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Ever since my first whole horse dissection with Sharon May-Davis I have been fascinated by this little, yet important structure within –not as the where the name presumes - the legs of the horse.

Why I am so fascinated by it? Not because I have a dirty mind (no idea who invented the term), but because I had never heard of it before. I was familiar with all sorts of tendon injuries from both experience as well as studying the subject intensively. Yet, this was completely new to me and I am guessing that at least 80% of the people reading this blog have never heard of this as well. So how come?

Well, simply because it ain’t in equine anatomy or biomechanics textbooks. Sharon told me that over the years, she had ONLY found in 1 (!!) textbook ever. And yet it is very important.

The vagina fibrosa is located in both the front- and hindlegs of the horse, a little under the fetlock. Its structure resembles to fascia. It functions as a ‘check-ligament’ in the sense that it limits, and therefore protects, an extreme range of motion of the superficial flexor tendon and the deep digital flexor tendon. It keeps the tendons ‘together’ as without it, the tendons would have no support and could move in all kinds of (extreme) hypermobile directions.

And yet, this is exactly where many modern domesticated horses suffer. I often see horses moving with fetlocks sinking into the ground (suspensory ligament disease) or moving in an extreme extension of the hoof in an unnatural way and sometimes even doing a ‘weird wobble’ around the area of the fetlock joint. This indicates that the vagina fibrosa is not able to perform its function properly. I feel honoured and fortunate that I have been able to attend multiple dissections by Sharon May-Davis. But in all dissections I have participated in so far, the vagina fibrosa was ALWAYS either inflamed or damaged in at least the frontlegs. It is such a small structure, but when it can’t function properly anymore, it affects SO MANY other structures in the body. Again, EVERYTHING is so interconnected that the disfunction of this little structure could lead to horses complete biomechanics to be out of balance.

Now what can be the causes of this?

- Congenital. A lot of horses are BRED with hypermobile movement. They already show this way of moving from a very young age, often without having been ridden.

- Trauma. The structures in the leg are often prone to injury. Any accidents in the field/stable etc. could cause damage the vagina fibrosa or the tendons / ligaments it is closely connected to.

- Training. Certain ways of training could lead to imbalances / too much pressure on the tendon structures within the leg. Hypermobile movement can be recognized by dropped fetlocks, extreme extension of the hindlegs (without proper flexion) and often a hollow back and other signs of disbalances.

So how could we treat issues with the vagina fibrosa? This is where it gets tricky, because there is so little information about it. Few options are available:

- Change your training. It is possible to learn horses move more upright and to balance the weight on the legs properly. Even when they have congenital hypermobility, it is possible to ‘reset’ the muscle memory. An important tool for this is GROUNDWORK where we can strengthen our horses without putting the extra (and often we are also unbalanced) weight on their backs.

Look at this collage picture. Picture one is a horse with dropped fetlocks, hollow back, extreme extension of the hindlegs, restriced whithers / shouders. On picture 2, the horse is FAR more upright, balanced and lifting. This horse was MAINLY trained in groundwork and after a few months I went on her back and this was the result. However, it is still very hard for the horse and he head is on the vertical, with a slight bend at the 2nd / 3rd cervical vertebrae. On the picture below, you'll see how the horse canter's now in a natural way. It's easy now. She's able to keep the poll the highest point. Picture 2&3 both show great improvement, but for this specific horse I like picture 3 the best.

- Bloodtests can reveal inflammations in the body. It doesn’t locate, but it could help as a starting point to start searching and there are medications available to alleviate.

- It is possible to ultrasound. However, your veterinarian must 1) know about it and 2) know how to ultrasound it as it a very tricky task and as its very little and there are many surrounding structures. Many veterinarians are not aware of the vagina fibrosa and they’re not to blame. It’s not the textbooks. You can not do what you don’t know and you can’t know what you haven’t learned. And yet the more we learn (about horses), the less we actually know.

Every dissection, I discover / see something I have never seen before. And even in my daily practice I still experience so many ‘first times’. Not knowing everything is not a weakness. We simply can’t and it would take away our desire to learn, the feeling of being amazed by nature and it would stop us from looking at things in different perspectives. We all can contribute a piece to the puzzle if we stay openminded. In fact, it is my personal belief we OWE this to our horses as they are more openminded to us than we could ever be to them. And that’s why I keep on learning. Every. Single. Day. Will you join me?


A special thanks goes to Zefanja Vermeulen from Equinestudies for educating me. Thank you for bringing Sharon May-Davis to The Netherlands and allowing me to learn!

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