TRANSITIONAL VERTEBRAL SEGMENT (TVS)
There has been a flurry of questions in recent years about conditions known as TVS and APA (asymmetrical pelvic attachment), which makes me wonder it is the incidence or the diagnosis that is on the rise. A malformation of vertebrae, usually the last lumbar or first sacral vertebra (sometimes more than one per case) is simply and aptly called “Transitional Vertebrae”. This congenital and inherited defect begins in that stage of embryo development when differentiation is nearly complete, but a vertebral body “can not make up its mind whether it wants to be part of the lower lumbar vertebral column or part of the sacrum”, as colorfully described by OFA’s Dr. Greg Keller, and it winds up taking on bony characteristics of both lumbar vertebrae and sacrum. Less common are the transitional vertebrae seen at the thoracic-lumbar junctions.
Veterinary-science observer Barbara Nibling describes mild cases this way: “The processes are just a bit odd, one set of processes looking as if the T13 belongs to the lumbar group, while the other side looks like a normal T13.” Many go unnoticed unless there is a rib on one side but not on the other, in which case the difference leaps out at you. 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. If it results in less symmetry there, the condition is usually referred to as APA.
The transitional vertebral body takes on some of the characteristics of both, and is an abnormality that may have a causative role in the severity or nature of HD, although by itself it seems not to have any bad effects. It is developmental, and its inherited nature is extremely probable, having been identified as familial and being similar in many ways to other known genetic defects. Frequency of transitional vertebrae runs from quite low (zero in Saints, 3% in Labs) to somewhat higher (8-11% in German Shepherd Dogs), and most cases (69%) are associated with HD. That is, most but not all cases are found in dysplastic dogs. This is one reason why the frequency of asymmetrical HD is as high as it is (30% in the GSD, for example — more than in other breeds).
The trait is probably polygenic; at least it cannot be said to be simple. It is definitely familial; for example, Borzoi breeder Bonnie Dalzell reports around 40% of the dogs that were radiographed in a program she participated in had lumbo-sacral transitional vertebrae! She described them as “much slower gallopers at field trials than the dogs with normal anatomy” or having reduced interest in running at a fast gallop. Top racers, she said, can go 33 mph, while dogs with “weird backs” generally top out at 23 to 24 mph. She also surmised that many cases might be missed, if the transitional vertebrae were further toward the front of the dog, because of the great size of her breed — the crest of the ilium of the pelvis and the last lumbar vertebrae might not be included in the standard 17-inch film, and thus any TVS not observed. Field trial performance, for which she is well known and highly respected, is affected, so she naturally pays more attention to searching for the anomaly than most people might. She has had eager coursing dogs with TVS, and found them not as fast as the ones without it. Her meticulous observation has uncovered other little-known “symmetry anomalies” such as one in which there is an extra lumbar vertebra. This would be highly unusual in dogs, although there is a breed of pigs with an extra pair of ribs, and differences in number of cervical vertebrae between animals such as giraffes and squirrels (the numbers may surprise you!). Dogs with the extra vertebrae in the loin and other lumbo-sacral anomalies seem to be prone to having symptoms of something that vaguely resembles “Wobblers”, also displayed neurological deficiencies in the hind legs, and were relatively poor gallopers, according to Dalzell. Another fairly location of transitional vertebrae is in the thoraco-lumbar region, in which, she says, “the dog may have one less rib on one side than the other. This does not seem to affect performance at a gallop.”
The abnormal attachment of these segments causes the pelvis to be rotated a little in a longitudinal fashion, which means the pelvis is tilted so one femoral head gets more coverage by the acetabulum than the other side does, and as we see in Chapter 8 of the second edition of my HD/Orthopedic Disorders book, this tends to draw laxity or joint ligament weakness into subluxation. Yet it is not so much the fact that transitional vertebrae are there, as what effect they have on pelvic attachment that is important. TVS does not participate in causing HD unless it does so through intermediately causing APA. Asymmetry in pelvic attachment is highest in Labs and GSDs (around 7-8%) and 79% of these cases are associated with HD. While transitional vertebrae and asymmetrical pelvic attachment may not cause all cases of unilateral HD, they do appear to uncover it or make bilateral laxity look like unilateral HD, at least on the hip-extended view. An important conclusion of this ten-year study is that the quality of hip joints is not independent of the nature of pelvic vertebral attachment.
