lumbosacral transitional vertebrae in the dog

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  • Lumbosacral Transitional Vertebrae in the Dog

    J. S. LARSEN

    INTRODUCTION

    At the junction of major divisions of the spine, a vertebra may take on characteristics of both divisions and be referred to as a transitional vertebra. Abnormal vertebral segments have been reported a t the cervi- cothoracic, thoracolumbar, lumbosacral, and the sa- crococcygeal junctions in the dog (1,2). The object of this paper is to report on the lumbosacral transitional segments observed as incidental findings in a large series of pelvic radiographs of purebred dogs and to discuss the clinical significance of this type of anomaly.

    MATERIALS AND METHODS

    Pelvic radiographs submitted to the Orthopedic Foundation for Animals (OFA) for review by the panel of cooperating veterinary radiologists are classified as to hip joint status with respect to canine hip dysplasia. Along with evaluation of hip joint status, incidental radiographic findings are noted and these findings are reported to the referring veterinarian and his client. Information from these reports is coded and stored in a computer for subsequent data retrieval. For this re- port, data was reviewed for all cases of transitional vertebrae observed since the computerization of the OFA program. Only breeds with one or more observed cases of transitional vertebrae were included for anal- ysis.

    RESULTS

    The 57 different breeds in which transitional verte- bral segments were observed at the lumbosacral area are listed in the Table. The 552 cases represent an inci- dence of 2.25% of the 24,463 evaluations under consid- eration. Chi-square analysis indicated that the German Shepherd Dog, Brittany Spaniel, Rhodesian Ridgeback, and Doberman Pinscher had significantly greater in- cidences of transitional segments than expected. No significant values were found when the variables of sex or hip joint classification were analyzed in relationship to the observation of transitional vertebral segments.

    Figure 1 is a tracing from a pelvic radiograph repre- senting the normal anatomical relationships of the lumbosacral junction. Figures 2-6 illustrate various types of transitional segments observed in standard ventrodorsal radiographs of the pelvic area.

    DISCUSSION

    Although in most instances the number of presacral vertebrae was not known, the author felt that the most common type of transitional vertebrae in the lumbo- sacral area was sacralization of the seventh lumbar vertebra. This was so when all lumbar segments could be counted. Lumbarization of the first sacral segment has been reported in the dog (1,2). This type of tran- sitional segment is not as obvious and can easily be overlooked, especially if the sacral area is partially ob- scured by rectal fecal contents or the preputial shadow. The spinous processes are the most useful landmarks in the anatomical identification of vertebral seg- ments.

    In man, sacralization of the fifth lumbar vertebra has been incriminated as a cause of severe low back pain, especially if the fusion is unilateral (4). In the dog, because of its quadrupedal stance, it is not likely that sacralization of the last lumbar vertebra will produce obvious clinical signs. When sacralization of the last lumbar vertebra is unilateral, a tilt in the pelvic axis is present in varying degrees. This tilt can result in compensatory spinal curvature, unequal placement of the hind feet in a resting stance, and gait irregularities such as crabbing which refers to moving with the body at an angle to the line of travel.

    Unilateral sacralization can make it nearlyimpossible to position perfectly an animal for hip dysplasia eval- uation. Cases of unilateral hip dysplasia caused by unilateral sacralization of the seventh lumbar vertebra have been reported (3). The asymmetric pelvis results in an increased slanting of the acetabular roof on the elevated side predisposing the joint to dysplastic change. Routine epidural injection is negated by lumbosacral anomalies because of distortion of the reference landmarks and fusion of the intervertebral space.

    One wonders what effect mans selection has on the

    From the Orthopedic Foundation for Animals, University of Missouri-Columbia, Columbia, MO 65201. Dr. Larsen is the OFA project director.

    76

  • VOL. XVIII LUMBOSACRAL TRANSITIONAL VERTEBRAE IN THE DOG 77

    TABLE Observations of Lumbosacral Transitional Vertebrae in Radiographs Submitted for Hip

    Dysplasia Evaluation

    No. of Observations

    No. of of Transitional Breed Evaluations Vertebra

    No. of Observations

    No. of of Transitional Breed Evaluations Vertebra

    Afghan Hound Akita Alaskan Malamute Anatolian Sheepdog Australian Shepherd Airedale Terrier Bloodhound Bernese Mountain Dog Bullmastiff Brittany Spaniel* Belgian Sheepdog Belgian Tervuren Boxer Borzoi Chesapeake Bay Retriever Chow Chow Collie Cocker Spaniel Cairn Terrier Doberman Pinscher* English Springer Spaniel French Briard Flat-Coated Retriever Great Dane Great Pyrenees Golden Retriever German Shepherd Dog* Giant Schnauzer Gordon Setter German Shorthaired Pointer

