What Are Hemivertebrae?
Hemivertebrae are spinal bones (vertebrae) that formed only partly before birth, leaving them shaped like a wedge or butterfly instead of a neat block. Because the spine is built from a stack of these bones, a wedge-shaped one tilts the spine at that point. In the tail this produces the corkscrew or “screw tail” look. In the back, especially the mid-spine, it can bend the spine and squeeze the spinal cord.
Many dogs with hemivertebrae never show any problem. A smaller group develop pain or weakness, usually while they are still growing.
Screw tail is a sign
A corkscrew tail is itself made of hemivertebrae. Dogs bred for that tail are much more likely to have malformed vertebrae elsewhere in the spine too.
Breeds at Risk
- Screw-tailed brachycephalic breeds: French Bulldogs, English Bulldogs, Pugs and Boston Terriers
- Occasionally German Shorthaired Pointers and other breeds, where it can be part of an inherited condition
See our guides to French Bulldog health problems and brachycephalic dog breeds for related conditions.
Signs to Watch For
Signs usually appear between about 5 and 9 months of age, while the spine is growing, though some dogs show them later in life.
- Wobbly or uncoordinated walking in the back legs
- Weakness, dragging or knuckling of the hind feet
- Back pain, a hunched posture or reluctance to jump
- A visible kink or curve in the back
- In severe cases, loss of bladder or bowel control, or paralysis
Diagnosis
X-rays show the wedge-shaped vertebrae, but because many dogs have them without symptoms, finding them on an X-ray does not prove they are the cause of a problem. A neurological exam and MRI or CT are used to see whether the spinal cord is actually compressed, and to rule out other causes such as intervertebral disc disease (IVDD), which these same breeds also get.
Treatment
- No symptoms: no treatment, just monitoring. Keeping your dog lean and using a harness instead of a collar reduces strain.
- Mild signs: rest, anti-inflammatory and pain medication, and physical therapy.
- Spinal cord compression with weakness: surgery to relieve pressure and stabilize the spine, performed by a veterinary neurologist or surgeon.
Outlook
Dogs with incidental hemivertebrae usually live normal lives. For dogs with spinal cord signs, the outlook depends on how severe the compression is and how quickly it is treated; dogs that can still walk generally do better after surgery than those that are already paralyzed.
Buying a Puppy
Ask breeders of screw-tailed breeds whether parents were screened with spinal X-rays, and consider how hemivertebrae and other inherited conditions are handled under congenital condition coverage in pet insurance before you enroll.
Frequently Asked Questions
Are hemivertebrae painful?
Usually not. They only cause pain or weakness when the abnormal shape bends the spine enough to press on the spinal cord.
Can hemivertebrae get worse?
Problems most often develop during growth. After a dog reaches maturity, new signs are less common, though they can appear with age or alongside disc disease.
Does a screw tail mean my dog will have back problems?
Not necessarily. Many screw-tailed dogs never have spinal symptoms, but they are at higher risk, so watch for hind-leg weakness.
Seeing wobbliness or back pain in a young Frenchie, Pug or Bulldog? Book an exam at a veterinary clinic near you.