Hemivertebrae and other vertebral anomalies

Description: Several studies have shown that vertebral anomalies are common in brachycephalic dogs, such as Pugs (See references in Rohdin et al. 2018: 24). In a study by Rohdin et al. with the aim of investigating the clinical relevance of vertebral anomalies in Pugs, 57 Pugs were included, 30 of which had neurological symptoms and 27 were symptom-free. The Pugs had a median age of around 7 years. Of these Pugs, 96% had vertebral anomalies and each dog had an average of 3.6–3.7 defective vertebrae. The researchers found no clear correlation between vertebral defect and clinical relevance, but the vast majority of Pugs that had neurological symptoms (90%) had a defective vertebra just in connection with the defect of the spine from which the clinical symptoms originated. Since there were also Pugs that showed vertebral anomalies but no symptoms, Rohdin et al. write that one needs to investigate which other factors that contribute to the appearance of symptoms in relation to vertebral anomalies. At the same time, they did not rule out that the Pugs without symptoms could develop such when they got older (Rodin et al. 2018).

In Rohdin et al:s study, the following vertebral anomalies were found:

Hemivertebra, an average of 2.3 in those dogs who had this vertebral anomaly (29.6% without neurological symptoms, 23.3% with neurological symptoms)
Spina bifida which means that the vertebral body does not completely close to the spinal cord and then the latter can bulge and cause trouble (25.9% and 30.0% respectively)
Lack of the 13th thoracic vertebra that had developed into a transitional form between the thoracic and lumbar vertebrae (33.3% and 56.7%, respectively).

In another study of vertebral anomalies in Pugs, French Bulldogs and English Bulldogs by Ryan et al. (2017) 68 Pugs participated. It is not clear in the study how many Pugs in total that had any form of vertebral anomaly.

The following vertebral anomalies were discovered in the Pugs in Ryan et al:s study:

Six Pugs had one hemivertebra and six others had 2-3 hemivertebrae (17.6%)
Spina bifida, which means that the vertebral body does not completely close to the spinal cord and then the latter can bulge and cause trouble (38.2%)
Lack of the 13th thoracic vertebra that had evolved into a transitional form between the thoracic and lumbar vertebrae (30.9%)

4.7% of all Pugs that participated in Ryan et al:s study had clinically relevant vertebral anomalies, and in all cases they were hemivertebrae. Hemivertebrae are malformed vertebrae that can lead to the death of the Pug. The back gets an abnormal angle and can more or less “break off” and since this leads to lameness in the hind legs the Pug is often euthanized.

Although not all Pugs with hemivertebrae exhibited symptoms, one cannot rule out the possibility that such arose later in life, as the researchers point out. Similarly, the researchers emphasize that since T13 has become a transitional form between the thoracic and lumbar vertebrae of the Pugs as described above, the spine’s biomechanics is affected and it can cause secondary problems (Ryan et al. 2017: 28). Spina bifida can also cause problems in cases where the spinal cord bulges.

Although it is common in the Standard Pug with vertebral anomalies, it is not at all common, if it even occurs, in so-called altdeutsche Möpse or Old German Pugs (purebred sportier German Pugs), and the same applies to Retro Pugs. It seems that when the Pug gets a normal length of the back, these problems disappear.

Goal: No Pug should be born with hemivertebrae or other vertebral anomalies.

Below you see the Pug Bacchus who lives with a hemivertebra that has made him lame in the hind legs. On the right you see the X-ray image of his spine. Notice the 90 degrees angle of the spine.

Strategy: All dogs that are intended for breeding should be X-rayed or, if possible, CT-scanned. The dogs that have hemivertebrae should not be used in breeding. Pugs that have spina bifida should also be considered for removal from breeding. A Pug with a transitional vertebra should always be combined with a free one. In breeding we need to ensure that the Pug gets a normal length of the back and is not too compact. The Pug must be rectangular, not square in form. In this way, the vertebral anomalies will probably disappear by themselves.

Photo: Gitte Babbel
Mopszucht vom Minzenbach

Sources and further reading:

Rohdin, Cecilia et al. 2018. ”Presence of thoracic and lumbar vertebral malformations in pugs with and without neurological deficits”. The Veterinary Journal 241, 24–30.

Ryan, R. et al. 2017. “Prevalence of thoracic vertebral malformations in French bulldogs, Pugs and English bulldogs with and without associated neurological deficits”. The Veterinary Journal 221, 25–29.

Chapters in Strategies for the breeding of Healthy Pugs