French Bulldog hemivertebrae are malformed bones in the spine, and they are linked to the breed's short "screw" tail. Most Frenchies have at least one, and most never show any sign of it. A few develop weakness or a wobbly walk, and the malformations can raise the risk of disc disease. Here is what the screw tail and hemivertebrae mean for your dog, which symptoms matter and how vets diagnose them.

Do French Bulldogs have tails?

Yes. French Bulldogs are born with a naturally short tail; it is not cut or docked. The AKC breed standard describes it as "either straight or screwed (but not curly), short, hung low, thick root and fine tip."[4] So both a short straight tail and a kinked "corkscrew" tail fit the standard.

The short, kinked tail has a known genetic basis. A 2018 study found a variant in the DVL2 gene that was the strongest genetic match for screw tail. It is fixed in French Bulldogs and English Bulldogs (all dogs carry it) and present in 94% of Boston Terrier gene copies. The same variant travels with malformed vertebrae in the chest and tail.[1] In other words, the tail and the spine problems come from the same root.

What are hemivertebrae?

A hemivertebra literally means "half vertebra": one of the bones of the spine does not form completely.[3] Merck lists hemivertebrae alongside block vertebrae (fused bones) and butterfly vertebrae (split bones), and notes that hemivertebrae are "most common in screw-tailed dog breeds."[5]

Because the bone is only partly formed, the spine can bend at that point, most often into a hump called kyphosis.[3]

How common are French Bulldog hemivertebrae?

Very common. A 2017 study looked at CT scans of 62 French Bulldogs that had been scanned for unrelated reasons and had no neurological signs:[2]

  • 93.5% had at least one hemivertebra, and 79% had several.
  • The middle of the chest (the 9th and 10th thoracic vertebrae) was most often affected.
  • Only one French Bulldog in the study's clinical population had a malformation actually causing signs. Pugs were more often affected clinically.

Another study of the same issue found that, in French Bulldogs, the more severe the screw tail, the more severe the hemivertebrae in the chest tend to be.[6]

The Royal Veterinary College sums it up: in French Bulldogs, hemivertebrae with kyphosis usually do not cause signs, but they "should not be considered an innocent and benign condition." The curve slightly changes how these dogs walk and increases their risk of disc disease in the mid-back (IVDD), which is "by far the most common spinal disorder in French bulldogs."[3]

Hemivertebrae symptoms in French Bulldogs

When a malformation does press on the spinal cord, the RVC describes "progressive paresis and ataxia of the pelvic limbs" (gradually worsening weakness and wobbliness in the back legs), typically starting early in life.[7] In a French referral study of 343 French Bulldogs with neurological disease, 19 had a compressive vertebral malformation, and 17 of those were hemivertebrae, usually with a pronounced hump.[8] Watch for:

  • A young dog that walks more clumsily, crosses or drags its back feet, or scuffs its nails
  • Back legs that get weaker over weeks or months
  • A visible hump in the back
  • Loss of bladder or bowel control

Emergency: if your Frenchie suddenly cannot stand, drags its legs or seems to have no feeling in its back paws, go to an emergency vet now. In this breed that is more often a disc herniation than a hemivertebra, and both need fast imaging. See back pain and weak legs in French Bulldogs.

Diagnosis: hemivertebrae on X-ray, CT and MRI

Most vertebral malformations are visible on ordinary X-rays.[9] They are often found by chance: in one CT study, almost all French Bulldogs scanned for other reasons had at least one.[2] A malformation seen on imaging does not, by itself, call for treatment.[9]

  • CT shows bone shape in detail and helps a surgeon judge whether a defect can be corrected.[5]
  • MRI is used when a dog has neurological signs, to see whether and where the spinal cord is compressed.[9]

The hardest part is deciding whether a malformation is relevant. The RVC notes it is "challenging to differentiate between clinically relevant and irrelevant vertebral malformations,"[3] so a neurological exam matters as much as the images.

Hemivertebrae treatment and surgery

A dog with hemivertebrae and no signs needs no treatment, only sensible spine care: a lean body, a harness instead of a collar, ramps or steps for furniture and careful lifting. Our guide to French Bulldogs and stairs covers the evidence on jumping and stairs.

For dogs with progressive signs, the RVC reports that medical management alone "is unfortunately associated with a poor outcome," while surgery to stabilize the spine, with or without partial realignment, has given good results.[7] This is specialist surgery, usually planned from CT scans. Physical rehabilitation can help with strength and function.[9] Ask a board-certified veterinary neurologist or surgeon about the options for your dog.

Other French Bulldog tail problems

A tightly screwed tail often sits in a deep skin fold, the "tail pocket," which can trap moisture and get infected. Redness, smell or your dog scooting or licking the area are reasons to check it. Our guide to the French Bulldog tail pocket explains cleaning and when to see a vet. Researchers have also suggested breeding away from severe screw tails because of their link to spinal malformations.[6]

Sources and references

  1. Mansour TA, Lucot K, Konopelski SE, Dickinson PJ, Sturges BK, Vernau KL, et al. Whole genome variant association across 100 dogs identifies a frame shift mutation in DISHEVELLED 2 which contributes to Robinow-like syndrome in Bulldogs and related screw tail dog breeds. PLoS Genetics. 2018;14(12):e1007850. doi:10.1371/journal.pgen.1007850.
  2. Ryan R, Gutierrez-Quintana R, ter Haar G, De Decker S. Prevalence of thoracic vertebral malformations in French bulldogs, Pugs and English bulldogs with and without associated neurological deficits. The Veterinary Journal. 2017;221:25-29. doi:10.1016/j.tvjl.2017.01.018. Restricted access.
  3. Royal Veterinary College. Neurology [Internet]. RVC Research Focus: Brachycephaly; [date unknown] [cited 2026 Nov 3].
  4. American Kennel Club. Official Standard of the French Bulldog [Internet]. AKC; 2018 Apr 10 [cited 2026 Nov 3].
  5. Packer RA. Congenital and Inherited Disorders of the Nervous System in Dogs [Internet]. Merck Veterinary Manual (Dog Owners version); 2018 Feb [updated 2026 Jul; cited 2026 Nov 3].
  6. Broaddus KD. Congenital Malformations of the Lumbosacral Vertebral Column [Internet]. Clinician's Brief; 2020 Jan 16 [updated 2020 Feb; cited 2026 Nov 3].
  7. De Decker S. RVC offers new treatment for congenital vertebral malformations [Internet]. RVC Clinical Connections; 2018 [cited 2026 Nov 3].
  8. Mayousse V, Desquilbet L, Jeandel A, Blot S. Prevalence of neurological disorders in French bulldog: a retrospective study of 343 cases (2002–2016). BMC Veterinary Research. 2017;13(1):212. doi:10.1186/s12917-017-1132-2.
  9. Kerrigan S, Robinson D. Juvenile Orthopedic Disease in Dogs and Cats, Part 2: Congenital and Neonatal Orthopedic Diseases. Today's Veterinary Practice. 2016.