Lumbosacral transitional vertebra and thoracic limb malformations in a Chihuahua puppy.

A three-month-old, male Chihuahua puppy with congenital absence of the distal 40% of the right thoracic limb was examined. The limb ended as a short, rounded, skin-covered stump. Radiography revealed a 40% shortened humerus tapered to a blunt end without its distal extremity. Dissection of the left thoracic limb identified luxation of the elbow joint and absence of the fourth digital pad. Alizarin-red staining and clearing demonstrated syndactylous fourth and fifth digits in the left thoracic limb and an anomalous eighth lumbar vertebra. This additional vertebra was unilaterally sacralized and constituted a lumbosacral transitional vertebra.