More acronyms are not what I enjoy, but these abbreviations are helpful. In orthopedic lingo, the condition of asymmetrical (without symmetry) pelvic attachment of the last vertebrae before the sacrum, is called APA. The condition of transitional vertebral segments is referred to as TVS. The fact that TVS and APA are associated with unilateral HD or differences in the severity of one side vs. the other, is why the OFA looks for these signs and requires a full picture of the pelvis be included on each hip radiograph submitted for evaluation/certification. The incidences of both APA and TVS in “normal” dogs are quite low, but these conditions do exist independently of HD in a small number of dogs with otherwise normal hips. For example, APA was 2.8% and TVS 1.4% in Labrador Retrievers with normal hip joints, but 13.8% and 5.2%, respectively, in dysplastic Labs. There are similar or perhaps identical conditions in humans.
The L7 to S1 region of the spinal column is where some see what they call “block vertebra”, referring to a somewhat unusual shape. Not only are affected coursing sighthounds slower, according to some in the sport, but most dogs upon very careful motion analysis will evidence an asymmetric gait. The last lumbar vertebra can be fused on one side to either the first sacral vertebra, or its process (“wing”) can bridge over to near the top of the ilium. In any case, the dog has more articulation, and range of movement and flexion/extension on one side than the other. Many have noticeably shorter stride, but this can also be the result of other problems, such as arthroses in any of the four limbs’ joints. In people, this is an indicator of future problems in the lower back due to points of stress in humans.
Is TVS a serious problem? Many think not, but I believe their lack of concern is based on old information that indicated TVS was not a significant problem. In a conversation between the OFA and GSD fancier Rita Ledda (via e-mail chat list) about transitional vertebrae, she was told that it is not a big problem; yet OFA recommends an affected dog not be bred to a mate that also has transitional vertebrae. They say that normally, TVS or APA by itself (without concurrent HD or another disorder) does not affect the dog. There might be some concern about dogs that engage in some type of pulling competition, a big sport in Malamutes, American Bulldogs, and American Pit Bull Terriers. The stress may cause irritation at the sacrum joint. It must be kept in mind that there could be a relationship between TVS and other disorders, too. Morgan et al found that in German Shepherd Dogs, at least, the presence of lumbosacral transitional vertebrae is a predisposing cause of cauda equina syndrome; this disorder is treated in another article.
Another GSD fancier, trainer, and writer named Ricardo Carbajal reported (on an e-mail list) a December 1996 conversation with Dr. Keller of OFA in which Keller said that TVS is a developmental problem. When the puppy is developing in utero, some of the lumbar vertebrae attach firmly or tenuously to the sacrum. You usually see bony changes that are more similar to the sacral area; one of those changes is that the transverse process (the side wing) deforms or “bends” and fully or partially fuses to the ilium. Some times you also see that the inter-vertebral space is diminished or absent. Usually this problem does not affect the health of the individual. But it does tend to run in families, so it should be considered a genetic defect and given whatever amount of serious attention you decide it deserves.
Morgan has done much work in this area, and says that transitional vertebrae “can occur at the site of junction of the major portions of the vertebral column, i.e., occipito-atlanto-axial, cervico-thoracic, thoraco-lumbar, and lumbosacral. The spinal segments at these sites are altered so they have features in common with those either cranial or caudal” [to them]. When we speak of transitional vertebrae, we should also describe the specific nature of the change, such as where the attachment is directed, and whether it is unilateral or bilateral. Some TV are symmetrical, equal on both sides. Others are asymmetrical (APA); “for example, a lumbar transverse process on one side and a heavy wing on the other that attaches to the sacrum.” Transitional lumbo-sacral vertebra (TLSV) was found in 38% of German Shepherd Dogs diagnosed with cauda equina syndrome. Is there a biochemical/genetic connection, or are such dogs selected for by sloppy breeding practices in general?
For a long time, it was generally thought that these abnormal vertebral segments and attachments did not cause pain and therefore had little clinical or breeding significance throughout a dog’s lifetime. Currently, the feeling is that such lesions at the lumbosacral junction predispose the dog to further weakness, instability, excessive motion around that disc, creation of cauda equina syndrome, and possibly a worsening of hip joint laxity or instability. TVS can weaken an already unstable sacro-iliac joint and put additional stress on the joint between the sacrum and the last lumbar vertebra.
NOTE: A well-respected AKC
and Schaferhund Verein
judge, Mr. Lanting has judged in more than a dozen
countries, including the prestigious FCI Asian Show hosted by Japan Kennel
Club, the Scottish Kennel Club, a Greyhound specialty in