Unstable hooves, dysfunctional feet

An ex-racehorse was in need of some serious farriery attention when presented to Andrew Poynton with cracked, overgrown, unstable hooves. Here, he explains how synthetic materials, adhesives and plastics can be a real game changer in the treatment of such cases.

Materials and equipment required

• Imprint Hoof Repair (lowtemperature thermoplastic @65 shore D)
• Imprint Ultrafast Adhesive (fast-curing, moisture-tolerant methyl methacrylate)
• Imprint Sport Shoes (composite, synthetic, shockabsorbing, mould-on shoes)
• Imprint Shoe Freezer (refrigerant aerosol)
• Surgical spirit
• Keratex Hoof Putty (medicated wax)
• Modified 10 mm twist drill bit
• Cordless drill
• Regular farrier’s tools (rasp, nippers and knives)
• Small butane torch

Case description

This case, an eight year old thoroughbred gelding, recently retired from racing, was referred with his feet in very poor condition. His hooves were long overdue for attention and he walked lame on the right fore (RF). The RF was in the worst condition, having an almost complete, complicated central toe crack and a full-depth complete lateral quarter crack (Fig 1a). There was a lump of aluminium and adhesive perched on the middle of the toe (Fig 1b) supposedly to hold the toe together but in fact achieving nothing positive.

The left hind was next in terms of severity, having a complete lateral quarter crack with the associated hoof flare and distortion. The right hind was overgrown, with superficial lateral toe cracks and a low central toe defect that had been excavated to a height of approximately 12 mm. The left fore was the only hoof without a crack but, like the other feet, was long, with flaring and irregular growth rings.

Although the horse had been shod with heart bar shoes in front, the neglected state of the feet meant their value was limited.

By looking closely at the coronary band of the RF, it could be seen that instead of a flowing arc from heel to heel, the arc was irregular, with acute points where the hoof cracks radiated from (Fig 1). The line of the coronary border also deflected vertically at these points. In effect the deformed, cracked and
dysfunctional hoof was damaging what it was derived from, the coronary corium.

External issues, internal impact

The ripples or corrugation visible externally reflect internally, creating unwanted compression and tension of the lamellae, sandwiched between the hoof wall and the third phalanx (P3). Instead of working as an integrated unit, absorbing and dissipating impact and then recoiling to utilise the energy for propulsion, the foot was experiencing focal forces at the stress points where the cracks appeared, causing trauma not only to the hoof capsule but internally to the soft tissue and vascular structures. The loss of integrity of the hoof capsule will ultimately lead to tearing of the laminae, causing bleeding and bruising.

The loss of hoof wall integrity had the knock-on effect of overloading the sole, causing it to flatten and spread, leaving little or no room for suspension; solar bruising was the inevitable outcome.

The aim of treatment

The horse needed treating to reverse the trend towards irreparable damage. Trimming to remove all deviated and undermined overgrowth allows the foot to begin to equalise the stresses it is subject to. With seriously compromised cases like this one, it is unlikely to be possible to trim out all the deformation in one session without further weakening the hoof capsule. That said, as this case reveals, much headway can be achieved towards restoring a functional foot. Synthetic materials, adhesives and plastics such as those used in the treatment of this horse have become a real game changer. Building a prosthetic, synthetic hoof capsule can begin to restore normal healthy foot function and a vast amount of progress can be achieved in a single session.

Approach to treatment

All four feet were treated in the same manner, but, to avoid repetition, this article focuses on the approach to the RF as it was showing up much more lame than the others.

On the first two occasions that the horse was treated, he was sedated so that the treatment could be carried out safely. As with most cases of this type, the feet were treated one at a time, working on the most painful first, in the hope that when the procedure is completed on that foot, the patient will stand more comfortably, making progress easier as the other feet are worked on. All cutting was carried out using rasp nippers and a selection of knives, including a favourite searcher, which do not produce dust or high-pitched irritating noises and leave the excavation site clearer to see, with less debris present.

The trim

Lateromedial and dorsopalmar radiographs had recently been taken of the front feet (Fig 2), which were helpful in locating the exact position of P3, thereby allowing for a keen trimming. As the method of shoeing did not require nailing, it was possible to trim to remove the flaring of the hoof wall, something that otherwise would not have been safely feasible.

The sole, frog and bars were attended to first, with careful cleaning using a knife. Any deformity of the bars that could be removed was pared out. Moving onto the hoof wall, as much flaring was removed as possible, attempting to regain a straight wall from coronary border to distal edge, trimming as far as the white line so a sole view revealed just that – sole and little wall.

