• Aiken, SC

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  • Equus-Soma

    Equine Osteology & Anatomy Learning Center

     

  • Waldoboro, ME

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  • What do the Equine Complex Vertebral Malformations (ECVM) Look Like?


              Equine Complex Vertebral Malformations may involve C6 with or without C7, the 1st and 2nd sternal ribs, as well as the soft tissues that attach to these locations.  The malformations are a product of abnormal gene expression during embryonic development.  Therefore they are considered to be congenital (present at birth). ECVM is also believed to be hereditary (May-Davis, 2017).

  • References & Publications

    CLICK HERE

  •           A number of variations or combinations of the malformations have been reported.  For example, C6 may develop with one ventral tubercle shorter than the other, or the caudal end of one tubercle may be missing.  Sharon May-Davis (2014) termed this a "C6 malformation" (i.e., C7 is not involved and develops normally ).

              A second scenario is when all or just the caudal end of one tubercle does not develop on C6 but instead appears on C7.  Sharon May-Davis calls this a "unilateral transposition".

              A third variation of this developmental snaffu is that BOTH ventral tubercles fail to develop on C6 and end up developing on C7.  Sharon calls this variation a "bilateral transposition".

              In some horses afflicted with the cervical malformation, one or both of the 1st sternal ribs may be missing or underdeveloped. Sharon also published a paper on the 1st sternal rib malformation (2017).

              Another anomaly is the unilateral or bilateral addition of an arterial foramen (foramen = opening, hole or passage) on C7 when normally there are none. The arterial foramina provide a channel through which the vertebral artery & vein pass along the neck (Sisson & Grossman, 1975).

              Extreme changes in normal morphology of the vertebrae will affect the attaching musculature (longus coli) which can lead to disruption of normal balance and biomechanical function of the horse's neck, thoracic sling and ultimately through compensation, the whole body.

              As mentioned previously, you are encouraged to download the pertinent publications as they contain more detailed information about all of these aspects of ECVM.

  • "Petey" - 23 year-old Thoroughbred with "normal" cervical morphology

    Petey was my (lower level) event horse and first skeleton to be exhumed.
    Read about Petey's story here.

    CLICK ON ANY IMAGE TO ZOOM IN


  • Ventral view.
    Note the left and right ventral tubercles (asterisks) are of relatively equal lengths (yellow arrows).


  • Left ventro-lateral view.
    Asterisks indicate the ventral tubercles.

  • Ventral view.
    Note the absence of ridge-like ventral tubercles, but the presence of 2 smaller tubercles replacing the ventral crest (arrows).


  • Ventral view.
    C6 and C7 vertebrae adjoined at the intervertebral joint.

  • "Mikey" - 12 year-old Thoroughbred eventer

    After Petey, Mikey became the second full skeleton in our collection.  You can read Mikey's story here.

              Mikey's C6 looks almost normal except that the left ventral tubercle is truncated relative to the one on the right.  Some might question if this falls into the ECVM category of a "unilateral malformation of C6" (C7 is normal).  Or, is this merely a morphological variation that would not present with clinical problems?  Either way, I believe it may have contributed to some of Mikey's "issues" because his owner reported that he was always a "difficult" horse with intermittent lameness and sacroiliac discomfort.

    CLICK ON ANY IMAGE TO ZOOM IN

  • Ventral view.
    Notice the difference between Mikey's ventral tubercles (yellow asterisks) and those of Petey (above).  The arrows indicate that the left ventral tubercle is not the same length as the right.
    Is this asymmetry significant enough to be considered a "malformation" or a "variation"?


  • Caudal view.
    (Looking toward the head)
    Arrows indicate asymmetry between the ventral tubercles.

  •  

    Ventral view.
    Normal C7. Arrows point to the pair of ventral tubercles.


  • Ventral view.
    C6 and C7 vertebrae adjoined at the intervertebral joint.
    Note the difference in length of the ventral tubercles (arrows) on C6.

  • Thoroughbred Mare - mid-20's

    Below is an example of a "left unilateral malformation" of C6, where the caudal half of the left ventral tubercle is completely "missing".  C7 has normal morphology.

     

  • Ventral view.
    The left ventral tubercle (red asterisk) is not fully developed. The yellow oval indicates where the caudal part is missing. Compare this to the fully developed right ventral tubercle (yellow asterisk & arrow).


