Congenital malformations of the thoracic vertebral column in a mature competition pony.

Thoracolumbar congenital abnormalities are considered rare in mature, performing horses. This case report describes a 14-year-old Welsh pony presented with marked epaxial muscle atrophy, mid-thoracic spinal pain, and stiffness, most pronounced during canter. The thoracic spine exhibited scoliosis, centered at T9-T10, and kyphosis. Radiography and postmortem computed tomography revealed complex congenital malformations of the thoracic vertebral column, including abnormal morphology of the T10-T12 vertebral bodies, partial vertebral fusion, a malformed spinous process, a malformed rib with associated costovertebral and costotransverse joints, and degenerative changes affecting multiple costovertebral and costotransverse joints. Given the combination of persistent ridden behavioral manifestations, safety concerns for a young rider, financial limitations, and the extent of the anatomical abnormalities, euthanasia was elected by the owner. This report highlights the importance of considering congenital thoracic vertebral anomalies as a potential contributor to chronic thoracolumbar pain in adult horses, even in the absence of neurological deficits.