• Equus-Soma

    Equine Osteology & Anatomy Learning Center

     

  • Aiken, SC

    info@equus-soma.com

     

  • Waldoboro, ME

    207-542-6132

  • ECVM: A Three-Dimensional Point of View

  •         Our recent publication (May-Davis et al., 2023) describing the morphological variations of the sixth cervical vertebrae (C6) in ECVM horses, includes a grading system based on the degree to which bone is missing from the ventral processes.  The grades are explained in the paper using photographs of representative bones from the author's cumulative dataset (N=76). 

  • References & Publications
    CLICK HERE

  • To expand on the understanding of ECVM morphology we present here 3D renderings of the bones from our Equus-Soma collection, beginning with C6.

  • Review of C6 ECVM Grading System

           The photo to the left is a ventral view of the same C6 as the 3D model in the right sidebar (Apollo).  Note the right and left "ventral processes".  In the normal condition, these bilateral, tube-like bony projections extend the full length of the vertebral body of C6, and C6 only.  The six other cervical vertebrae do not possess these structures in the normal state.

           Each ventral process is further differentiated morphologically, into a cranial ventral tubercle (CrVT) designated by #1 and #2 in the 3D model; and a caudal ventral tubercle (CVT) designated by #3 and #4 on the 3D model (also see photo below left).

           The demarcation between the CrVT and the CVT is identified as the region where the caudal border of the transverse process joins the vertebral body (green dashed line in photo below).

            This is best understood by rotating the 3D model of the normal C6 (at right) and studying the locations of #6 and #8. These mark where the caudal lamina of the transverse process joins with the dorsal edge of the ventral tubercle.

  • Viewing the 3D Models

    IMPORTANT:  **These 3D models are for on-line viewing only. The files cannot be downloaded.**

            Click on the 3D model of interest below.  The blue cube in the bottom left corner will take you to the model's page on the Equus-Soma Sketchfab account (in a new window).  To see the model in full screen, click/tap on the double arrows in the lower right corner. 
           To move and rotate the model, grab it with the mouse or fingers and drag around. If you use a mouse with a scroll wheel, this will zoom in and out.  Escape to exit full screen.  On a tablet, two fingers to zoom, swipe down to exit full screen.
           
           Numbers on the model, indicate annotations that explain the structure. Click/tap on the number and a box with the description will open.


  •        The congenital malformations to the C6 vertebrae involve faulty embryological development of portions of either the right, the left, or both ventral processes.

           Prior to our current study, the malformations were described in general as the "left, right or both caudal ventral tubercles being absent or missing". 

           Examining the morphology of each bone more closely, we found that the quantity of missing bone can differ between the left and right ventral processes, even within a single horse. 
           This led to the development of a grading system that identifies the extent of the absence in equal quarterly increments.

  • Apollo
    C6 - Normal Ventral Morphology 

  •         For grading purposes, we visualized dividing the CrVT and CVT of each ventral process into relatively equal quarterly increments (above photo). As the grade number increases from 1 to 4, so does the amount of absent bone from the tubercle in the caudal to cranial direction.  For example, when an absent caudal ventral tubercle (aCVT) displays a grade 1, it indicates that 1/4 of the CVT is absent at the caudal-most region of that tubercle (see 3D of Mikey below).  At the opposite extreme, when an aCVT is assigned grade 4, the entire CVT is missing as will be illustrated in several of the 3D models.

  • What is the significance of the paired ventral processes unique to C6?
    Both the cranial and caudal tubercles serve as anchor sites for the longus colli muscles, important for stabilization of the lower neck region. See this paper for details.

  • Examples of Unilateral C6

  • Grade 1 Left aCVT (1/4)
    C7 - no transposition

    Mikey

  • Grade 4 Left aCVT (4/4)
    C7 - no transposition

  • Grade 4 Left aCVT (4/4)
    C7 - left incomplete transposition

  • Grade 4 Left aCVT (4/4)
    C7 - left incomplete transposition

    Luna

  • Grade 4 Left CVT (4/4)
    C7 = incomplete left transposition;
    left arterial foramen

    Rosewood

  • Grade 4 Right CVT (4/4)
    C7 = no transposition


    Skylar

  • **Something to think about while viewing the ECVM C6 vertebrae**

           The ventral processes on C6 are attachment sites for the tendons of very important stabilizing muscles of the neck, the longus colli.
           If a portion or all of the CVT is missing, where do the tendons attach? and what might be the consequence(s) of these altered attachment sites?
           
           May-Davis and Walker (2015) described alterations to the l. colli along with other associated soft-tissues (PDF).

  • Examples of Bilateral C6

  • Grade 4 Left aCVT (4/4)
    Grade 1 Right aCVT (1/4)
    C7 - complete left transposition

  • Grade 4 Left aCVT (4/4)
    Grade 1-2 Right aCVT
    C7 - left transposition;
    no arterial foramen

    Edge

  • Grade 4 Right CVT = 4/4
    Grade 3 Left CVT = 3/4
    C7 no transposition; Left rud rib

  • Grade 4 Left aCVT (4/4)
    Grade 4 Right aCVT (4/4)
    No transposition

    WhoZat

  • Grade 4 Left aCVT (4/4);
    Grade 4 Right aCVT (4/4)
    C7 - incomplete bilat transpositions

    Trudy

  • Grade 4 Left and Right aCVT
    C7 - asym bilat transpositions
    bilateral arterial foramina
    Right rudimentary 1st rib, fused

    Forbes

     

  • Grade 4 Left aCVT (4/4)
    Grade 4 Right aCVT (4/4)
    C7 - incomplete right transposition

    Chester

  • Grade 4 Left aCVT (4/4)
    Grade 4 Right aCVT (4/4)
    C7 - complete bilateral transpositions
    bilateral arterial foramina

    Ditty

  • **Something Important to think about while viewing the ECVM C6 BILATERAL vertebrae**

           Examine the 3D models below of two different horses (Warrior and Swt).  The C6 of both have left and right grade 4 aCVTs, i.e., bilateral, completely missing caudal ventral tubercles.  Now look at the C5 for each horse. What do you see?  It's pretty obvious, right? 

    In the grade 4 bilateral variation, C6 has acquired the morphological identity of C5.

    Think about the FUNCTIONAL ramifications in the lower neck region!

  • Grade 4 Left & Right aCVT (4/4)
    C7 - bilateral transpositions;
    bilateral arterial foramina

    Warrior C6


  • Warrior C5

  • Grade 4 Left & Right aCVT
    C7 - complete bilateral transposition
    bilateral rud 1st ribs - fused

    Swt C6


  • Swt C5

  •        PLEASE NOTE:  Our paper described not only the grades of absent CVTs, but in some horses we found that the missing tubercle extended further cranially to involve portions of the CrVT as well.  Therefore the paper also includes grading for the aCrVT.  Since the bony changes on the CrVT are more subtle and not easy to label in the 3D models, they will not be identified here.  Please refer to the publication for full details. 
            Also, the 3D models shown here are of C6 only (plus two C5s).  We are currently finalizing a manuscript on the morphological variations of C7, but until that paper is published, I will refrain from sharing links to the C7 3D models ... at least for now.