Attention then turned to the hoof lesions. The lateral quarter crack extended to the coronary border and was full wall depth, but was not currently bleeding (Fig 1a). The toe crack extended to within 12 mm of the coronet, was full depth and undermined the wall more at its lower half, extending to the soft tissue of the lamellae (Fig 1b). A capillary vessel was snagged while debriding this area, so it was cleansed with surgical spirit. Where the defect was deeper than the hoof wall, some Keratex Hoof Putty was used to fill it and cover the spot that had bled (Fig 3a). This meant the Imprint Hoof Repair material would then not create an inward corrugation but rather something more akin to a healthy hoof wall.

Applying the shoes

Using a 10 mm diameter modified wood drill bit (with the centre reduced to 1 mm) fitted with a depth gauge/stop, multiple keying points 3 mm deep were made either side of the lesions in preparation for forming a strong ‘dowelling’ union between the hoof wall and the prosthetic rebuilding (Fig 3).

Next, a thin layer of adhesive was dispensed over the areas to be filled and then some ready-softened Imprint Hoof Repair was modelled onto the hoof, making sure both the drilled areas and the voids in the hoof were filled with the material.
An access window in the repair was made over the snag site so that it could be opened up in the event of infection (Fig 4a). In this case, it was not needed.
Care was taken to not extend or enlarge the repaired hoof with the material (Fig 4b). The objective was to mimic hoof capsule function, and making the repair material too thick would cause constriction. The horse was allowed to stand weight bearing while the material cooled and hardened (making the process less stressful for both patient and farrier!). A little refrigerant was used in the centre of the plastic where the mass was greatest so that it would harden relatively quickly (5 minutes).

As the sole was flat and painful, a thin layer of adhesive was applied (Fig 5a), followed by a thin layer (about 2 mm thick) of the Imprint Hoof Repair material, which was modelled to create a healthier sole shape with a little concavity and an outline following the hoof wall to slightly elevate it. The outer margin wrapped onto the lower hoof wall by a couple of centimetres, and this provided a thicker, bonded sole that would still be able to move (the bonding avoids condensation and softening of the sole). The inner margin extended as far as the frog (Fig 5b, 5c).

An Imprint Sport shoe was then fitted. The lower border of the now plastic hoof was slightly heated using a small gas torch to make the plastic sticky and the preheated Imprint shoe was fitted by plastic welding the two together (Fig 6). This created an extremely strong and durable union with the hoof. The shoe has a broad frog plate, which covers and maximises the bearing surface in the palmar region of the foot. Importantly, the frog plate part of the Imprint shoe is not bonded to the frog; access is still possible so it can be cleaned via the central cleft and alongside the bars. When all was hardened, some finishing with the file side of a rasp completed the procedure.

The result was immediate, with the horse standing full weight bearing on the RF (Fig 7). The other three feet were treated similarly although they did not needing the sole casting.

Subsequent shoeings

Further regeneration of the feet was achieved at subsequent shoeing sessions every six weeks. At the second visit six weeks after initial treatment, no further hoof repair was required as all bonding was sound in and around the defects (Fig 8a). The sole casting on the RF was no longer necessary (Fig 8b). All feet were shod as at the first visit. At this time, the horse was 1–2/10 lame on the RF.

At the third visit 12 weeks from initial treatment, the horse was moving soundly. As well as reshoeing in the same manner, the lower portion of the RF toe defect was removed and refilled it as it was starting to come away a little where the hoof putty was placed. The other defects were holding well and growing out. At the proximal border of these defects, the wall was excavated, cleaned and keyed higher up, extending the defect repair to its extremity as the horn had grown down intact away from the coronary border.

Conclusion

At the time of writing the horse is sound and in work. It is anticipated that the approach described will be continued for the foreseeable future until the feet can safely be shod with conventional steel and nails. The client is pleased with the transformation of her horse’s feet.

Apart from the materials used to remedy the situation, the hoof trimming played a major part in the recovery of this patient. It is also worth noting that the soles were not packed out with any form of fillers, thereby allowing the foot to move naturally while maintaining traction. The most important requirements are attention to detail and patience.

This relatively simple method of treatment should give hope to farriers and horse owners alike, as with quite extreme cases, such as this one, much can be achieved in a relatively short space of time to restore the horse to soundness.

From a case report which first appeared in the Forge Magazine supplement, Forge Knowledge, May 2022. © Andrew Poynton FWCF