  • Caudal view    .
    The right ventral tubercle (yellow arrow) is present whereas the left is missing.


  • Left ventro-lateral view.
    Normal C7.  Arrow indicates the ventral tubercles.

  • Ventral view.
    C6 and C7 adjoined at the intervertebral joint.
    Red asterisks indicate the cranial end of the right & left ventral tubercles.
    The yellow oval shows where the caudal region of the left ventral tubercle is missing.


  • CLICK ON ANY IMAGE TO ZOOM IN

  • Warmblood gelding - 9 years-old

                Below is an example of a "left unilateral transposition", where the caudal part of one ventral tubercle on C6 is relocated to C7 during development.  The other ventral tubercle is normal.
                It is difficult to envision in the 2-dimensional photographs, but when C6 and C7 vertebrae are assembled so that the spinal canal is aligned, there is a "twist" to the alignment of the ventral surfaces of C6 and C7.  Where there is asymmetry in the skeleton, the associated musculature will have to adapt  (May-Davis, 2015).

    This fellow was euthanized because his behavior had become violent.

  • Ventral view.
    The yellow asterisk indicates where the caudal ventral tubercle on the left side of C6 should be.

  • Caudal view.
    Another view.  Clearly, the right ventral tubercle (yellow arrow) is present whereas the left is absent.

  • Left ventro-lateral view.
    Arrow points to normal ventral tubercles.
    Oval indicates prescence of the caudal ventral tubercle that was supposed to have developed on C6.

  • Ventral view.
    Yellow arrow points to the ventral tubercles along the midline of C7.
    Oval indicates the caudal ventral tubercle that was supposed to have developed on C6.
    Red arrow shows  unilateral arterial foramen on the left side.

  • Cranial view.
    (looking towards the hind end)
    Yellow arrow shows the transposed caudal ventral tubercle on the left side only.
    Red arrow indicates a unilateral arterial foramen.

  • Ventral view.
    C6 and C7 adjoined at the intervertebral joint.
    Asterisks indicate the cranial ends of the right & left ventral tubercles.
    The yellow oval shows where the caudal region of the left ventral tubercle is missing.
    Yellow arrow points to where the caudal ventral tubercle was transposed onto C7.


  • CLICK ON ANY IMAGE TO ZOOM IN

  • "Warrior" - 10 year-old Friesian

               Warrior was a developmental train wreck but this did not become evident until we retrieved his bones.  His owner reported that he never showed any unusual musculoskeletal issues and was euthanized due to colic.   Needless to say it was a huge surprise to discover that Warrior had:

    - the "bilateral transposition" of the vertebral tubercles from C6 to C7,
    - bilateral arterial foramina on C7, and
    - a rudimentary 1st sternal rib.

  • Ventral view.
    Ovals mark the total absence of both left and right caudal ventral tubercles from C6. In fact, the morphology of C6 looks almost identical to that of C5 which caused some temporary confusion during the dig!

  • Ventral view.
    Arrows point to both ventral tubercles that were transposed from C6.

  • Ventro-lateral view.
    Arrows point to both ventral tubercles that were transposed from C6.

  • Ventral view.
    C6 and C7 adjoined at the intervertebral joint.
    Ovals mark the total absence of both left and right caudal ventral tubercles from C6.
    Arrows point to where both left and right caudal ventral tubercles were transposed onto C7.

  • Cranial view.
    (looking towards the hind end)
    Yellow arrows show the bilaterally transposed caudal ventral tubercles.
    Red arrows indicate bilateral arterial foramina.

  • Cranial view.
    1st pair of sternal ribs.  The right rib is normal. The left rib is extrememly truncated.

  • Cranial view of normal pair of first ribs. Showing attachment to the 1st thoracic vertebra and sternum.
    From Sisson & Grossman (1975).

  • Example of "Bilateral 1st Sternal Rib"

  •  

                The images to the right are of a 1st thoracic vertebra (T1) that was found during a random search for bones, meaning we do not know anything about the horse from which this came.

                Nevertheless, this is a great example of a bilateral rudimentary 1st rib, both ribs being fused to the costal facets which is not normal (arrows).

                For a lot more information on the rudimentary 1st rib, associated soft tissue attachments and ramifications of this ECVM see May-Davis, 2017.

  • Cranial view.

  • Left Craniolateral view.