Below is a question that was asked on the Masterson Website Question & Answer webpage recently and instead of answering directly to the person who asked the question, we chose to challenge our in-house anatomy junkie, Lorre Mueller (as well as MMCP, Instructor, Coach and Mentor and Equine Osteopath EDO®). Lorre asked if she could write an article instead, knowing that this is a pretty common problem and that many people may have the same question.

So here was the question:

“Some horses seem to bend (or break) at c3 vertebrae along the top of the neck. Instead of a smooth arch in the neck they’ll have a bend at c3. Is this a natural bend or is this a muscle issue (some trainers say this is caused by pulling too much on the bit)?”  Ty

Hi Ty,

Thanks for your question. I have pondered this question for quite a few days, wondering how much is too much information, how can I answer this question without overwhelming the reader. However, I decided it is something worth diving into…even if it is complex. Your question is not a simple one, with only one answer. But before I can even think about trying to give you some of the “whys”, I need to first explain how these joints should function, so that I then might be able to explain some of the reasons why it may cause problems when they are not functioning properly…meaning within their full range of motion.

I am going to really go out on a limb here and be very bold, making this statement, “The majority of horses out there have this problem.” (I won’t give you exact numbers because I have not gathered that information, but I will say as an equine osteopath, I find this mobility loss at CO/C1 way too often and it is very unfortunate for the horse). With that said, you have to understand how adaptable our horses truly are…they will do whatever is necessary, like moving their bodies in unnatural ways, to give us what we want. They want to please us, through no fault of their own, other than they are so kind and pure of heart. It is our responsibility as horse owners, riders and trainers to right the wrongs.

To answer your question in the simplest terms…Is this a natural bend? NO!!! Is this a muscle issue? YES…but that is not all it is…muscles are only a small part of the issue. Is it caused by too much pulling on the bit? YES, it can be caused by this, but there are a number of other factors that can lead to this issue as well, so not all the blame can be placed on “pulling too hard”.

The OAA Complex; the Occipit (CO), Atlas(C1), Axis (C2) juncture is truly complex and there can be a number of reasons why the horse seems to “break” at C3…which is really happening more between C1 and C2 than at C3.  Here is a view of this OAA complex so you can visualize some of the things I am about to talk about:

Let’s first look at why this OAA complex is so unique and then talk about how it moves. The atlas and axis are two very different bones, none of the other cervical vertebrae are shaped like these or do the kind of motion they do. They also have no inter-vertebral discs, like the rest of the spine.


Picture above shows the occipital condyles.  Picture below is the articulation surface of the atlas which moves over the condyles of the occiput

The occiput directly articulates on the joint surface of the atlas.  The articulation between the atlas and axis is on 3 joint surfaces: 2 lateral, where the caudal surface of the atlas articulates on the cranial surface of the axis and the medial surface, where the dens of the axis articulates on the fovea dentis of the atlas.

Figure on Right:  You can see the lateral joint surfaces.  At the tip of the bone on the right shows the dens that articulate inside the atlas on the fovea dentis

This creates very stable joints (for supporting and controlling a very large head) but it also allows a great deal of motion. The horse’s greatest range of motion (ROM) comes at the upper and at the lower neck. They have this motion for really simple reasons: at the poll, for maximizing their sight of their surroundings, they are prey animals so they have the greatest ROM at the poll so they can see easily in all directions. The next spot is at the base of the neck: and simply it is because they are grazers (or pickers, so leaves from trees) and the movement at the lower neck facilitates their eating habits.

Now let’s look at the movement of the OAA complex.

