Developmental variation in lumbosacropelvic anatomy of thoroughbred racehorses

Am J Vet Res. 1997 Oct;58(10):1083-91.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aging / physiology
  • Animals
  • Epiphyses / anatomy & histology
  • Female
  • Horses / anatomy & histology*
  • Lumbar Vertebrae / anatomy & histology*
  • Male
  • Pelvic Bones / anatomy & histology*
  • Sacrum / anatomy & histology*
  • Spine / physiology
  • Tail / anatomy & histology
  • Thoracic Vertebrae / anatomy & histology*