Articular Process Malformations in Brachycephalic Breeds

Caudal articular process dysplasia has been identified in several breeds, including French bulldogs, English bulldogs, and pugs; however, this condition does not always result in clinical disease. A group of veterinary neurologists and surgeons in London and Utrecht studied the prevalence and clinical relevance of this malformation.

Study Design

In this retrospective study, medical records from the Royal Veterinary College at the University of London from October 2010 to November 2016 were searched for French bulldogs, English bulldogs, and pugs that had undergone computed tomography (CT) of the complete thoracic vertebral column for reasons unrelated to neurologic or orthopedic disease, and had complete medical records available for review. Cases were excluded from analysis if neurologic or orthopedic disease was reported, if medical records were incomplete, or if CT studies were incomplete.

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The occurrence, location, and number of hypoplastic or aplastic caudal articular facets were recorded for each dog and compared between breeds. Dogs were assigned to either an “unaffected” or “dysplasia” group for analysis. The dysplastic group was further classified into focal (only 1 region of affected vertebrae, with <7 total vertebrae affected), multifocal (multiple regions of affected vertebrae, with <7 total vertebrae affected), or generalized (>7 vertebrae affected). Data were evaluated for normality, and statistical analyses were corrected for repeated measures and multiple comparisons. Breed-specific prevalence of articular process hypoplasia and aplasia were calculated for each site, with age and sex as covariates.

Results and Discussion

Included in the study were 271 dogs that met inclusion criteria (108 French bulldogs, 63 English bulldogs, and 100 pugs). Of these 271 dogs, 226 (83.4%) had caudal articular process hypoplasia or aplasia in the thoracic vertebrae. Among the dogs, 3506 vertebrae were evaluated, of which 1104 (31.5%) were affected. Hypoplasia was identified in 198 of 271 dogs (73.1%) and 476 of 3506 (13.6%) vertebrae. One-hundred eighty four of 271 dogs (67.9%) and 628 of 3506 vertebrae (17.9%) had aplasia.

By breed, 76 of 108 French bulldogs (70.4%) had dysplasia. Twenty-nine of these (26.9%) were hypoplasia, and 47 (43.5%) were aplasia. Dysplastic facets were classified as focal in 27 (35.5%) of the 76 affected French bulldogs, multifocal in 45 (59.2%), and generalized in 4 (5.3%). The most commonly affected vertebrae were T10 followed by T11.

Fifty-three of the 63 English bulldogs (84.1%) had dysplasia, with 12 of 63 (19%) showing hypoplasia and 41 of 63 (65.1%) showing aplasia. Dysplastic facets were classified as focal in 22 of the 53 affected English bulldogs (41.5%), multifocal in 23 (43.4%), and generalized in 8 (15%). Aplasia most commonly affected T4 followed by T9, whereas hypoplasia most commonly affected T10 followed by T11.

Of the 100 pugs evaluated, 97 (96%) showed dysplasia. One of these (1%) was hypoplasia, and 96 (96%) were aplasia. The pattern was focal in 9 of these dogs (9.3%), multifocal in 33 (34%), and generalized in 55 (56.7%). In pugs, T10, T3, T11, and T12 were the most commonly affected sites for aplasia, in that order, with hypoplasia most commonly affecting T4 and T9.

Age and sex were not significantly associated with prevalence, but breed was.

Clinical Impact

Caudal articular process hypoplasia and aplasia are very prevalent in nonclinical pugs (96%), English bulldogs (84.1%), and French bulldogs (70.4%), with multifocal (French and English bulldogs) and generalized (pugs) occurrences being encountered most commonly. Although clinical signs can occur in dogs with caudal articular process aplasia, the majority of dogs with these malformations do not develop clinical signs.

Dr. Packer is an associate professor of neurology/neurosurgery at Colorado State University College of Veterinary Medicine and Biomedical Sciences in Fort Collins and is board certified in neurology by the American College of Veterinary Internal Medicine. She is active in clinical and didactic training of veterinary students and residents and has developed a comparative neuro-oncology research program at Colorado State University.