Reverse Wedge Shoeing for Founder
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Mark Andrews is an equine vet in a large mixed practice. In addition to a veterinary degree, Mark also holds the Certificate in Equine Practice.
After qualifying at Edinburgh, Mark worked in mixed practice in Lincolnshire and Hertfordshire, before returning to Lincolnshire where he is now based. Mark's daily workload is varied; there is a lot of stud work which is seasonal, lameness cases take up much of the remaining time, along with respiratory disease and general medical cases. Marks also spends some days on duty at the three local racecourses.
In his spare time Mark writes articles for the Equine Science Update newsletter and website.
"The benefits of reverse wedge shoeing for foundered horses were described at a meeting of farriers and veterinarians. According to veterinarian Eric Belloy, and farrier Gary Martin, the procedure can make foundered horses pain-free more quickly than other methods, whilst giving them the support they need.
A foundered horse bears weight on the tip of the pedal bone (P3) - putting pressure on the sole, causing pain and restricting the blood supply to the solar corium and P3. This leads to reduced sole horn growth.
The goals of treatment include reducing pain, protecting the foot, and avoiding further movement of the pedal bone. The aim is to restore normal function as far as possible. “But you have to be realistic“, Belloy points out. “The horse may not return to its previous level of work.”
Reverse wedge shoeing aims to realign the hoof capsule to the pedal bone. The heels are trimmed to a more natural position in relation to the lower border of the pedal bone. The shoe is attached to the foot with glue rather than nails. Because of the way the foot is trimmed, there is a gap between the shoe and the foot at the toe. This gap is filled with a temporary wedge to maintain the position of the shoe as the acrylic sets.
Belloy emphasises the importance of frog support “I believe it is vital to support the frog. Frog support relieves the pressure on the tip of P3, and spreads weight bearing to the non-painful areas. It may reduce or prevent further change in the position of P3 - although it is unlikely to push the pedal bone back into a normal position.”
“I find it difficult to decide how much pressure to use with a metal shoe” he continued. “But using a reverse wedge shoe with silastic frog support is more physiological than a metal heart bar shoe. It moves as the foot grows. My impression is that it maybe works better for sinkers”.
If the horse is not more comfortable once treated , and there is tension in the DDFT, raising the heels may help.
The ability to realign the pedal bone may be limited if traditional methods are used. There may not be enough hoof - as a result of underrun heels, or after paring abscesses - to allow adequate trimming. Some feet may be too painful to allow the shoe to be nailed on.
So what are the benefits of reverse wedge shoeing? Trimming the heels strengthens the horn and allows the frog support to be more effective. The break over point is moved back compared with traditional methods, and so there is a decrease moment arm on the dorsal wall. The horse does not bear weight around the tip of the pedal bone. As the horse is not bearing weight on the wall at the toe, it grows down more quickly.
“With our technique we can trim the hoof back, then build up the hoof. It relieves pressure on P3 and spreads weight-bearing” said Belloy.
“We started doing this (procedure) as preparation for tenotomy as described by O`Grady. But we found that many of the cases got better without the operation.”
Farrier Gary Martin went on to describe the practicalities of applying the reverse wedge shoe.
The first step is to assess the radiographs of the foot and estimate how much to trim the heel, how far forward the trimming should extend, the thickness of wedge required between the shoe and the foot at the toe, and where to place the shoe. As well as the latero-medial view, centred on the bearing surface, he recommends a dorso-palmar view in all but the most straightforward cases to assess medio-lateral balance and sideways rotation.
Then trim the bearing surface to realign it with the distal border of P3. “Make sure to remove all dirt in the white line and all poor horn.”
Select and prepare the shoe. “Aluminium is easiest. Adjust the fit if necessary. Grind the foot surface to provide a better bond. Fit the shoe to provide plenty of heel support.”
Prepare the foot. Use sand paper to clean the wall and bars in the area where the resin will be applied.
Select the frog support. He uses dental impression material or silastic frog support held in place by fibre glass mesh “Avoid pressure on the sole around the tip of P3, and over any areas that show pain with hoof testers.” He feels that this type of frog support is better than a heart bar “You can always cut away any excess if you have increased the pressure too much.”
With this method there is no need for a dorsal wall resection (DWR) .“We have not carried out a DWR for 12 years. Leaving the dorsal wall in place provides strength to the hoof capsule.”
Apply the shoes and wrap with cling film. “In the winter it will take up to 8 minutes to set.”
The final stage is to rasp up, and check comfort. Raise the heels using trailers or rails if necessary.
What to do afterwards? They suggest box rest for at least 3 weeks, followed by a gradual increase in walking in hand. The shoes should be replaced every 4-6 weeks. They recommend gluing on until the soreness in front of the frog has gone, and the wall has grown enough that a wedge is no longer needed. If trailers were used to raise the heels they should be reduced a little at each shoeing.
“The biggest problem we have had is removing the shoe. We remove the frog support, then saw with a blade and finally use snips to remove the shoe”
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