Genetic Welfare Problems of Companion Animals

An information resource for prospective pet owners

French BulldogFrench Bulldog

Hemivertebrae

Related terms: Congenital vertebral anomalies, wedge vertebrae

Outline: French bulldogs commonly have deformities of the bones of the spine. These can lead to pressure on the spinal cord resulting in progressive pain and loss of hind limb function and incontinence.


Summary of Information

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1. Brief description

Hemivertebrae are bones of the spine that are abnormally shaped. Because of their abnormal shape these bones tend not to align correctly with their neighbouring bones in the spine. This can lead to instability and deformity of the spinal column, which in turn can lead to the spinal cord or the nerves arising from it becoming squashed and damaged. This causes pain – which can be severe - wobbliness (ataxia) on the hind legs and can also cause loss of hind leg function and incontinence (inability to control passing urine or faeces). It appears that the disease is a consequence of selecting for the screw (curly) tail conformation of this breed. The screw-tail shape is due to abnormal shape of tail bones but this abnormality can also affect other parts of the spine with serious consequences as outlined above.

2. Intensity of welfare impact

Pain from spinal cord compression (squashing) can be severe. Affected dogs can also lose function in their hind limbs and sometimes lose bladder and bowel control. Not all animals with hemivertebrae develop these signs; some have milder signs of ataxia or no signs at all.

Dogs with severe signs may need major surgical interventions, which have their own welfare impacts, and, despite this, some may not recover and need to be euthanized on humane grounds.

3. Duration of welfare impact

Young dogs are most commonly affected when problems associated with skeletal deformities develop as their skeleton grows. The skeletal deformity is permanent without surgery. The clinical signs associated with the condition can develop rapidly over days, or gradually over weeks and months. Severely affected individuals would, without surgery, have permanent major disability. Even where surgery is possible, some animals may have unacceptable levels of disability necessitating euthanasia.

Thus this condition can severely limit both the quality and length of life.

4. Number of animals affected

The exact numbers affected are not known, but it is considered a common problem in French bulldogs and other brachycephalic (short-nosed) breeds that have screw-tails. Selection for screw tails, which are caused by deformed vertebrae, has the unintended consequence of causing deformity higher up the spine also. Screw tail describes a tail which, in its relaxed position, is coiled, usually to one side. The most severely affected tails cannot be straightened at all, others can be manually straightened but relax back into the coiled position.

5. Diagnosis

A diagnosis is made on examination and radiography (taking x-ray pictures).

6. Genetics

The exact genetics of this condition have yet to be worked out; however, French bulldogs are considered to be predisposed to hemivertebrae because of the breed characteristic of a screw-tail. The gene(s) causing the screw-tail deformity (which involves hemivertebrae in the tail) are thought also to be involved in producing hemivertebrae elsewhere in the spine.

7. How do you know if an animal is a carrier or likely to become affected?

All French bulldogs are prone to the problem because the breed has a screw-tail. That a dog has no hemivertebrae can only be confirmed by taking x-rays of the spine.

8. Methods and prospects for elimination of the problem

Not known, though whilst the breed standard includes a screw-tail the condition seems likely to persist. It seems likely, since the screw tail is caused by hemivertebrae in the tail, that out-breeding to dogs with straight tails, then selection for a straight tail might be a way forward to eliminate this welfare problem.

 

For further details about this condition, please click on the following:
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1. Clinical and pathological effects

An understanding of the anatomy of the normal spine of the dog is useful in understanding this condition.

Hemivertebrae figure 1

Figure 1. The regions of the spine.

The spine or spinal column of dogs is made up of many bones, called vertebrae and it is divided into 5 different regions. There are 7 bones in the neck (cervical) region, 13 in the chest (thoracic) region, 7 in the lower back (lumbar) region and 3 fused together to form the sacrum (at the hips). Lastly, there are the tail (coccygeal) bones, and their number varies. In French bulldogs and other screw-tailed dogs there are relatively few coccygeal vertebrae. Vertebrae are numbered according to region of the spine, starting from the head and working towards the tail. Thus the first cervical vertebra is called C1, the second C2 and the first thoracic vertebra is T1 etc. Intervertebral discs are found between the vertebral bodies.

