In a dog that has been hit by a car, what injury is suggested by a dropped elbow and absence of sensation on neurological examination?

The indication of a dropped elbow and absence of sensation on neurological examination strongly points to brachial plexus avulsion. This condition occurs when there is damage to the nerves of the brachial plexus, a network of nerves that supplies the forelimb. In a dog that has been hit by a car, the force of the impact can lead to traction or excessive force that results in the avulsion of these nerves from the spinal cord.

A dropped elbow typically occurs due to paralysis of the muscles that extend the elbow, which are innervated by branches of the brachial plexus. Absence of sensation accompanies this condition, as the sensory nerves that provide feeling to the affected area are also compromised.

In contrast, a humeral fracture or shoulder dislocation may cause pain and altered mobility, but they do not exclusively lead to a dropped elbow or sensory deficits linked to nerve damage. Radial nerve damage could contribute to a dropped elbow, but it would not account for the absence of sensation at the level of the brachial plexus. This helps to clarify why the specific presentation of dropped elbow and loss of sensation aligns most closely with brachial plexus avulsion.