Congenital Malformations of the First Sternal Rib (PDF)
Updated: Jan 14, 2021
Author: Sharon May-Davis Published: Journal of Equine Veterinary Science 49 (2017) 92-100
Abstract (click on the link above to download full article):
During the dissection and skeletal examination of 151 horses, a congenital malformation (CM) of the ﬁrst sternal rib that inﬂuenced the aperture of the Thoracic inlet was noted in six horses. The presentation of this CM was variable between horses in gross anatomic appearance; notably, an absent ﬁrst sternal rib, biﬁd tuberculum costae, biﬁd sternochondral articulation onto the sternum, ﬂared shaft, normal ﬁrst sternal rib inserting onto the cranial branch of a biﬁd sternochondral articulating second sternal rib, straight costal shaft, and an articulating rudimentary tuberculum costae with a ligamentous extension replacing the bony shaft and attaching to a rudimentary sternochondral articulation onto the sternum. Of the 151 horses examined, the CM of the ﬁrst sternal rib was restricted to 6/60 Thoroughbred horses, and only in those that were affected by either the unilateral or bilateral transposition of the caudal ventral tubercle from C6 onto the ventral surface of C7. The normal anatomic presentation of the thoracic inlet was altered, along with associative musculature including neurological pathways. These CMs are likely to produce clinical and functional ramiﬁcations of the thoracic inlet, thoracic limb, and thoracic viscera, with the probability of altering postural and locomotive function as noted in four horses demonstrating the CM.