If you have done any research on French Bulldog health before signing a purchase contract, you have almost certainly heard about BOAS and intervertebral disc disease. Breeders mention them, vet techs mention them, and rescue sites publish warnings about them. What almost no one tells buyers is that the spinal condition most likely to be present in their dog is neither of those. Hemivertebrae - malformed vertebrae present from birth - affect somewhere between 78 and 97 percent of French Bulldogs, depending on the study. Yet the condition rarely gets more than a passing paragraph in consumer-facing health content, and in many cases nothing at all. This guide covers it fully, from the underlying genetics to what to watch for in a puppy's first months to what responsible breeders actually do about it before they breed.
Not the Same as IVDD: The Congenital-vs-Degenerative Divide
Hemivertebrae and intervertebral disc disease are both spinal conditions in French Bulldogs. That is where the similarity ends. Understanding the difference before reading anything else about either condition will save you from a great deal of confusion.
Hemivertebrae are congenital malformations. The vertebrae that form during fetal development do not grow into normal rectangular blocks. Instead, one side develops more than the other, or the two halves fail to fuse, or ventral tissue is simply absent. These abnormalities are present at birth, visible on x-ray from the start, and do not progress the way a degenerative disease does.
IVDD is a degenerative disc disease. In chondrodystrophic breeds like French Bulldogs, the discs between vertebrae undergo premature calcification, lose their shock-absorbing capacity, and eventually herniate - compressing the spinal cord. Clinical signs from IVDD in French Bulldogs typically first appear in young to middle adulthood, with a median age of approximately four years, though the range varies considerably - not in puppyhood.
A puppy can be born with multiple hemivertebrae and remain neurologically normal for life. A dog with no hemivertebrae can still develop IVDD. These are independent problems with different mechanisms - though they can interact badly when both are present in the same spine.
Knowing this distinction matters before everything else. The two conditions require different monitoring windows, different imaging strategies, and different conversations with a veterinary neurologist.
The Screw-Tail Connection: Why Frenchies Are Built This Way
The same genetic mutation responsible for the French Bulldog's corkscrew tail also produces hemivertebrae throughout the rest of the spine. Current research has identified a frameshift mutation in the DVL2 (DISHEVELLED 2) gene - part of the WNT cell-signaling pathway - as the likely driver of vertebral malformation in screw-tail breeds including French Bulldogs, though the precise genetics remain an active area of study. The tail vertebrae are simply the most visible expression of a process happening along the entire spinal column.
This is not a trivial footnote. It means that every French Bulldog bred for the physical traits associated with breed type - the compact frame, the corkscrew tail - carries an elevated baseline risk of vertebral malformation. Breeding selection for appearance has not been consistently coupled with selection against vertebral abnormality, which is part of why prevalence figures remain so high.
Heritability estimates for hemivertebrae are substantial. Published data using an animal-threshold model places heritability at 0.58 for the number of abnormal vertebrae and 0.53 for their severity grade. Numbers in that range mean selective breeding away from severe hemivertebrae is genuinely feasible over generations. Breeders who use spine x-rays as a selection tool are working with a condition that actually responds to that selection pressure.
How Common Is "Almost All of Them": Unpacking the Prevalence Data
Published prevalence figures for hemivertebrae in French Bulldogs range from 78 to 97 percent. A 2016 study of 105 French Bulldogs found an 85 percent prevalence rate. A separate imaging cohort found that 93.5 percent of neurologically normal Frenchies - dogs showing no symptoms at all - had at least one abnormal vertebra visible on x-ray.
That last figure is the one that surprises most buyers. The dogs in that cohort were not limping or wobbling. Their abnormalities were found only because researchers were looking.
This points to the most important practical fact about hemivertebrae: the published literature consistently finds that the vast majority of French Bulldogs with hemivertebrae never develop clinical neurological signs - estimates vary by study, but most suggest that 90 percent or more of affected dogs remain asymptomatic throughout their lives. A subset of affected dogs does show some neurological signs, and that range covers everything from a slight hind-limb wobble that stabilizes on its own to progressive paralysis requiring surgery. Most affected dogs who do show signs land toward the mild end of that spectrum.
The Three Types and the Mid-Thoracic Trouble Zone
Hemivertebrae are not all the same shape, and the shape matters for how the spine responds mechanically. There are three main morphological subtypes:
- Wedge vertebra: The vertebral body is taller on one side than the other. On a lateral x-ray it looks like a wedge instead of a rectangle. Depending on which side is compressed, this produces lateral curvature (scoliosis) or a forward arch (kyphosis). It is the most commonly identified type.
- Butterfly vertebra: The right and left halves of the vertebral body fail to fuse at the midline. On a dorsoventral x-ray - taken with the beam directed top-down - the result looks like a butterfly with wings spread. This type can be identified on plain radiograph without advanced imaging.
- Dorsal hemivertebra: Loss of tissue on the ventral side of the vertebra forces the spine into a kyphotic arch. Because the missing tissue is on the underside, the cord is compressed from below. This type tends to produce the most severe clinical signs and is the most likely to require surgical consideration.
