Friday, January 16, 2015

Biomechanics of Horseshoes by Dr. Jenny Hagen: Werkman presents the wide-branch (asymmetric) and open toe shoes

collateral ligament injury therapy shoe
In this still image from Dr. Hagen's video, you see the wide branch shoe used in the biomechanical testing (top left) and the results of the pressure mat testing (bottom left). Top right shows the gross anatomy of the horse's foot with the ungual cartilages exposed.
The Hoof Blog is pleased to share with you some additional media from the research of Dr. Jenny Hagen at the University of Leipzig in Germany. Today we share the biomechanics of the "wide-branch" (asymmetric) shoe, and the "open toe" shoe. Dr. Hagen's research is sponsored by Werkman Horseshoes of The Netherlands.

This video picks up from the previous videos from Dr. Hagen and Werkman (biomechanics of egg bar, heart bar and wide toe shoes) posted in October.

The late American film critic Roger Ebert would definitely give this video his famous "thumbs up" rating. The British narrator is reading the script in a rather matter-of-fact tone of voice, without much inflection but at about the five minute mark in the video, listen closely: she remarks that the shoe's effects on the coffin joint space is contrary to what one would expect.

But is that what you were expecting?

So pay attention, you will be asked to think here. Think ahead, and see if you are right or wrong. And does the shod foot exacerbate the joint capsule space seen in the unshod foot...or not?

I had to stop and start and go back on this video many times, both to understand the matter-of-fact narrator and to fully observe the images. But that also probably means that I got more out of this than if I had cruised through it once, nodding my head.

Keep an eye on the guides in the slides that are marking the medial side of the foot for you, and make note of which side of the foot has the narrow branch and which side has the wide branch. You are not looking at a pair of feet. The medial side is on the left on all the feet.

It might be helpful to think of the shoes as "wide lateral" or "wide medial".

Dr. Hagen warns that the wide branch shoe should be used with the owner's understanding and provision of the suitable surface for the horse to be standing on and working on. The shoe is for temporary use only.

She stresses that these shoes are applied because of a soft tissue (tendon or ligament) or bone injury in the foot, and that the well-being of the hoof capsule takes a back seat as long as the shoe is on the foot and changing the pressure distribution.

However, these changes, even when temporary, may affect the blood flow to and within the foot and disrupt the architecture of hoof horn, even to the point of promoting horn cracks, Dr. Hagen asserts. Another plainly stated criticism is that by changing the joint space in the coffin joint, strain is put on the collateral ligaments of the coffin joint.

In summary, she states, "On the whole, all the anatomic structures forming the distal extremity form a close regional and functional relationship. Therefore, the unilateral narrowing of the joint space will inevitably cause an additional load for his joint surface and distinct stretching of the collateral ligaments on the other side. It is safe to assume that relief for one structure causes additional strain on the counterpart so that the efficacy and the temporary limitation of the shoe modification should be carefully considered for each individual case."

In this shoe's defense, I think that a lot of different shoe designs are lumped under the name "wide branch", "asymmetric", or even "narrow branch" shoes. It makes sense that no two would be alike, since they should be custom-made for the horse's foot and for the injury, but the variation is huge. I have also heard lateral extension shoes--where the wide part of the shoe extends out from the hoof perimeter--under this heading. Surely it would behave differently than Dr Hagen's super-wide shoe.

In fact, it would be interesting to test the width of the branch's effect on the joint capsure space by manipulating the shoe's design.

I also remember from Professor Denoix's lectures and writing on this shoe that he is adamant about the management of the horse while it is wearing this shoe. It is not for an acutely injured horse and the horse must not be circled; it should be walked in straight lines and should live and be exercised on a soft, uniform surface at all times.

Dr. Hagen has pointed out what can go wrong if the protocol isn't followed.

The next shoe is one that is seen more in Europe than in the United States, but is starting to be more popular here. The open toe shoe, or as some people like to call it, "the open-toe egg bar". It was once called simple a "reverse" shoe or even a "backwards" shoe, but that was much too simple.

If you watched the videos posted here from October, you know that Dr. Hagen has been meticulous in testing and describing each shoe in parallel terms.

Dr. Jenny Hagen of the
University of Leipzig
Veterinary Anatomy
This shoe, however, was another one with an aha! moment that reminds us how important it is to be aware of the surface that a horse will be standing on--and to try to manage a horse with laminitis so that it is standing on the optimum surface for its shoe--or wearing the optimum shoe for the surface, if there are fewer choices on the management end. It seems obvious like this would be the most forgiving to the fragile toe area of the foot, but that might not be the case.

I hope that this series of videos will have an effect on people who believe that there is a specific shoe for a specific injury or conformation problem. Dr. Hagen states so beautifully that the choice of a shoe--or even whether to use a shoe--should be based both on how it serves or compromises both the hoof capsule and its inner structures but there is also to be considered how the shoe affects the alignment of the lower limb, which she says is in turn influenced by what the horse's toe conformation and whole limb conformation can offer, and what the ground conditions may be.

How do you put all that together and decide on a solution that will stay on a horse's foot for a month or more? With all the imaging and evaluation tools we have today, it seems like we should be checking hooves much more often, especially on horses with laminitis, and making many more adjustments and changes than we have in the past.

Research like this also brings into focus how high the risk is to leave therapeutic shoes on for too long. It's not enough to put a date on the calendar to put shoes on a horse's feet. There has to be a second date marked: the day to take them off.

Unfortunately, Dr. Hagen's high-speed fluoroscopy video is not coded for US websites so it can't be displayed. Hopefully that one can be shared at some point in the future. She has more shoes in this series. 

Dr. Jenny Hagen will be a speaker at the 2015 Werkman Spring Games in The Netherlands, to be held April 16-18, 2015.

To learn more: 

"The Collateral Ligaments of the Distal Interphalangeal Joint: Anatomy, Roles and Lesions" by J-M Denoix, DVM, PhD in Hoofcare and Lameness: Journal of Equine Foot Science 70 (1998)

"Corrective Shoeing of Equine Foot Injuries" by J.-M. Denoix, H. Chateau, and
N. Crevier-Denoix in Proceedings of the 10th Geneva Congress of Equine Medicine and Surgery, 2007.

"The biomechanics of the equine foot as it pertains to farriery" by Ehud Eliashar in Veterinary Clinics of North America: Equine Practice 28 (2012) 283-91. 

"An evidence-based assessment of the biomechanical effects of the common shoeing and farriery techniquesby Ehud Eliashar in Veterinary Clinics of North America: Equine Practice 23 (2007) 425–442

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