Between the occiput and the atlas, the joint is a bi-condylar, synovial joint with 2 separate joint capsules (one on each side). The occipital condyles of the skull move (translate) under the articulation surface of the atlas. It should perform a roll, slide motion when asked to translate in its ROM, which consists of dorsoventral flexion and extension, side-bending (lateral flexion) with a slight translation of the occiput in the opposite direction during the side bending, and rotation, all in varying degrees, meaning some of these motions have more range than others, for instance, the dorsoventral motion of flexion and extension is the horse’s biggest ROM at this joint, with extension being the biggest. (For really exact measurements you can refer to some of the studies done by Dr. Hilary Clayton…they are pretty easy to google and too many of them to cite them all here, but here is one to get you started:

More often than not, the horse has lost some of the ROM of the joint between CO and C1 and to compensate for this loss of motion they move between C1 and C2 (breaking) and this is not a good movement for our horses. We want them to move freely and correctly at CO/C1 (where their greatest ROM already exists). Here is an exercise that you can do, to try and help you visualize the motion the horse should have here (see pictures). Make a fist with your left hand (this is the occiput), out in front of you at eye level (your elbow will be the nose of the horse and should be out to your left), cup your right hand completely over your fist (your right hand is the atlas).  Now, raise your left elbow and let your fist (occiput) roll, slide under your cupped hand (atlas), this is an extension of this joint.  Now lower your elbow, this is a flexion of this joint.  Now bring your elbow towards your body, this is a side bend to the left, let your fist slide under your cupped hand in the opposite direction. You might notice that your cupped hand (the atlas) naturally wants to slide to ventral (downward) when the occiput translates away. Try this to the opposite side as well, move your elbow away from your body and notice what happens. This really mimics the movement that is happening in this joint. Unfortunately, for many reasons (that I will cover further on) the horse will start to hinge at this joint, instead of a roll, sliding motion.



So now let’s do this exercise with our hands again. Put them back out in front of you just like before, now what I want you to do is make it a hinge joint. Brace the knuckles of your fist in the groove of the knuckles in the palm of your right hand, now move your left elbow up and down (like flexion/extension of the horse’s head) but don’t let it roll/slide, make it hinge…do you notice when you lift your elbow (extension), it makes your atlas drop, so the horse is moving this juncture like a whole unit. When you go to flexion (which is what they do when we ask them for collection), the whole UNIT rises…so “breaks” between C1/C2, or they may try to flex more between C2 and C3 so some may call this the “break” point. All that we need to remember is that this is NOT a natural or correct bend when the movement is at either C1/C2 or at C2/C3, and not between C0/C1. The horse is trying their best to give us the flexion we are asking for but since they cannot move correctly at the poll, they have to make up that loss of motion at CO/C1, somewhere else. You can imagine, if this is what is happening, the poll is no longer the highest point in the neck.


C2:  Do you see how it is the highest point in the neck?  Do you notice the extension of the joint between c1/c2?  now imagine asking this horse to flex, they would flex at the same place, between C1/C2, forcing the dens that sits inside the atlas to dorsal and dangerously close to touching the spinal cord

This is a bad movement for our horses. The joint between C1/C2 is a very unique joint, and allows for VERY little flexion/extension…it is a joint of rotation. (For all those MMCPers and Masterson students out there, this is the “laying flat” Jim talks about when doing LCF, because they cannot side bend (flex laterally) at CO/C1, and we are asking them to do just that, they have to then rotate at C1/C2 instead to try and get that side bend and thus they lay flat). Now let’s look at the joint between C1 (atlas) and C2 (axis). I am going to have you create this joint with your hands out in front of you again. With your left hand, make a loose fist so that your thumb is pointing directly away from you, but make your thumb and pointer finger touch so that you create an “O”. With your right hand, make a fist but stick out your pointer finger, place the tip of your pointer finger in the “O” of your left hand about up to the first joint of that pointer finger…this is called the dens of C2.



Now, rotate your left hand around your pointer finger. This is how the atlas rotates around the dens of the axis. Try flexion/extension, visualize the spinal cord running through that hole on top of your finger (I should have made my finger touch the bottom of the “O”), can you see how the dens (the tip of your pointer finger) may come in contact with the spinal cord if this is where they are flexing instead of doing this motion where they are supposed to do it; CO/C1. There is also a ligament that attaches the dens to the atlas, the transverse ligament. Flexion/extension of this joint puts undue strain on this ligament, not to mention the pressure it puts on the spinal cord itself, remember this joint only does a very small movement in this dorsoventral direction, its main movement is rotation around the longitudinal axis of the vertebrae. If the horse cannot move properly at CO/C1, it will begin creating some very dangerous situations for the horse’s overall health and well-being.   I recently read an article by Mark Rashid that addresses this concern. In the article he talks more about the over use of lateral flexion and the problems it causes at C1/C2 but you can make the same arguments for the over use of dorsal flexion to create these same problems. Here is the link to the article…it is worth the read.

