For this article, we will answer a very interesting question posed by one of our readers. Can a horse break their tongue bone?

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What is the “tongue bone”?

In short, there is no bone present in the tongue itself; but the tongue is attached to a cage-like structure made up of multiple bones, called the hyoid apparatus. So, while strictly speaking they cannot break a bone in the body of the tongue, they can fracture one to which the tongue is attached. 

All about the Hyoid

The hyoid apparatus serves to alter the position and diameter of the larynx and nasopharynx; which allows the horse to take in as much air as possible when running at high speeds as well as supporting and connecting structures inside the head and throat. It is made up of pairs of bones called the stylohyoid, epihyoid, ceratohyoid and thyrohyoid bones and a single bone called the basihyoid. The tongue is attached to the hyoid apparatus by the basihyoid bone; and is also attached to the soft tissue structures of the back of the throat or pharynx. 

The tongue itself is made up of muscles, nerves and tendon

Movement of the tongue is critical in ingesting and chewing food. But as it is attached to the hyoid process, contraction of the muscles of the tongue will alter the shape of the hyoid apparatus; something that is important during high-speed exercise. The tongue contracts to force itself downwards to stabilise and dilate the airways of the nasopharynx, maximising air intake. This mechanism for dilating the airways is the basis behind the use of tongue ties in racehorses; although artificially tying the tongue down is not as useful as the active process of tongue depression by the horse itself. 

Like any bones, those in the hyoid apparatus are vulnerable to fracture or disease

Fractures of these bones are rare and only limited reports are available in the literature about such cases. The most common site of fracture is the stylohyoid bone, usually as a result of trauma or a disease called temporohyoid osteoarthropathy  (THO) which weakens the bone. 

It is important to be aware that clinical signs can vary greatly depending on the structures that are affected by the fracture, which can include nerves and major blood vessels. In many cases of THO or stylohyoid bone fracture, the horse will have difficulty swallowing or picking up food. 

This is a painful condition and any horse that has problems eating should be assessed by a vet as a matter of urgency. In the early stages of temporohyoid osteoarthropathy, the horse may show vague signs; such as headshaking, bit avoidance, face rubbing or dysphagia. In later stages they may show signs of nerve damage (the stylohyoid bone is close to certain nerves); such as eye problems or a head tilt. 

How do we diagnose and manage damage to the hyoid apparatus?

The horse has a pair of structures in the pharynx called the guttural pouches, through which blood vessels and nerves run. Each of the guttural pouches (left and right) are divided into two compartments (inside and outside) by the stylohyoid bone. It is possible to access the inside of the guttural pouches using endoscopy in the standing horse. And the stylohyoid bone can be visualised through the thin membrane of the guttural pouch. For this reason, endoscopy is usually the first form of diagnostic imaging used in cases of dysphagia or suspected stylohyoid disease. In addition to endoscopy, radiography, CT or MRI can be extremely useful as they can provide information about all of the soft tissue structures that are likely to be affected as well as the bony structures that cannot be imaged using endoscopy. 

Some of the reported cases of stylohyoid bone fracture responded well to conservative management (rest and pain relief) and temporary dietary changes. But treatment will depend on the structures affected. There are some surgical options for cases of THO. But these are not without complications and options would depend on the individual case.

How to reduce risk of damage to stylohyoid and tongue.

Historically, it was not uncommon for vets or dentists to examine the horse’s mouth by pulling the tongue out of the way or using it to gain access to the mouth. Since the development of good equipment and adequate sedation, this is generally deemed unnecessary. Although your vet or dentist will move the tongue around the mouth during an oral examination and treatment; they will take great care to avoid pulling on it. The use of sedation also reduces the risk of the horse moving suddenly which may cause damage. 

Some of these cases are secondary to THO, which may not be possible to prevent. However, if your horse has been diagnosed with THO, without a fracture, or has undergone conservative management for a fracture, extreme care will be taken during dental examination or with procedures like stomach tubing, to prevent excessive force on the tongue. 

What about damage to the tongue itself?

We all know that horses can find unusual ways of injuring most body parts and the tongue is no exception! In some cases, horses may have quite significant damage to their tongue. For example, due to trauma from a dental fracture or a foreign body, such as prickly thorns, and show relatively few symptoms. But usually tongue injuries tend to present as difficulty eating, drooling or bleeding from the mouth. 

One of the most common causes of damage to the tongue is due to the bit or a Chifney, usually if the horse is forcibly restrained. These injuries tend to vary from a mild crush to full or partial amputation. Occasionally, the horse may bite their own tongue during a fall, this is rare, but can be catastrophic. Horses that lose part of their tongue can manage to cope reasonably well with dietary management, but it does depend on how much of a loss they sustain. 

We occasionally get asked about horses who spend lengthy periods of time sucking on their tongue. This is considered a vice and may be linked to medical problems such as gastric ulceration or dental disease, so please speak to your vet who can rule out any possible underlying causes of this behaviour. 

What to do if you are concerned?

If you are concerned that your horse has a problem with their tongue, or eating in general, please contact your vet who will be able to perform a detailed examination to determine if a problem is present. This may also include the use of further imaging such as endoscopy, radiography or CT to fully visualise the structures that may be affected. 

In summary, although there is no bone present in the tongue itself, horses can certainly develop problems with their tongue; including fractures of the stylohyoid bone to which it is attached. Such problems are uncommon but should be investigated promptly. 

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