The thoracic spine is the primary site of clinically significant hemivertebrae in French Bulldogs. Within the thoracic region, mid-thoracic vertebrae - commonly cited in the T8 through T11 range, though individual studies vary and no single vertebra has been definitively established as the universal most-common site - are most frequently implicated in cases that cause neurological signs. The rib cage limits how much the thoracic spine can compensate for an abnormal vertebral body, making malformations there more likely to narrow the spinal canal and compress the cord.
| Type | X-ray Appearance | Primary Spinal Effect | Surgery More Common? |
|---|---|---|---|
| Wedge vertebra | Asymmetric body, one side taller on lateral view | Scoliosis or kyphosis depending on orientation | Less often when stable |
| Butterfly vertebra | Butterfly shape on dorsoventral view | Variable; often mild if isolated | Rarely in isolation |
| Dorsal hemivertebra | Ventral deficiency, visible kyphotic arc | Direct cord compression from below | More likely with neurological signs |
Signs and Timeline in Puppies
What the 3-4 Month Window Looks Like
Clinical signs from hemivertebrae - when they appear at all - typically emerge between three and four months of age. This is when a puppy is growing rapidly and placing new mechanical demands on a spine that was already abnormally formed at birth.
Early signs can be subtle and easy to dismiss as normal puppy clumsiness:
- Hind-limb wobble or ataxia - the back end swaying while walking
- Bunny-hopping gait - using both hind legs simultaneously instead of alternating
- Reluctance to climb stairs or jump onto low surfaces
- Yelping or flinching when touched along the middle of the back
- Asymmetric muscle development in the hind limbs over time
- Loss of bladder or bowel control in more severe cases
The 9-Month Plateau
The piece of information almost entirely absent from consumer-facing content is this: neurological progression from hemivertebrae typically plateaus around nine months of age, when vertebral growth stops. A puppy that shows mild wobble at four months and does not worsen meaningfully by its first birthday carries a favorable prognosis for remaining neurologically stable throughout life.
How Hemivertebrae Raises IVDD Risk
French Bulldogs already carry elevated IVDD risk because of their chondrodystrophic status. When hemivertebrae are also present, that risk compounds through a specific mechanical pathway.
Hemivertebrae-induced kyphosis or scoliosis changes the angle at which compressive force passes through the discs adjacent to the malformed vertebra. Normal discs absorb load relatively evenly across their surface. An abnormally curved spine places asymmetric stress on neighboring discs - exactly the environment that accelerates degeneration in a breed already predisposed to disc disease. A French Bulldog with significant kyphosis in the mid-thoracic region and adjacent disc degeneration is dealing with both conditions at once, and the combination worsens prognosis compared to either condition alone.
Veterinary neurologists evaluating a Frenchie for hemivertebrae routinely assess disc health at adjacent levels as well. Treatment planning changes substantially when both problems are present at the same spinal location.
Diagnosis: What Each Imaging Modality Shows
Plain radiograph is the first-line tool. It confirms the presence, location, and basic morphology of hemivertebrae and gives a clear view of overall spinal curvature. For a buyer reviewing a breeder's health testing documentation, the spine x-ray is the image to look at.
When neurological signs are present and surgery is under consideration, MRI is the gold standard. MRI shows soft tissue detail that x-ray cannot - specifically, the degree of cord compression, whether signal change within the cord itself indicates injury, and the condition of discs at adjacent levels. CT provides three-dimensional detail useful for surgical planning but does not replace MRI's soft tissue resolution.
Questions worth asking a veterinary neurologist during an imaging consultation:
- Which vertebrae are affected, and what type is each malformation?
- Is there evidence of cord compression on MRI, and at which level?
- What is the condition of the discs immediately adjacent to the malformed vertebrae?
- Is the clinical neurological picture consistent with what the imaging shows?
- What would need to change clinically to move from monitoring to intervention?
Treatment: Conservative to Surgical
Conservative Management
Most affected dogs are never treated because they never show signs. For dogs with mild neurological signs, the standard first approach follows a clear sequence:
- Strict cage rest for four to six weeks, limiting movement to prevent further mechanical insult to an already compromised cord segment
- Anti-inflammatory medication - NSAIDs or a short course of corticosteroids - to reduce swelling around the affected area
- Canine physical rehabilitation, including underwater treadmill work and passive range-of-motion exercises, to maintain hind-limb muscle mass during restricted activity
- Neurological reassessment at the end of the rest period to determine whether improvement supports continued conservative care or whether a neurology referral for surgical evaluation is warranted
A published case series documented six French Bulldogs with acute paraparesis from hemivertebrae who showed improvement with acupuncture combined with Chinese herbal medicine after conservative medical management had not fully resolved their signs. This is a small series - not a controlled trial - but it appears in peer-reviewed literature and represents an option some veterinary rehabilitation specialists offer alongside conventional care.