The body of each vertebra is positioned ventrally (towards the lower side). Dorsal (towards the back of the dog) to the vertebral body each vertebra forms a hollow tube of bone, called the vertebral canal. Through this tube created by the column of vertebral canals the spinal cord passes, connecting the base of the brain with peripheral nerves. This tube of bone protects the spinal cord. The spinal cord is made up of delicate nerve tissue which transmits the messages between the brain and other parts of the body (excluding the head). 

Hemivertebrae figure 2

Figure 2. Diagram showing the shape of normally-formed vertebrae in the spinal column and how the spinal cord runs through them.

Each vertebral body develops in the foetus from two separate parts which fuse together and then ossify (turn to bone). Hemivertebrae occur when this fusing process fails to happen correctly so that the vertebral body of one or more vertebra is malformed and wedge-shaped (LeCouteur and Child 1995). Often the fusion or ossification is asymmetrical (Jeffery et al 2007). The malformations vary, with the apex of the wedge pointing dorsally, ventrally or medially (towards the middle of the animal) across the midline (LeCouteur and Child 1995). These abnormally-shaped vertebrae often lead to alterations and deformities in the shape of the spine such as kyphosis (curving upwards of the central spine), scoliosis (deviation to the side in the central spine) or lordosis (curving downwards in the central spine) (LeCouteur and Child 1995). This angulation of the spine is often moderate to severe and can lead to displacement of the vertebrae (LeCouteur and Grandy 2000). The deformity or instability in the spinal column can then narrow the vertebral canal, compressing and damaging the spinal cord, and this can lead to serious clinical signs (LeCouteur and Child 1995). This spinal deformity and the consequential clinical signs often progresses as the dog grows or, sometimes, happen secondary to mild trauma because of the spinal column instability (LeCouteur and Grandy 2000).

Hemivertebrae figure 3

Figure 3. Abnormal development of vertebral bodies results in formation of hemivertebrae.  

Unlike the normal shape of vertebrae shown in Figure 2, in which the opposing faces of adjacent vertebrae are at right angles to the line of the spine, wedge shaped vertebrae as shown here can lead to distortion of the spine with health and welfare effects.

Hemivertebrae figure 4

Figure 4. Radiograph of a hemivertebra in the thoracic region of a Pug. The wedge shaped vertebra has caused lordosis of the spine, which in turn can cause compression and damage to the spinal cord. (Image property of Helen McDonald, to whom we are grateful for permission to reproduce it here).

Hemivertebrae can occur in any breed but are most common in brachycephalic, screw-tailed dogs such as French bulldogs (also English bulldogs, Pugs and Boston terriers). This is because the kinked tails that many find desirable in these breeds result from hemivertebrae in the tail region of the spine and these breeds have genes that tend to cause the formation of hemivertebrae elsewhere in the spinal column as well as in the tail (LeCouteur and Grandy 2000). The commonest region of the spine to be affected by hemivertebrae, in French bulldogs, is the chest (the thoracic area (LeCouteur and Child 1995).

Hemivertebrae figure 5

Figure 5. Hemivertebrae is the cause of kinked or screw tails in some breeds of dog, such as the Boston Terrier and Pug (shown here). This condition makes them prone to developing hemivertebrae elsewhere in the spinal column also. (Image sourced from Wikipedia at www.wikipedia.org/Pug).

Hemivertebral abnormalities commonly occur without clinical sign of disease (Done et al 1975). However, if the spinal cord becomes damaged or compressed signs appear. Signs include posterior paresis (abnormal functioning of the hindlimbs), muscle wastage, an abnormal shape to the back and back pain. If the problem is severe then the dogs can lose all use of their hind legs and can have urinary and faecal incontinence (inability to control passing urine or faeces). Signs can be gradual or rapid in onset and sometimes are progressive (Colter 1993). In a number of cases, however, signs may be mild and non-progressive and stabilise once the dog has stopped growing at about 9 months of age (Jeffery et al 2007), though the deformity will remain. In these cases no treatment may be necessary. (Skin infections and other skin problems can occur in skin folds if the tail is very tightly coiled).

In severely affected individuals the only hope is major surgery of the spine to attempt stabilisation and to stop the spinal cord being compressed. This is not straightforward, needs specialist veterinary treatment and may not always be successful. Some dogs which are completely paralysed in their hind legs may not recover use of them after surgery.

Paralysed dogs have long-term care needs which many owners find difficult and some dogs will be euthanized because of this. It is an ethical dilemma whether these permanently paralysed dogs should be euthanized or if their quality of life may be sufficient to justify supported living with paralysis and incontinence.

