Transitional Vertebrae in Dogs

Transitional vertebrae are congenital anomalies of vertebral segmentation that occur at the junction between two distinct regions of the spine. In dogs, the most commonly discussed form is the lumbosacral transitional vertebra (LTV), located at the junction between the seventh lumbar vertebra (L7) and the sacrum.

​The name alone makes it seem serious, but in reality, they are a relatively common congenital variation in the spine and in many cases, they don't lead to symptoms.
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Let’s break it down.

​What Is a Lumbosacral Transitional Vertebra?

​During embryologic development, vertebrae differentiate into cervical, thoracic, lumbar, sacral, and caudal segments. Transitional vertebrae arise when a vertebra at a regional boundary exhibits morphological characteristics of both adjacent regions.

​In the case of a lumbosacral transitional vertebra (LTV), the vertebra at the junction between the lumbar spine and the sacrum doesn’t form in a completely typical way.

Sometimes the last lumbar vertebra partially “acts like” a sacral vertebra, meaning it may be partially fused to the sacrum or shaped more like it. In other cases, the first sacral segment may resemble a lumbar vertebra, with incomplete fusion or differently shaped side projections (called transverse processes).

On radiographs, this can show up as:

• One side of the vertebra looking different from the other
• Enlarged or unusually shaped side projections
• Partial fusion where you wouldn’t normally expect it
• Subtle asymmetry of the sacrum
  
  

Importantly, this is something that develops before birth. It is not caused by exercise, sport training, jumping, trauma, or conditioning.

​How Common Are Transitional Vertebrae?

Transitional vertebrae are not rare, and their prevalence varies depending on breed and how dogs are screened.

Research has documented rates ranging from low single digits to well over 15% in certain working and sporting breeds. Differences in reported frequency often reflect variations in study design, classification criteria, and the populations being evaluated.

As spine radiographs have become more common in orthopedic screening programs, transitional vertebrae are being identified and documented more frequently than in previous decades. Increased detection, however, does not necessarily mean increased severity. In many cases, it simply reflects improved screening and greater awareness.

Do Transitional Vertebrae Cause Problems?

The lumbosacral junction is an important biomechanical transition point in the spine. It transfers force from the spinal column to the pelvis and hind limbs. Because of this, structural variations at this junction can potentially influence how forces are distributed through the lower back.

In some cases, transitional vertebrae may:

• Slightly alter load distribution
• Affect alignment of the sacrum and pelvis
• Change stress patterns on nearby discs or joints

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Certain forms, particularly those that are markedly asymmetric or structurally complex, have been associated in some studies with an increased risk of degenerative lumbosacral stenosis or cauda equina syndrome.

​However, many dogs with transitional vertebrae:

• Show no clinical signs
• Experience no pain
• Compete in demanding sports
• Work as service or working dogs
• Live full, comfortable lives

​The presence of a transitional vertebra on radiographs does not automatically mean a dog will develop back problems.

Severity and symmetry play a role. Mild, symmetrical transitional vertebrae are far less likely to carry clinical significance than pronounced asymmetry or more complex malformations. As with most orthopedic findings, radiographs must be interpreted alongside the individual dog’s clinical picture.

What Does It Mean on an OFA Report?

Transitional vertebrae are often identified during routine orthopedic screening, particularly when radiographs include the lumbosacral region.

The Orthopedic Foundation for Animals (OFA) will note transitional vertebrae as an incidental finding on both hip evaluations and formal spine evaluations. On OFA spine reports, the presence of a transitional vertebra is specifically indicated within the radiologist’s evaluation of the spinal segments.

​Importantly, OFA guidance states that transitional vertebrae are usually not associated with clinical signs and do not automatically disqualify a dog from being used in a breeding program. They recommend, when possible, breeding to dogs with a clear family history regarding transitional vertebrae.

In other words, it is a structural variation to be aware of, not an automatic disqualification.

Transitional Vertebrae and Hip Dysplasia

Some studies have explored correlations between LTV and hip dysplasia, hypothesizing that altered lumbosacral mechanics may influence pelvic orientation and acetabular loading.

While statistical associations have been documented in certain populations, LTV is not a causative diagnosis of hip dysplasia. Hip development is multifactorial and influenced by genetics, growth rate, environment, and overall conformation.

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Transitional vertebrae are one example of how radiographic findings require context and thoughtful interpretation. Structural variation does not automatically equate to dysfunction, and incidental findings should always be considered alongside the individual dog’s clinical picture.

As with most aspects of canine orthopedic health, informed evaluation and appropriate screening are key to making sound decisions.