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Wednesday, April 25, 2012

ON THE (Ringbone) CASE: One-Piece California-Style Lateral Breakover Base Keeps a Horse on the Move--in All Directions

Dateline: Southern California
with Farrier Ernest Woodward and Veterinarian Mark Silverman

Before the trail of their “in the field” California-style version of Fuego’s Euro 3-D lateral rocker shoe  went cold, Woodward and Silverman turned their attention to what else they might have at their disposal to use as a platform (literally) for this concept.

The challenge this time: create another version of a lateral rocker shoe that does not incorporate a traditional "shoe" for the base and the nailing surface--but have it be made in one piece instead of three.

The case: an aged warmblood with ringbone affecting P1 and P2.

Woodward and Silverman had accomplished this in the previous case (see link) by using an aluminum plate screwed to a smaller pony shoe, along with a liberal dollop of sole impression material.

Our case: a pleasure horse with pastern ringbone pathology of P1 and P2, as illustrated in this detail from an oblique-view radiograph. The bony irritation was causing visible soft-tissue swelling (see bulge at right) in the pastern area. A horse like this would be limited to work on a forgiving surface, but even in soft footing would not have much lateral flexibility. A sympathetic shoeing system might help the horse be happier in its work.
What would they engineer this time? The first photo they sent was just a blue rectangle. After a bit of squinting, it became recognizable as a Sigafoos Series II plate. And they were going to nail right through it. No glue.

I imagined Rob Sigafoos rolling his eyes. But the wizard of hoof adhesives might take pleasure in the fact that someone was thinking outside the rectangle of his plate.

They would transform it from a stabilizing support base used for seriously lame horses into a motion-conducive pivot base for a horse that needed some added mobility. Stability was sacrificed for mobility for this application.

First, the base material. The Sigafoos II plate is a sandwich of
high-performance polyurethane around a central plate of aluminum.
Woodward: “The main reason for setting this objective was to shorten the distance that the shoe adds to the length of the hoof along the outer circumference of the hoof capsule.

"Think of it this way: what if we could use a 4 mm (thick) plate and grind it down to 2mm at the edge? We could bevel it to its full thickness inside the nailing surface, as opposed to the standard 8 to 10 mm thickness of a ground-surface breakover shoe with another foot surface shoe/plate then welded or attached to it.
The plates are available both flat and wedged. The one that used for this horse was wedged--note gradation of the foot surface (bottom) from left to right (ground surface at top). The aluminum plate is a uniform thickness.

“The layer cake effect was good for breakover (on the previous test case) but it added length to the whole foot and migrates the bearing surface of the hoof wall further and further away from the center of rotation of the coffin joint.

“The big benefit of the shoe-free concept is that it gives the hoof a motion similar to a round motorcycle tire vs a square car tire. As the motorcycle leans over, a square tire is forced to go up on its edge.

This view illustrates the heel of the appliance; it is raised off the ground by the polyurethane ground surface. Note how the wall bearing surface has been rockered to half its thickness. The horse's prolapsed frog will sit comfortably on the pad.

"Considering the anatomy of the distal limb, this edge-effect causes the joints to take load unevenly and puts lateral "bend" in the distal joint structures.”

Dr Silverman: “It's an important concept to understand that the distal structures of the limb are designed to accommodate terrain irregularities and angular deflections associated with turning. The mid and upper portions of the limb can only handle flexion and extension until you get up to the most proximal joints.

The ground surface is cushioned by the blue polyurethane which was
ground off the aluminum plate at the wall bearing surface. The polyurethane has been drilled to allow penetration of the dental impression material that will cushion the sole and for weight reduction.
“This is all fine in a physiological system, but once you involve a pathologic change, trouble comes. This is why with something like ringbone we need to help the horse accommodate the normal challenges of turning and uneven terrain.”

Returning to the motorcycle analogy, how much easier on the horse’s joints would a round edge be than an abrupt, square edge?

Woodward: “This turned out to be a very clean shoe design that had more concussion absorption and traction built into it than the layered plate-and-pony-shoe version had. That said, it required a bit more sculpting...“

The lateral view clearly illustrates the breakover point and the wedge effect.
He continued, "We have a lot of these plates at the clinic as Dr. Silverman is, as far as I know, one of the few people in southern California who has ever applied the very labor-intensive finished product. So he thought it would be a good starting place to build a shoe that offered the kind of movement he wanted for this case.

Woodward: "The urethane tread provides not only traction but also a significant dampening effect. Also, the layer used to adhere the cuff to the plate provided a nice separation as a built-in polyurethane pad. This is also nice because it keeps the hoof from direct contact with the aluminum. You can run into corrosion issues between aluminum and the foot."

The heel view gives the impression that this is a shoe sandwiched
between two polyurethane pads...but it's all one piece.
Woodward: "To our knowledge no one has modified this plate for this use. This is not to say no one ever has, just we have never seen or read about it if they did."

The same design was used for both front feet. “the mechanics needed to be similar or I think that we may have had trouble with overall stability and balance,” Silverman commented.

How did it work out?

The finished one-piece package nailed onto the foot (left fore). Notice the prominent soft tissue swelling (arrow) from the ringbone.
Dr Silverman: “The patient is definitely more comfortable in the shoes, though there was a bit more soft tissue inflammation around the bony changes. We've been going after that with therapeutic ultrasound, coupled with triamcinalone ointment.

“Surgery was not an option for this horse. He's 26 years young and the owner didn't feel that it was a good idea to put him through it, though with a joint like this I would have at least consulted a surgeon to discuss surgical fusion of the pastern joint.

Lateral view of the left fore after shoeing. The pastern swelling is less obvious from this angle. The same device was applied to both front feet.
“Surgery is probably not practical at this horse's age and he actually is getting around ok as a limited trail horse for now.

“This experimentation--and seeing its effect on the horses--has led us more and more to really look hard at the motions and movements of our “normally” shod horses and how those horses interact with different footings and surfaces. This has been a very eye-opening line of development for our everyday horses.”


On the Case: The Woodward-Silverman California-Style Euro Rock 'n Roll Shoe

Dressage, Fuego-Style: It's What's Underneath That Counts as Euro Rocker Shoes Score for Spain (by Fran Jurga with Hans Castelijns, Erin Ryder, and many others)
On the Case with Austin Edens: Engineering Prevention of Support Limb Laminitis with a Removable Clog Screwed to a Shoe

Motorcycle race image courtesy of Flickr user Phil Parsons.

Begins 25 April...runs til the back room is empty!

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