Stress in the TMJ
As a horse rider/owner you may have heard your riding instructor or therapist refer to the “TMJ” and the important role it plays as part of your horse’s anatomy. But what is it and what does it do?
Well, first of all, let’s identify where it is…
The TMJ “Temporomandibular Joint” is the point where the lower jaw (Mandible) connects to the upper jaw (Maxilla) through the temporal bone of the horse’s skull. For those who are unfamiliar with the TMJ and are trying to identify it for the first time, it is easiest to spot when your horses is chewing.
Take a look at the photograph to the right, highlighting its position. There are two TMJs, one on either side of the head.
And the next question… what does it do?
The main purpose of the TMJ is to open and close the horse’s mouth, for example to chew food, to bite down on something hard and to accept a bridle with bit. Therefore, it works in many planes (directions) allowing the horse to open its mouth up and down and side to side in order to chew.
Causes of stress in the TMJ
As with any other joint, the TMJ can become inflamed, or infected resulting in pain. Often overlooked by many horse owners/riders, an understanding of the TMJ is critical given that the contact you have with the horse’s mouth via the bit creates force on this joint which can cause discomfort. A downward force increases this pressure, which is one reason why draw reins can be so problematic.
Additionally, direct trauma from a fall or collision with an object such as a stable door or trailer/horsebox compartment, can cause stress and pain and the joint can suffer from degenerative diseases such as arthritis. Again, many of us are familiar with the term “arthritis” but only really consider this in connection with the joints of our horse’s limbs (as these sustain considerable wear through riding), and we do not think to consider the impact our rein contact has on the TMJ and the potential for degenerative disease in this area.
Possible causes of TMJ discomfort and pain
There is no definitive answer to this question, and some causes may surprise you. For example, the simple act of biting down on a hard object or opening the mouth wide, can cause subluxation (partial dislocation) of the TMJ – considerations here for possible causes include feeding a large carrot that has not been cut down or excessive force used with the speculum during a dental examination, perhaps if the horse is resisting.
Overuse and poor biomechanical function (forced outline) is a very common cause in the ridden horse. Where a horse is not in a natural outline (achieved by true engagement), but is working in a forced outline by either the rider’s hands or a set of draw reins, or not receiving adequate rest breaks during schooling sessions to allow for stretching and relaxing through the TMJ, neck and poll (The TMJ,. neck and Poll are closely linked, which I will explain in a moment).
Poor bridle fit (buckle placement). I have mentioned in past blogs about the importance of correct bridle fit (see https://www.equine-therapy.co.uk/blog/thehorsesback) as although there is now a much greater awareness about correct bit and bridle fitting, many riders/owners focus primarily on saddle fit. The TMJ is rich in nerves so the buckle positioning of cheek pieces and the noseband is critical to avoid pressure and friction on this sensitive area and the bit itself needs to be correctly fitted to prevent excessive downward pressure during rein contact, which increases force on the TMJ.
Take a look at the photographs below and see how on the left hand image, the buckles of the bridle are sitting directly on top of the TMJ, which could cause irritation to the nerves resulting in discomfort, inflammation and swelling. Whereas, on the right hand image, the buckles are sitting well below the Temporomanibular joint.
The connection with other muscles
The TMJ has links with other anatomy within the horse’s head and neck, in particular the Poll and the Brachiocephalic. These elements of the muscular skeletal system (MSK) share muscle and nerve connections. The brachiocephalic attaches at the poll and runs down the horse’s neck inserting at the humerous on the front the forelimb, therefore tension in the TMJ can cause tightness in both the poll and the neck and affect gait, as the brachiocephalic plays a direct role in protraction of the forelimb.
The Brachiocephalic Muscle
The TMJ, Poll and Brachiocephalic muscle are all interconnected so tension in one can cause stiffness, discomfort, or referred pain in another.
Signs and symptoms of TMJ discomfort
This list is not exhaustive, but below are a few of the most common signs of discomfort within the TMJ:
Heat or swelling
Resistant to touch or to be bridled/head shy
Head tossing
Tilting of the head during ridden work/uneven contact
Reduced flexion and extension of neck, lack of bend or resistance to work
Shortened stride
Difficulty with collection work
Napping, bucking, rearing etc.
Sticking tongue out
Avoiding hand contact with the mouth
Decreased appetite or difficulty to chew food/dropping food when eating
Diagnosis and treatment
Obviously, the above symptoms can be indicators of numerous other conditions, so if your horse is expressing any or a combination these types of symptoms, it is important to have a Vet carry out an examination to identify the root cause and to see if there are any underlying conditions that need to be treated.
The Vet may recommend rest, ice and gentle massage to reduce any immediate inflammation and swelling or, as with any other joint, they may decide to perform further tests such as nerve blocking, joint fluid analysis, X-Rays, CT or ultrasound, to investigate further for more serious conditions to establish a comprehensive treatment and recovery plan.
Where there is no serious underlying condition and tension has just built up in the TMJ through overuse or poor biomechanical function, equine massage therapy can help to relax the muscles around the TMJ. Combined with a tack check and review of your current riding routine, this can be a highly effective management strategy. A qualified Equine Massage Therapist will be able to use a variety of techniques to relax and relieve tension, not only in the TMJ, but in the connected muscles groups of the poll, neck and forelimb.
Well that’s the TMJ in a nutshell and I hope you’ve enjoyed my latest blog. The takeaway from today’s ramblings? Don’t underestimate this small yet powerful joint in your horse’s body and remember to be vigilant for small cues that may indicate tension in this area so that any small niggles can be resolved quickly, with early veterinary diagnosis, before they become chronic.
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Thanks for reading and sharing and I look forward to catching up with you again soon! In the mean time, why not check out some of my other blog posts.