Now that we have the mechanics of these joints in our minds, let’s look at some of the reasons we may have horses with mobility problems at CO/C1, that are compensating for this mobility loss at C1/C2.

Here is a list of many reasons a horse can have mobility loss at CO/C1:

  • Are the teeth floated properly to ensure proper alignment and occlusion? Are the TMJ’s being affected by any malocclusions or misalignments of the teeth and/or mandible? Is any of this causing problems on the hyoid apparatus (the bones at the base of the tongue) that attach to the temporal bones? Any problems on the TMJ will result in problems at CO/C1 because the temporal bones and occipital bone influence each other and also because of how the mandible and temporal bones muscularly attach to the poll and neck (and shoulder).
  • Is it a sacrum problem (yes, I am asking, is it a hind end problem)? The sacrum is directly attached to the occiput (it is the only places the spinal cord actually attaches within the vertebral column…at the sacrum and occiput). It is also directly attached by the nuchal ligament attaching at the occipital protuberance which then turns into the supraspinous ligament along the back to attach on the sacrum. They directlyinfluence each other.
  • Is it a foot problem? Imbalances in feet will cause shoulder and/or pelvis problems, which will influence the TMJ…which will influence the poll…do you see how it goes round and round. Are you starting to see how the whole body is connected and something far away from the problem can be the cause?
  • Is it a visceral problem (an organ problem)? All information from the organs gets to our central nervous system in two ways: through nerve pathways to our sympathetic border trunk (which cause localized problems, meaning in the areas of the spine where those organs report their information to) and through the vagus nerve, whose pathway is to the brainstem, through the jugular foramen, which is made up of the occipital, temporal and sphenoid bones of the skull. Here lies the problem: there is a ganglion just before it enters the skull called ganglion nodosum, it has a side branch that innervates (provides nerve supply) to the joint capsule of CO/C1. If this ganglion is aggravated or overstimulated with information coming in from the organs it will cause problems for the joint capsule, becoming a source of the loss of mobility at this joint. YIKES!
  • Is it a training issue? Is the horse being forced into a frame that is causing the loss of mobility? Are any of the issues mentioned above causing problems for the horse, that in turn cause training issues for us humans and instead of us searching for the cause of their evasion, we just ask harder? Or use more aides to get the results we are after like tie-downs, draw reins, etc.? In these cases, the horse just tries to evade and get away from the pressure and/or pain. We unfortunately, by our practices, force the horse to adapt and use his body in unnatural ways.
  • I am sure we can list many more reasons as well. I bet we could include saddle fit, nutrition (or lack there of), injuries, stress, lack of conditioning and/or strength to do the things we are asking of the horse…I am sure I could go on.

Can you now understand why in the beginning I said this was not a question with a simple answer and that there could be many reasons for “why” they are “breaking” at C1/C2. As you can see there may be reasons for the loss of mobility that we may not have considered or even have the knowledge to consider. I am hoping that I was able to provide you with some deeper knowledge of this part of the horse’s body, and in doing so, provided us all with a deeper understanding of the horse as a whole. It is my hope for the horse, that in trying to seek answers, we start to see that to solve these problems it is of utmost importance to look at the horse as a whole: mind, body and spirit.

How can you help your horse if you think there are problems of mobility loss at these joints? Seek the help of a good osteopath or chiropractor (if there is no osteopath in your area) so that they can assess your horse, as a whole (I cannot stress this point enough) and make a determination as to the loss of mobility at the joints; C0/C1 and C1/C2 and well as the rest of the horse. They may ask for the assistance of your veterinarian, if they determine the loss is significant. They may want x-rays done so that the veterinarian and the osteopath (or chiropractor) can determine if there are any structural changes to the joints. If the veterinarian determines there are no structural changes, the osteopath or chiropractor can make the necessary adjustments and restore mobility. Then of course you can follow up with Masterson Method bodywork to help release any muscle tension that had accumulated along with the restrictions of movement.