensation in the forelimb has been completely lost, the prognosis is guarded. When the condition persists for ≥2 wk, damage is likely permanent and the prognosis is grave.