Hemivertebra is a partially formed vertebrae.
Hemivertebrae happen when the vertebrae of the canine spine are congenitally deformed so as to fuse or otherwise develop abnormally in a manner that creates a twisting wedge in what should be a very straight spine. A deformity like this in the bony spine can mean a twisting in the spinal cord as well and, potentially, a compression of this exceedingly delicate central nervous system structure.
Luckily, most dogs are never adversely affected by this defect. In fact, this disease is typically diagnosed as an incidental finding and clinical signs of disease seldom become evident.
Hemivertebrae are responsible for the characteristic “screw tail” of bulldogs, pugs and other dog breeds for which the curled tail is considered a requisite trait. In the spinal cord-less tail, however, several defective vertebrae in a row do not present a problem. In some dogs, however, one or more vertebrae other than in the tail may be affected.
Symptoms and Identification
If signs should appear as a result of hemivertebrae, they’ll be related to excess pressure on the spinal cord as a result of compression in the region of the mid-thoracic spine (roughly in the middle of the back).
Diagnosis of hemivertebrae is made by taking simple X-rays. Signs of related disease, however, must be diagnosed by employing more sophisticated imaging studies to demonstrate that compression of the spinal cord is taking place as a result of the vertebrae.
Weakness of the hind limbs, fecal incontinence and urinary incontinence are most typical. Most symptoms will appear in puppyhood, worsening at first until reaching a stable plateau once the vertebrae stop growing.
Rest and anti-inflammatory drugs tend to help dogs only mildly affected by problems associated with hemivertebrae-associated spinal cord compression. Moderate to severely affected patients tend to require surgery called a hemilaminectomy to relieve the compression on the spinal cord in the location of the abnormal vertebra(e).
In dogs with “screw tails” for which the trait is part of the breed standard, carefully removing those dogs with any evidence of non-tail hemivertebrae from the breeding pool (even when they are not clinically affected) is absolutely necessary.