Transitional Vertebral Segments, TVS

Vertebral body anomalies are readily recognized by veterinarians, as it is possible to use hip-radiographs to diagnose transitional vertebral segments in dogs. Transitional segments have characteristics of one portion of the vertebral column, yet when the vertebrae are counted, they belong in another segment. This congenital and inherited defect begins in that stage of embryo development when differentiation is nearly complete, but a vertebral body develops in such a way that it is a part of the lower lumbar vertebral column and part of the sacrum at the same time, and has bony characteristics of both lumbar vertebrae and sacrum. Many go unnoticed unless there is a rib on one side but not on the other. The affected part is called TVS, Transitional Vertebral Segment. It apparently can happen anywhere along the spinal column, but in the lumbo-sacral area most often.

Most cases of TVS are associated with hip dysplasia. That is, most but not all cases are found in dysplastic dogs. Some breeders report that their affected dogs show less interest in running and may be not as fast as unaffected dogs.

TVS and Cauda Equina Syndrome

Transitional vertebral anomalies have for some time been suggested as a possible cause of cauda equina syndrome, disease or injury involving multiple spinal nerve roots, especially in the German shepherd dog (a condition recently thought to be inherited). Other working breeds are also affected. This condition is characterised by separation of the first sacral segment and spinous processes between what are normally the first and second sacral segments. The effect of the weakening of the sacroiliac attachment was thought to result in premature disc degeneration, which, together with spinal canal stenosis, results in potential compression of the overlying spinal nerves and creation of a cauda equina syndrome.

Dogs at Risk

The condition is thought to have clinical significance and should be selected against in breeding, especially in the German Shepherd dogs. The condition is usually found more frequently in the female than in the male.

References:
1. Transitional lumbosacral vertebral anomaly in the dog: a radiographic study. Morgan JP. In: J Small Anim Pract. 1999 Apr;40(4):167-72.
2. TVS, Caudal Equina Syndrome, and Spondylosis. Fred Lanting.