Radiographic comparison of lumbar vertebral morphology between cats with six and seven lumbar vertebrae

The lumbar vertebral body length and height are common radiographic references used to assess abdominal organ size in dogs and cats; however, variation in vertebral count may influence the accuracy of these ratio-based assessments. This study compared the vertebral morphology in cats with six or seven lumbar vertebrae. Abdominal radiographs from 674 cats were reviewed and categorized into the six (6LV, n=102) and seven lumbar vertebrae groups (7LV, n=572). The vertebral body length, height, and height to length (H/L) ratio were measured from L1-L6 in all cats and at L7 in the 7LV group. Group comparisons were performed overall and by sex, and associations with sex, body weight, breed, and transitional vertebrae were analyzed. Additional adjusted analyses were performed to account for body weight and sex. Cats in the 6LV group had significantly longer vertebral bodies and lower H/L ratios at L1 to L5, whereas L6 was longer in the 7LV group. Vertebral body height was consistently lower across lumbar levels in the 6LV group. Vertebral length and height were positively correlated with body weight in both groups, and males had larger vertebrae than females. Overall transitional vertebrae prevalence did not differ between groups, but 13th rib hypoplasia was more common in the 6LV group. In adjusted analyses, lumbar vertebral count remained independently associated with vertebral body length, height, and H/L ratio. These findings demonstrate that lumbar vertebral count is associated with distinct morphological patterns that may affect vertebra-based organ size assessment in cats.