Surgical Candidacy and Realistic Outcomes
Surgical spinal segmental stabilization, with or without cord decompression, is reserved for moderate-to-severe cases or those that fail conservative management. Published follow-up data from a case series of nine small screw-tail breed dogs - primarily Pugs and English Bulldogs, with findings considered applicable to French Bulldogs - covering two to six years post-surgery shows that four of nine operated dogs were neurologically normal at last follow-up, three had mild residual ataxia, one had moderate residual ambulatory weakness, and one relapsed at three and a half years. That is what the actual data says - not uniformly optimistic, not uniformly grim.
One practical consideration specific to French Bulldogs: general anesthesia in a brachycephalic patient carries baseline airway risk that does not apply to other breeds. At veterinary neurology referral centers, pre-surgical BOAS evaluation and dedicated airway planning are standard before any spinal procedure. If a surgeon does not raise airway evaluation during a surgical consultation for a Frenchie, ask about it directly.
What Responsible Breeders Actually Do
The FBDCA Protocol and Breeding Thresholds
The French Bulldog Club of America health testing protocol for breeding dogs includes a spine x-ray specifically to screen for hemivertebrae and other vertebral malformations. X-rays must be taken at or after twelve months of age to be submitted - a timing requirement that matters because vertebral development is not complete before that age, and earlier imaging can understate the final picture.
The threshold most commonly used by breeders who screen seriously is more than four hemivertebrae as a disqualifying criterion. That number requires context: a neurologically normal French Bulldog typically still has multiple abnormal vertebrae - the exact breed average varies by study, so discuss imaging results with a veterinary radiologist to understand how a given dog's count compares. A dog with four or fewer may be at or below the breed average in many studies. The goal of screening is harm reduction through gradual generational improvement, not eliminating a near-universal trait in a single breeding cycle.
Questions to Ask Before You Sign a Contract
Before committing to any French Bulldog breeder, ask these questions directly and expect specific answers:
- Has this dog - and both parents - had a spine x-ray submitted through the FBDCA health testing protocol?
- How many hemivertebrae were identified, and at which locations?
- Were any of the malformations in the thoracic region, specifically in the mid-thoracic area?
- What is the breeder's threshold for excluding a dog from breeding based on spine x-ray results?
- What does the health guarantee actually cover with respect to neurological conditions, and what does it require the buyer to do to make a claim?
A breeder who cannot answer these questions, or who dismisses spine x-rays as unnecessary because the dog looks fine, is not screening for this condition. That is not automatically bad faith - hemivertebrae is underrecognized in many breeding programs as well as among buyers. But it does mean the buyer is accepting risk they may not be fully aware of before signing.
Frequently Asked Questions
Can a French Bulldog with hemivertebrae live a normal life?
Yes, and many do. Published research consistently shows that the majority of affected dogs remain neurologically normal throughout their lives. Many more have mild early signs that stabilize before their first birthday and never progress further. The worst outcomes are typically seen in dogs with dorsal hemivertebrae causing direct cord compression or in dogs where hemivertebrae and IVDD are both present at the same spinal level.
If my puppy shows no symptoms, do I still need imaging?
Not as an emergency, but a baseline spine x-ray gives you information that matters if problems develop later. It tells you how many vertebrae are affected and where, which shapes what your vet looks for if neurological signs appear at two or three years of age. Some owners elect to do it at the first annual visit; others wait unless symptoms emerge. Discuss timing with your veterinarian based on what you know about the puppy's parents.
How is hemivertebrae different from a slipped disc in practical terms for an owner?
A slipped disc can happen acutely and often presents as sudden pain or paralysis in a dog that seemed fine the previous day - it is a disc failure event. Hemivertebrae cause compression through abnormal bone that has been there since birth, and when symptoms appear they usually develop gradually during the first months of life. The two conditions look different clinically, require different imaging priorities, and have different natural histories, which is why mixing up the two leads to misplaced expectations.
Will my general-practice vet find hemivertebrae on a routine visit?
Probably not, because routine wellness visits do not include spinal x-rays. A vet may note vertebral abnormalities if a thoracic x-ray is taken for another reason, but that is incidental. If you want your puppy's spine evaluated, request it specifically or ask for a referral to a veterinary neurologist for a formal spinal assessment.
What does "health tested" actually mean when a breeder says it?
In many French Bulldog breeding communities, "health tested" primarily means cardiac and eye evaluations. It does not automatically include spine x-rays, even though the FBDCA protocol offers a pathway for spinal screening. Always ask which tests were performed and whether spine imaging is included. A verbal assurance that the dog is healthy is not the same as documented spinal imaging reviewed against a known threshold.
Is hemivertebrae something the breed could eventually breed away from?
The heritability data suggests yes, over time and at scale. With heritability estimates above 0.5 for both the number of affected vertebrae and their severity, selection pressure through systematic x-ray screening can move breed-wide averages in a meaningful direction across generations. The challenge is that the same genetic mechanism producing the condition is tied to traits that have historically defined breed type. That is a long-term breeding community problem, not something a single buyer or breeder resolves - but understanding it explains why this condition is so persistent despite being so well documented.
