The Atlas: An Interview with Dennis O'Brien, DC
NHM: What is the importance of the atlas functioning
Dr. O'Brien: The atlas is the most freely moving segment in the spine of the horse - where the base of the skull meets the spine. Atlas rotation allows the horse to turn the head sideways and to reach way back to scratch the hindquarters. A flexible neck is important too, but much of it is dependent upon rotation of the atlas.
The importance of proper function in this area is simply this: inside the atlas is the brain stem. The brain stem is like an electrical junction box that connects all the signals from the brain and routes them to the proper pathways down through the spinal cord. Then the flip side of that is that everything down in the lower part of the body is routed to the correct part of the brain going upstream. For example, with lameness, a lot of times there are horses that look like they're off in the legs or the hips when where the problem really lies is in the 'wiring' from the atlas or that side of the brain stem. Each of the rear quarters of a horse preferably operates 50/50. However, if you have an atlas subluxation, the wiring down to the muscles that run the rear quarters is affected and that nerve signal is going to get distorted - not so much in the rear quarter, but up in the brain stem. So now we have a rear end that goes 60/40, or 70/30. That configuration turns into a horse that crossfires or can't pick up both leads.
Now if you did a cross section of the brain stem, what you would find is the outside tracks (the outer nerves) are all motor tracks. Picture it like a big phone cable, made up of a lot of little wires, so the outside wires are motor tracks. So if the atlas gets distorted in its relative position, between the occiput and the axis, the brain stem is going to get distorted. And consequently the nerve tracks will get distorted which will deliver a faulty signal down below. The nerve signals need to get through there clearly.
NHM: How can a subluxation of the atlas be determined?
Dr. O'Brien: Motion palpation can pretty much determine that, and the range of motion. If the horse can turn its head to the right correctly, sort of upwards and to the side, but not to the left, it's most likely indicative of a problem with the atlas. And sometimes under saddle, a horse will cock its head to the side; that's a pretty good indicator, too.
NHM: If a horse has trouble moving its head in that
particular area, can you tell if it's a neurological problem causing pain,
or if it's soft tissue restriction?
Dr. O'Brien: I don't think you're going to have one without the other. They will be like two peas in a pod. You probably won't get ligamentous restriction; the job of the ligament is to limit the motion at the joint. What you're going to have restrictions in is the muscles that move that joint and their tendons, and the joint capsule. If we've altered the wiring in that area, then we'll get a lot of nerve hyperfacilitation, in that the muscles around that area will get stuck in the "on" or contracted position.
NHM: What exactly does the "on position"
Dr. O'Brien: It means that even if you don't want it to happen, you'll get a local muscle spasm. A muscle spasm is nothing more than probably 10-20% of the muscle fibers firing, even though you're trying to say to click off, but they don't; they're just stuck in the on position. And after a while, you're going to build up a lot of metabolites (i.e. lactic acid) in the muscle and it's going to get fatigued and start firing off pain receptors.
NHM: What causes atlas subluxation?
Dr. O'Brien: Atlas subluxation can be caused by an uneven bite. Horses don't chew like we do - they have a figure-8 type of bite. If you have some asymmetries caused by a wave in a mouth or an unopposed tooth or other dental issues you're going to change the mechanics of the TMJ, the temporal mandibular joint, and when you change that you effectively change the junction between the occiput and the atlas. If there are upper cervical problems I will always, always check the bite on the horse. If they have a really bad bite, an adjustment is not going to hold. So they need to take care of the bite first and then clean up the upper neck or do craniosacral work or whatever needs to be done. Dentistry first is important.
Improper bits and bridles, and the misuse of certain bits such as those with long ports, are other causes of subluxation. Pulling back when tied is another major cause. If you're going to tie a horse that isn't confident or properly trained for that, it's a good idea to tie him to a big inner tube. If he pulls back, there will be some give. Hay racks could possibly play a part in neck problems. I do not advocate hay racks because the best eating position for the horse is with the head down. That's just part of general good horse management.
NHM: Can carrot stretches do harm?
Dr. O'Brien: You're probably not going to do harm to a horse by sensibly stretching him out.
NHM: How breakable is the atlas?
Dr. O'Brien: It's like a Swiss watch. It's somewhat fragile, and it's a very important area. It's the most freely movable spinal segment and, like many moving parts, is very delicate. Its proper function is vital, and that's why you need to get someone that's properly trained in chiropractic.
NHM: How does one go about finding an equine chiropractor?
Dr. O'Brien: If you see that you have a problem, and want to choose a chiropractor, just because someone has taken a course or is licensed doesn't mean they are competent. This is true for any profession. Make sure they have a broad knowledge of horsemanship, and that they can look at not just an atlas but a whole horse, under saddle, and can evaluate a horse, rider, and so on - conformation, saddle fit, diet, training program, hoof care, etc. Certainly get references. Even being certified by the AVCA does not guarantee proficiency, and a licensed chiropractor may or may not know anything about horses. But the AVCA is a good place to start looking. Avoid cowboy chiropractors, that is, a layperson who professes to be a chiropractor. If someone is not licensed and properly trained he or she can really hurt an animal.
Natural Horse Magazine thanks Dr. Dennis O'Brien for this interview.
This article is for informational purposes only and is not intended to replace veterinary or other professional care.
Dennis O'Brien, DC is a chiropractic physician, an educator, and a horseman residing in LaCenter, WA. He is certified by the American Veterinarians and Chiropractors Association and is a graduate of Western States Chiropractic College, Southwest Texas State, and Oklahoma Horseshoeing School. Dr. O'Brien served as team chiropractor for the Brazilian Equestrian Team in the 1996 World Championship and 1997 Pan American Championship. His years of equine experience also include training, conditioning and competing in endurance riding, and he is currently the coordinator for the International Alliance for Animal Therapy and Healing (IAATH) 2001 Conference. Dr. O'Brien can be reached at 360-263-6359.
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