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2. Intensity of welfare impact

Some dogs with hemivertebrae suffer no apparent ill effects however others have major welfare problems such as pain, loss of function of the hindlimbs and incontinence. Pain from spinal cord compression can be significant and severe and difficult to control using drugs.

Along with pain, the spinal cord damage in severely affected individuals leads to the need for rapid veterinary treatments including major surgery. Though some dogs recover, surgical treatment is a major intervention and many animals have a prolonged recovery during which veterinary staff and owners need to carry out extensive treatment and nursing which interfere with the dog’s life and daily routine. Some animals may not recover and may need to be euthanized.

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3. Duration of welfare impact

The condition usually first manifests in young growing dogs and worsens as growth proceeds. In a case study by Jeffery et al (2007), all three dogs described were less than 7 months of age. Though some may be mildly affected, all affected animals will have permanent deformity unless surgical intervention is used. The disease problems can develop rapidly over hours or more gradually. Though some dogs with hemivertebrae do not develop signs, others develop severe problems which will not improve unless surgical intervention occurs. Some dogs with severe signs may not improve after surgery and may need to be euthanized.

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4. Number of animals affected

The numbers affected are not known, but it is considered a common problem in French bulldogs and other brachycephalic (short-nosed) breeds that have screw-tails, as the deformity is connected to the screw-tail phenotype (physical shape) which is a breed characteristic.

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5. Diagnosis

The condition may be suspected in any French bulldog with spinal deformity or with the characteristic clinical signs because it is commonly seen within the breed. A diagnosis can be made using plain and contrast radiography (x-rays, with or without dye, which shows up on the x-ray being injected around the spinal cord), however, Jeffery et al (2007) believe MRI (magnetic resonance imaging) scans are needed prior to surgery to help decide on exact surgical requirements.

The presence of hemivertebrae seen on x-rays may also be a confusing finding. Older French bulldogs may have spinal disease from other causes and detection of hemivertebrae may make diagnosis of the real cause difficult.

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6. Genetics

The exact genetics of this condition have yet to be worked out; however, French bulldogs are considered to be predisposed to hemivertebrae because of the breed having a screw-tail (Jeffery et al 2007). The, as yet unknown, gene/s that cause the screw-tail deformity (which involves hemivertebrae in the tail), are thought to also produce hemivertebrae elsewhere in the spine.

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7. How do you know if an animal is a carrier or likely to become affected?

All French bulldogs are potentially prone to the problem because the breed has a screw-tail. Without x-ray images of the spine, definite absence of hemivertebrae cannot be confirmed. However, a mature animal without signs has a lower chance of developing clinical problems than a puppy which has yet to undergo its period of significant growth.

Currently no advice can be given on how to ensure a healthy individual, free from the condition, is not a carrier. This may become clearer when the genetics of the condition are better understood.

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8. Methods and prospects for elimination of the problem

Not known, though whilst the breed standard includes a screw-tail the condition seems likely to persist. It seems likely, since the screw tail is caused by hemivertebrae in the tail, that out-breeding to dogs with straight tails, then selection for a straight tail might be a way forward to eliminate this welfare problem.

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9. Acknowledgements

UFAW is grateful to Rosie Godfrey BVetMed MRCVS and David Godfrey BVetMed FRCVS for their work in compiling this section and to Hazel Bentall BVSc MRCVS for her comments on it.

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10. References

Colter S (1993) Congenital anomalies of the spine. In Bojrab M (Ed) Disease mechanism in Small Animal Surgery. 2nd Ed. London: Lippincott, Williams and Wilkins

Done S, Drew R and Robins G (1975) Hemivertebra in the dog: clinical and pathological observations. Veterinary Record 96: 313

Jeffery N, Smith P and Talbot C (2007) Imaging findings and surgical treatment of hemivertebrae in three dogs. Journal of the American Veterinary Medical Association 230: 532-536

LeCouteur R and Child G (1995) Diseases of the spinal cord. In Ettinger S and Feldman E (Eds) Textbook of veterinary internal medicine. 4th Ed. Philadelphia: WB Saunders Company

LeCouteur R and Grandy J (2000) Diseases of the spinal cord. In Ettinger S and Feldman E (Eds) Textbook of veterinary internal medicine. 5th Ed. Philadelphia: WB Saunders Company

© UFAW 2011


Credit for main photo above:

http://depositphotos.com/11051798/stock-photo-french-bulldog-standing-on-the.html

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