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Frog Pressure - Modern Applications

Updated: Nov 2, 2019

Frog function is a vitally important factor in hoof health, a cliché has emerged amongst some farriery circles “use it or lose it.” In the context of the frogs relationship with the digital cushion, as the digital cushion has a poor blood supply and therefore limited regeneration properties. When we shoe the horse we reduce the functionality of the frog as we lift it further from the ground, studies have shown that both the expansion and contraction of the hoof is reduced with the application of a shoe compared to the barefoot (Roepstorff 2001), often heart bar shoes are used to utilise the frog in the treatment of hoof pathology and weak dysfunctional hooves.

The heart bar shoe has been used historically as a remedial shoe for many pathologies, laminitis being one, Eustace and Caldwell (1989) expressed its efficacy in the treatment of solar prolapse as a result of laminitis and many studies before and since have advocated its use in treating the pathology. Brown (2015) outlined the mechanisms for its use, stabilisation and load sharing, explaining that applying “positive pressure” to the frog de-loads the laminal bed where damage is occurring. O’Grady and Parks (2008) also expressed the same use but stated that it was unknown if the heart bar provided any further benefits, in the same paper it explained how this focal pressure can cause adverse effects and utilising a larger surface area can be more beneficial. In recent years there has been research into other effective farriery treatments such as the clog which Reynolds (2018) found to produced the least amount of surface tension of the hoof when compared to the heart bar and other techniques including the use of modern materials to provide this vital frog support. See my article on Laminitis for further reading.

https://www.theequinedocumentalist.com/post/laminitis-pictures-and-x-rays-speak-a-thousand-words

Other uses for the heart bar has been flat/weak heeled feet and cracks, again in an effort to utilise frog support to unload the compromised structures, Jim Blurton advertises the shoe as mimicking the unshod foot restoring the natural pattern of weight bearing and supporting the coffin bone, yet Podol (2006) stated that incorrectly applied the heart bar can become a “Damaging piece of equipment” and Castelijns (2002) listed other disadvantages including their lack of efficiency in deeper frogs and their tendency to induce frog atrophy.

It can clearly be seen that the foremost reasoning behind the application of the heart bar is (re-) utilisation of the frog after application of a rim shoe that lifts it off the ground, but the frog is deformable and soft, while the heart bar is rigid and hard. Let’s take a min to outline the functions of the frog. Young (2018) outlined these important functions, the dissipation of forces from locomotion, weight transference of the bone column and blood circulation, it also discussed how these functions are made possible by its makeup and harmonious relationship with the other hoof structures.

Diagram showing how the frog transfers and dissipates the ground reaction force by its relationship with the other internal structures, this displacement of these structures is also the mechanism of blood circulation. The frog provides support and cushioning for the descending body weight.

What’s important to appreciate is that once the foot is unloaded so too is the frog and everything returns to its unloaded position, this is also part of the hoofs blood circulation mechanism.

Now lets consider the heart bar, as stated by Young (2018) it is a fixed metal plate which can be fitted with positive or negative pressure to either provide constant support or loaded support respectively, however it can not provide any further advantages or enhancements as agreed by O’Grady and Parks (2008) and can actually either be useless or harmful depending on the fit, which is also influenced by hoof growth as the heart bar only sits where its intended until the hoof growth moves it. In the case of positive pressure the internal structures do not get any relief or return to origin, this must in the authors opinion influence the pumping mechanism and also the expansion and contraction mechanism as suggested by Watson (2016).

So the question is what can provide the benefits of the heart bar while more accurately mimicking the unshod foot and add other advantages? Young (2018) perhaps points us in the right direction although it was only a pilot study, it used pressure plates to assess the comfort of horses with caudal hoof packing versus a heart bar and found that the horse was happier to bear more weight on the hoof packing than the heart bar. Casserly (2018) also expressed improvement in palmer angle and sole depth in horses with frog support padding over and above the use of heart bars.

One of the added benefits of padding over a heart bar is the increased surface area, allowing load sharing not of only the frog but of all the solar structures, more closely mimicking the bare foot. The yellow line back to the heels expresses Young (2018) area of caudal hoof packing where the red area in this image shows the surface area of a complete solar application used by the author, the packing also ensures perfectly even contact throughout the entire shoeing cycle.

Pictures showing the authors use of 3rd Millennium (

https://www.facebook.com/the3rdmillennium/

) frog support pads and P3 pour in padding and EDSS impact material in cases that would historically have been candidates for heart bars.

Casserly (2018) used frog support pads as in these images but with a different packing method, this method also utilises a much larger surface area, the heart bar shoe is of course also a bar shoe so if this extra stabilisation is required the added benefits of a deformable frog contact and increased surface area can still be applied with a frog support pad fitted under the bar shoe, the authors experiences of this method are similar to Casserly (2018) and uses this method extensively to provide support to weak heeled feet. These findings have also been echoed in a recent study presented by Haydn Price at the BEVA congress 2019, on his studies at the RVC outlined the positive impact packing can have on the internal structures of the hoof, essentially creating immediate frog support on impact which “locked” the internal structures of the hoof and enhanced hoof function.

