Lumbosacral Transitional Vertebrae in Dogs: Classification, Prevalence, and Association With Sacroiliac Morphology

Abstract

The prevalence of lumbosacral transitional vertebrae (LTV) was determined by reviewing the pelvic radiographs of 4000 medium- and large-breed dogs of 144 breeds routinely screened for canine hip dysplasia. An LTV was seen in 138 (3.5%) dogs. The prevalence was higher in German Shepherd dogs and Greater Swiss Mountain dogs than in the other breeds, suggesting a genetic predisposition. There was no gender predisposition. The transverse processes of the LTV were divided into three types based on their morphological characteristics: lumbar type or type 1; intermediate type or type 2; and sacral type or type 3. In a symmetric LTV, both transverse processes are of the same type, while in an asymmetric LTV they are not. The frequency of occurrence of symmetric and asymmetric LTV was similar. In symmetric LTV, intermediate-type transverse processes predominated. Most of the asymmetric LTV had an intermediate-type transverse process combined with a lumbar or sacral type, respectively. Highly asymmetric LTV were often angled relative to the adjacent vertebrae. We hypothesize that an LTV is not the result of transformation of a lumbar into a sacral vertebra or vice versa, but rather is an autonomous intermediate type of vertebra. It occurs when the point of contact of the pelvis with the vertebral column is slightly cranial or caudal to its normal position. The resulting formative stimulus on the vertebral ossification centers, sagittally still separated, causes the various morphologies seen in LTV including the asymmetric variations.

Prevalence of lumbosacral transitional vertebrae in dogs in the Czech Republic

“…The LTV has the characteristics of both spinal segments, although definition varies in veterinary literature (Morgan 1968;Colter 1993;Morgan 1999;Damur-Djuric et al 2006;Westworth and Sturges 2010). It is assumed that the LTV is a predisposing factor for earlier degeneration of lumbosacral junction and it is a risk factor for development of cauda equina syndrome (Lang et al 1992;Morgan et al 1993;Flückiger et al 2006;Moore et al 2001).…”

“…Lumbosacral transitional vertebra (LTV) is a congenital abnormally formed vertebra between the last normal lumbar vertebra and the first normal sacral vertebra (Morgan 1968;Damur-Djuric et al 2006). The LTV has the characteristics of both spinal segments, although definition varies in veterinary literature (Morgan 1968;Colter 1993;Morgan 1999;Damur-Djuric et al 2006;Westworth and Sturges 2010).…”

“…It is assumed that the occurrence of LTV has a hereditary condition, although the type of inheritance of LTV has not been elucidated yet (Flückiger et al 2009). Prevalence of LTV in populations of dogs in different countries varies from 2.5 to 40.4% in dependence on the classification system (Morgan 1999;Damur-Djuric et al 2006;Ledecký et al 2007;Wigger 2009;Lappalainen et al 2012).…”

Fast running restricts evolutionary change of the vertebral column in mammals

“…3 K-N). Furthermore, in wolves, dogs, and humans, transitional lumbosacral vertebrae are associated with additional biomechanical problems in adjacent tissues, including increased pressure on blood vessels and nerves, intervertebral disk degeneration, iliolumbar ligament degeneration, scoliosis, and hip dysplasia (16)(17)(18). Hence, such transitional vertebrae are likely to dramatically reduce survival in species that depend on speed and agility to catch prey or to avoid predation.…”

“…Domestication and Inbreeding. Domesticated species usually harbor high numbers of transitional lumbosacral vertebrae, including those that originate from fast and agile wild counterparts (e.g., cats, dogs, and horses) (17,25,26) Human care relaxes selection by increasing the survival of less adapted individuals. Inbreeding probably also plays a role, as inbred wild wolves have higher numbers of transitional lumbosacral vertebrae than outbred ones (18,27).…”