Sunday, March 01, 2015

Horseshoe Biomechanics by Dr. Jenny Hagen for Werkman: Side-Wedge Shoe for Medial-Lateral Imbalance

Click on the triangular "play" icon (bottom left) to start Dr. Hagen's video.

The Hoof Blog is pleased to share with you the next video from the research of Dr. Jenny Hagen at the University of Leipzig in Germany. Today we share the biomechanics of the "side wedge" shoe, used to correct medial-lateral hoof imbalance, especially as identified and measured in radiographs. Dr. Hagen's video 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, wide toe, wide-branch (asymmetric), and open toe shoes) posted in October and January.

Dr. Hagen's latest video is technically on one shoe but it touches on some very key principles in equine hoof balance and conformation "correction" via therapeutic shoeing. Most importantly, it examines whether farriers should be shoeing for landing or loading, and whether correction of joint space to create a more aesthetically pleasing radiograph is worth gambling on the stress placed on collateral ligaments when wedging the foot.

Viewers may find it helpful to watch the earlier videos, especially the egg bar and heart bar, before watching this video, in order to become familiar with the protocol that Dr. Hagen uses to evaluate the shoes. She uses a special type of radiography block to simulate the difference between a horse standing on soft vs hard ground, for instance.

A critical question for this video is what the difference would be if a farrier applied an actual side-wedge shoe--in which the branches of the shoe are two measurably different thicknesses--or a flat shoe with a plastic or leather wedge pad added to one branch of a flat shoe and not the other, as was done in this video.

Dr. Hagen does acknowledge in the narrator's script that an actual side-wedge shoe would add weight to the wedged side of the foot as well as elevation, but she does not speculate on what the effect of that weight would be.

It might be slightly confusing that a plastic wedge pad and a steel horseshoe have different densities in a radiograph. If you watch the video on your phone, you might not "see" the wedge pad in the radiographs, but the narrator does a good job of explaining it.

The two primary reasons to use a side-wedge would be to modify the landing pattern of a hoof or to adjust coffin joint space based on a radiographic approach to correcting medial-lateral hoof balance or conformational abnormality. As with the previous videos on specific shoes, Dr. Hagen points out that the immediate positive attributes of attempting such a mechanical adjustment for the purposes of radiographic improvement of balance require some compensatory changes elsewhere in the hoof capsule or higher up in the limb, so there are always trade-offs when deciding to use a shoe with mechanical intent.

Of all the videos in the series, this one seems to be the clearest to show the effects of the shoe on the foot. Dr. Hagen also touches lightly on questions that keep farriers up late at night: landing vs loading, for one; and the instant gratification of wedge pad use weighed against the device's cumulative effect on the hoof capsule, not just the structure that needs a lift, for another.

And finally, what happens to that uneven joint space seen as problematic on a radiograph taken when the horse is standing on a hard surface, once he is ridden in arena footing, stands in his soft-bedded stall...or enters a turn on any surface? And if the horse was taken off the block and no therapy applied, would the joint space disparity necessarily be the same the next time he was radiographed, or if he was radiographed by a different technician or under different radiographic protocol?
Of all the videos in the series, this one seems to be very straightforward in its explanation, once you are clear which side of the foot is the wedged side in all the images.

Dr. Hagen's advice on this method of shoeing is to proceed with caution. "Temporary and limited application is recommended," the narrator tells us. While the method may be desirable for alignment adjustment, the wedging will have an effect on the entire hoof capsule, the horn architecture and the circulation within the hoof. An increase in tension on hoof horn can lead to cracks.

About Dr. Hagen:
Dr. Jenny Hagen supervises the research group “Equine Locomotor System and Hoof Orthopaedics” at Leipzig University's Institute of Veterinary Anatomy. The group includes four PhD students, at least one farrier and Dr. Hagen. Their study of orthopedic horseshoe modifications included the comparison of 10 horseshoe modifications and four standard horseshoes and was carried out using 25 horses. She was also consultant to the creation of the hoof anatomy app, Hoof Explorer.

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