Although not compared to a heart bar, Roepstorff (2001) showed that adding hoof padding restored the hoof function closer to that of the bare foot, so this can go some way to explaining the success of applying hoof padding to weak feet as experienced by both the author and Casserly (2018), further study could be done incorporating the heart bar in to these statistics to determine it efficacy in comparison, but with the findings of Young (2018) the author would hypothesise that the heart bar would, specifically fitted with positive pressure, have a reduced expansion and contraction.

Another further technology that could be utilised in place of the heart bar is Formahoof, although studies like Young (2018) and Roepstorff (2001) would need to be done to assess its effects on the parameters we have discussed, its deformability and utilisation of all the hoof structures while mimicking the solar surface would suggest it would have similar benefits to pour in padding.

Formahoof (

https://formahoof.com/

) creates a protective layer without nails, closely mimicking the bare foot.

Formahoof also has proven effective in the treatment of laminitis and was actually invented with this pathology in mind, it allows you to instantly rebuild and stabilize the hoof structure, providing immediate relief, allows the hoof to remain in a medicated environment during its healing process, prevents re-infection by stopping urine, faeces and debris from reaching the infected area while keeping the healing environment clean. It supports the hoof capsule through the natural regeneration process and it restores the hoof capsule and sole arch, giving instant relief to horses that have severe rotation and P3 penetration.

Example of Formahoof used in laminitic case.

Formahoof.com

Another consideration for the added advantages of an increased surface area provided by packing is its ability to help keep the hoof on top of the surface of sand schools and other softer goings, many studies have attributed the onset of pathologies such as navicular and collateral ligament desmopathy to the repeated backward or sideways rotation of the hoof on soft surfaces and hoof packing could go some way in negating this. Considering the close relationship between navicular and weak low heels, a symptom often treated with heart bars, this could add to the extra benefits of padding over and above the heart bar.

There is perhaps a half way house, if the heart bar is fitted with a gap between the bar and the frog it can then be filled with impression material of pour in padding, it is unclear how the heart bar was fitted in Young (2018) but an interesting study would be to compare different fittings with different materials.

So with the advances in technology and the findings of recent studies has farriery transcended the heart bar? With modern advances the advantages of the heart bar can be appreciated without the possible negative implications and difficulty in fitting and with increased advantages, so is there a time when a heart bar would be more beneficial? Perhaps it all depends on what the intended outcome is.

Taking the study of Watson (2016) that found heart bars fitted with positive pressure helped in expanding contracted heels, there could be some benefit to positive non-deformable frog pressure in these cases, however this method would have to be compared to the application of frog support padding on the same type of foot to see the difference in efficacy.

On a day out with Mark Caldwell the author witnessed the heart bar used in a case that benefitted in the positive pressure.

Heart bar timeline shoe by Mark Caldwell fitted to a young horse who had caught its hoof in a gate and caused serious damage. The application was to stabilise and “clamp” the hoof reducing expansion and contraction to allow healing of the injury.

Images courtesy of Mark Caldwell.

Watson (2016) and the case from Mark Caldwell suggest that the heart bar still has its place in certain cases, carefully and deliberately fitted for a specific outcome, but the findings of Young (2018) and Casserly (2018) and the advancements in the treatment of laminitis perhaps point at the historical applications of the heart bar being obsolete in favour of more comfortable, deformable and functional frog support. Further then that the findings of Roepstorff (2001) suggest that in order to create an environment more similar to the natural bare foot, perhaps all horses should be shod in padding, perhaps the negative hoof morphologies that present due to the reduction in hoof function would reduce in number? Why do we wait till a hoof has a pathology to treat it with padding? Perhaps frog support padding should become as common as double clips fronts have as farriers look to provide optimal biomechanical and physiological function and be more pro-active. Whether the Heart Bar is obsolete or not, Farriers now have more options that are more practical and more functional, educated decisions need to be made what to choose when.

For any more information on the subjects and techniques addressed in this article please contact the author at

https://www.facebook.com/theequinedocumentalist/

or

https://www.theequinedocumentalist.com/

For more info on the frog support pads featured visit

https://www.facebook.com/the3rdmillennium/

For more info on Formahoof visit

https://formahoof.com/

References

Treatment of solar prolapse using the heart bar shoe and dorsal hoof wall resection technique

R. A. EUSTACE

M. N. CALDWELL

First published: September 1989

https://doi.org/10.1111/j.2042-3306.1989.tb02694.x

Equine Health

Vol. 2017, No. 38

Farriery

Sarah-Mary Brown

, frog better or worse,

Published Online:15 Nov 2017

https://doi.org/10.12968/eqhe.2017.38.18

Farriery Options for Acute and Chronic Laminitis

Stephen E. O’Grady, BVSc, MRCVS; and Andrew H. Parks, VetMB, Diplomate ACVS 2008 Vol. 54 AAEP PROCEEDINGS

Castalijns 2002

http://www.mascalcia.net/articoli/a2002_50.htm

Podol (2006)

https://www.americanfarriers.com/articles/6131-being-careful-with-heart-bar-shoes?v=preview

Reynolds, 2018, Personal Correspondance

Young , 2018 Personal Correspondance

Roepstorff, 2001, Myerscough Bsc (hons) Lecture

Watson, 2016 FWCF thesis list

Casserly, 2018 FWCF thesis list

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