This is another injury that can result from major trauma, usually a motor vehicle injury. It can also occur when an animal gets one front foot caught while jumping a fence and is suspended in this position. The result is a severe traction injury to the limb that causes the nerve(s) supplying that limb to be stretched or to actually tear through completely. Unlike the rear limb, the front limb of an animal (just like our arm) is only joined to the body by muscles that attach to the major bones. The shoulder blade or scapula simply rests on the body and is kept in place by several large muscles. Any strong traction (or pull) on the front limb stretches these muscles along with the associated blood vessels and nerves that connect to the limb. If the pull is very severe the muscles are stretched and tremendous forces can be applied to the blood vessels and nerves. The weakest of all these structures are the nerve roots that attach right at the level of the spinal cord. When the nerve roots are stretched or torn the limb is immediately paralyzed. The exact extent of the injury depends on how many of the five nerve roots that supply the limb are injured and how severely. Diagnosis is indicated by the history of trauma and the characteristic findings of a neurological examination. After a severe injury the limb tends to drag on the ground although some animals retain the ability to flex their elbow and so can elevate the foot slightly as they walk on their three unaffected legs. Confirmation of the extent of the injury can be supplied by a CT scan combined with a myelogram or using an MRI.
In humans there are several surgeries that can be performed to try to regain function in the affected limb. However, although similar approaches are being evaluated in animals their recovery is protracted and it is unlikely that this approach will permit the limb to be used normally again. Furthermore the animal is still prone to several major complications during the recovery period such as not being able to protect a limb that it cannot feel and also development of unusual sensations that may cause the animal to mutilate its own foot.
After a brachial plexus injury the two main time points for recovery are 7-10 days after injury, when the bulk of the early swelling resolves, and then 4-6 weeks when there may be further improvement due to reversal of local nerve damage. Significant recovery is unlikely beyond 4-6 weeks for most animals although there are exceptions to these rules and each case is best assessed individually. Many animals do far better after the affected limb has been amputated rather than letting it drag around uselessly.
Figure 17-1: Diagrammatic representation of a brachial plexus injury that has caused a traction (strong pull) injury to one front limb. In this example the limb has been forced forward (white arrow) and therefore the most severe traction will be applied to the nerve roots (yellow arrows) at the tail-end of the brachial plexus. The result is that the nerve root at this end of the plexus is damaged and may even snap at the level of the spinal cord, with devastating consequences.
Figure 17-2: Rottweiler that has suffered the most severe type of brachial plexus avulsion injury. This is often a devastating injury, particularly for large breed of dog such as this.
The prognosis for recovery of limb function is poor in general for most animals with brachial plexus injury unless the neurological deficits are mild or improve rapidly. Complications include trauma to the foot caused by dragging it along the ground or, in some cases, because the animal will lick or even chew at the foot.
- Brachial Plexus Avulsion. REQUIRES LOGIN; FOR VETERINARIANS In Clinical Neurology in Small Animals: Localization, Diagnosis and Treatment. K.G. Braund.
ACVIM Proceedings Through VIN Require Login;
- Prognostic Factors For Functional Recovery In Dogs With Suspected Brachial Plexus Avulsion. D. Faissler. 2002 ACVIM Proceedings. Powered by VIN.