Developmental variation in lumbosacropelvic anatomy of Thoroughbred racehorses

Kevin K. Haussler From the Department of Anatomy, Physiology and Cell Biology (Haussler, Stover), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616.

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Susan M. Stover From the Department of Anatomy, Physiology and Cell Biology (Haussler, Stover), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616.

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Neil H. Willits From the Department of Anatomy, Physiology and Cell Biology (Haussler, Stover), School of Veterinary Medicine, and the Statistical Laboratory (Willits), University of California, Davis, CA 95616.

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Abstract

Objective

To describe the incidence and types of gross osseous developmental variations and ages of physeal closure in the caudal portion of the thoracic and lumbosacral spine and the pelvis in a sample of Thoroughbred racehorses.

Animals

Thoroughbred racehorses (n = 36) that died or were euthanatized at California racetracks between October 1993 and July 1994.

Procedure

Lumbosacropelvic specimens were collected, and all soft tissues were removed. The osseous specimens were visually examined.

Results

Only 22 (61 %) specimens had the expected number of 6 lumbar and 5 sacral vertebrae. Eight (22%) specimens had thoracolumbar transitional vertebrae, and 13 (36%) had sacrocaudal transitional vertebrae. Articular process asymmetries were present at 1 or more vertebral segments in 30 (83%) specimens. Intertransverse joints (2 to 4 pairs/specimen) were bilaterally distributed in the caudal portion of the lumbar spine and the lumbosacral joint in 31 (86%) specimens. Five (14%) specimens had asymmetric distribution of the intertransverse joints. Intertransverse joint ankylosis was found in 10 (28%) specimens. Lumbosacral vertebral body physeal closure occurred between 4.9 and 6.7 years of age; pelvic physeal closure occurred between 5.2 and 5.8 years of age. Iliac crest and ischial arch epiphyseal formation was evaluated, using a grading system, and fusion to the underlying bone occurred at 7.2 years and 5.4 years of age, respectively.

Conclusions

Numerous vertebral anatomic variations were commonly found in a sample of Thoroughbred racehorses.

Clinical Relevance

Normal anatomic variations and ages of skeletal maturity need to be considered in clinical evaluation of the equine spine and pelvis for differentiation from pathologic findings. (Am J Vet Res 1997;58:1083–1091)

Abstract

Objective

To describe the incidence and types of gross osseous developmental variations and ages of physeal closure in the caudal portion of the thoracic and lumbosacral spine and the pelvis in a sample of Thoroughbred racehorses.

Animals

Thoroughbred racehorses (n = 36) that died or were euthanatized at California racetracks between October 1993 and July 1994.

Procedure

Lumbosacropelvic specimens were collected, and all soft tissues were removed. The osseous specimens were visually examined.

Results

Only 22 (61 %) specimens had the expected number of 6 lumbar and 5 sacral vertebrae. Eight (22%) specimens had thoracolumbar transitional vertebrae, and 13 (36%) had sacrocaudal transitional vertebrae. Articular process asymmetries were present at 1 or more vertebral segments in 30 (83%) specimens. Intertransverse joints (2 to 4 pairs/specimen) were bilaterally distributed in the caudal portion of the lumbar spine and the lumbosacral joint in 31 (86%) specimens. Five (14%) specimens had asymmetric distribution of the intertransverse joints. Intertransverse joint ankylosis was found in 10 (28%) specimens. Lumbosacral vertebral body physeal closure occurred between 4.9 and 6.7 years of age; pelvic physeal closure occurred between 5.2 and 5.8 years of age. Iliac crest and ischial arch epiphyseal formation was evaluated, using a grading system, and fusion to the underlying bone occurred at 7.2 years and 5.4 years of age, respectively.

Conclusions

Numerous vertebral anatomic variations were commonly found in a sample of Thoroughbred racehorses.

Clinical Relevance

Normal anatomic variations and ages of skeletal maturity need to be considered in clinical evaluation of the equine spine and pelvis for differentiation from pathologic findings. (Am J Vet Res 1997;58:1083–1091)

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