    897 304 952

    3 327 67 88 60

    111 643 93

    105 61 73

    255 84

    101 129

    5 487 344 35 32

    775 186

    2,613 2,596

    159 201 392

    21 7

    26 1

    10 2 3 1 4

    38 5 2 1 1 4 6 2 6 1

    18 1 1 1

    12 3

    20 111

    3 7

    11

    German Wirehaired Pointer Irish Setter Irish Wolfhound Keeshond Komondor Kerry Blue Terrier Kuvasz Lhasa Apso Labrador Retriever Mastiff Norwegian Elkhound Newfoundland Poodle Pudel Pointer Puli Rottweiler Rhodesian Ridgeback* Samoyed St. Bernard Standard Schnauzer Old English Sheepdog Siberian Husky Shetland Sheepdog Tibetan Terrier Vizsla Weimaraner Wirehaired Pointing Griffon

    126 1 1,467 38

    128 3 189 4 58 2 21 1 17 1 92 3

    2,735 49 63 4

    325 2 301 3 556 8

    2 1 97 2

    514 11 191 15

    1,061 21 478 3 155 3

    1,569 23 1,020 7

    229 6 28 1

    408 4 399 5 56 2

    TOTALS 57 24,463 522

    * Significant Chi-square value at 0.06 level one df.

    prevalence of transitional vertebral deformities. The four breeds with the highest incidence of deformity in this study all have peculiarities considered desirable by breeders. Brittany Spaniel breeders have selected for naturally tailless animals while Rhodesian Ridgebacks must have for show purposes the characteristic ridge of hair that grows forward along the top of the back. Both the Doberman stance with hind leg extension and the German Shepherd Dog show stance with one leg ex- tended and one leg set forward are intended to give the appearance of a level or sloping top line. Selection for these traits may be inadvertently increasing the prev- alence of transitional vertebral deformities.

    The prevalence of lumbosacral transitional vertebrae

    in purebred dogs is probably higher than the 2.25% in- cidence reported in this study in as much as many of the pelvic radiographs reviewed did not include all of the lumbosacral junction.

    SUMMARY

    Transitional vertebrae of the lumbosacral junction were observed as an incidental finding in 552 of 24,463 pelvic radiographs submitted for canine hip dysplasia evaluation (2.25%). The German Shepherd Dog, Brittany Spaniel, Rhodesian Ridgeback, and the Dob- erman Pinscher had the highest incidence of this

  • 78 J. S. LARSEN 1977

    Fig. 1. Tracing of the lumbosacral area from a ventrodorsal radiograph of a 33-month-old female Golden Retriever. The normal sacrum and vertebrae L6, L7, and C1 are illustrated.

    Fig. 3. Unilateral sacralization of L7 on the left side is seen.

    Tracing from a radiograph of a 31-month-old female Brittany Spaniel.

    Fig. 2. Tracing from a radiograph of a 31-month-old female Gordon Setter. The transverse processes of L7 are directed towards the ilia1 wings and form an abnormal syndesmosis.

    Fig. 4. Tracing from a radiograph of a 27-month-old female Afghan Hound. Sacratiration of LI is more pronounced. There was a compensatory spinal curvature in this dog.

  • VOL. XVIII LUMBOSACRAL TRANSITIONAL VERTEBRAE IN THE DOG 79

    Fig, 5. Tracing from a radiograph of a 41-month-old female Weimaraner. Bilateral sacralization of L7 with little asymmetry is seen. The ilia1 wings are flared.

    anomaly among the 57 breeds with one or more ob- served cases of lumbosacral transitional vertebra. Sacralization of the seventh lumbar vertebra appeared to be the most common form of this defect in the dog. The clinical significance of unilateral and bilateral transitional segments is discussed.

    Orthopedic Foundation for Animals University of Missouri-Columbia Columbia, MO 65201

    Fig. 6. Sacral fusion is complete. Flaring of ilia1 wings is present.

    Tracing from a radiograph of a 37-monthold female Labrador Retriever.

    ZUSAMMENFASSUNG

    Zwischenwirbel wurden zufaelling in der Kreuz-Lendenber- uehrungs-stelle in 552 von 24 463 Beckenroentgenaufnahmen (2,25%), die zur Beurteilung von Hueftendysplasie beim Hund unterbreitet worden waren, entdeckt. Der deutsche Schaeferhund, der Brittany Spaniel, der rbodesische Ridgeback und der Doberman Pinscher verzeichneten den groessten Anteil an dieser Abnormalitaet unter den 57 Rassen mit einem oder mehreren Faellen von Kreuz-Len- den-Zwischenwirbeln. Uebergang ins Kreuz des siebten Lenden- wirbels schien die haeufigste Form dieser Abnormalitaet beim Hund zu sein. Die klinische Bedeutung von einseitigen und zweiseitigen Zwischenteilen wird besprochen.

    RESUME REFERENCES

    1. Morgan, J. P.: Congenital Anomalies of the Vertebral Column of the Dog: A Study of the Incidence and Significance Based on a Radiographic and Morphologic Study. JAVRS 9: 21, 1968.

    2. Morgan, J. P.: Radiology of

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