Evidence Based Podiatry
Farriery has, up till recently, been largely based on anecdotal evidence and experiential opinion. We are entering a new era of evidence-based research into farriery interventions, what is the research telling us? How do we extrapolate practices for our daily work?
Firstly, it’s important to highlight that when it comes to research, single studies often only show a truth for a certain population at a certain time and according to the protocols that study used to gather its information. Very importantly studies are subject to the way the author analysed the data collected and what conclusions they came to, this always needs to be critically appraised. One needs to use ones own critical thinking to dissect the studies and decide if what it said the data shows is actually logical. What is more powerful, is when you start to get groups of studies that point toward the same set of logical principles. That’s when you can create logical implications for daily practice.
When you start doing that, you still need to apply those principles correctly and gain practical experience as to what theories stand up in practice. The reality is that with podiatry any theory is only as good as the application of that theory. As much as knowledge can point toward certain practice, practical skill will always be a limiting factor in its efficacy.
Take wedges for example, something widely debated in the industry. Many people and some studies have suggested that they crush heels. Weller (2020) discussed this very recently, we know that the point of force is moved toward the heels with wedges (Wilson et al.) and the length of time that the heels are loaded through the stance phase is prolonged. So, people logically extrapolate that the heels will suffer as a result, but, Weller also discussed how moving backwards of the point of force, reduces the extensor moment and therefore reduces the strain on the flexor structures.
Fig.1 Schematic illustration of the movement of the point of force (PoF)or centre of pressure (CoP) with elevation of the heels. A reduction in extensor moment arm = a reduction in flexor structure strain.
If we provide adequate frog support, length and get the wedge fitted correctly it has obvious benefits for certain horses, fitted wrong without consideration for the consequences, it does perpetuate the conformation that leads to their need in the first place. In the authors experience, if they are fitted with certain important factors in place, that risk is mitigated and they become a very useful therapeutic and transitional tool as you begin to see improvement in the heels.
Fig. 2 Schematic diagram of a well fitted wedge vs a poorly fitted wedge. With every application the efficacy is often subject to correct application.
The point is that we need to critically appraise both theoretical sides and balance them with real world experience and logic. For instance, using the same subject, one of the biggest problems with studies that have suggested an increased intra articular pressure and increased load on the other flexor structures with wedges, is that they didn’t established an ideal. They are telling you that the numbers change, but without an objective quantification of what the intra articular pressure should be, how can one establish whether to attribute a positive or a negative to the change in pressure. When you put these findings against the studies that show the predispositions of broken alignment, you then have a balancing act to work through to decide your own practice. For me the catastrophic injuries associated with poor alignment outweigh the risks of heels being crushed, especially when those risks are mitigated and In practice i have actually found the opposite to be true.
So that’s the process that one has to go through with the research, take the studies that may even be opposing and work through them. Try to establish what can actually be gleaned from them and what makes logical sense. You can’t take a single study and especially the authors interpretation of its data and just use that one finding to dictate your daily practice.
Another really good example, in my opinion, for this process of critical appraisal is a recent study, Craig (2020). It took thousands and thousands of x-rays and found that perfect alignment was very rare. Something that the author would agree with from real life experience and something that other studies have confirmed (Dyson 2011, Clements et al. 2019) .
The question is what do these studies tell us? Is common correct?
looking at Craig (2020), I would come up with a different analysis of the same study, and this is the problem with science, in inverted commas, because the data is the data but the interpretation of the data will always be somewhat subjective. Some people use that study to imply that aligned is not correct and perhaps we shouldn’t aim for it. But I question, is it saying that, or is it saying we have an issue that needs addressing? considering we also know that caudal hoof failure is found in as much as 75% of the shod population and is directly linked to lameness (Dyson 2011). These findings also raise other questions, where do we draw the line between acceptable natural variation and something that predisposes to pathology, especially in the light of all the other studies that clearly show a relationship between poor alignment and navicular for example.
Weighing up individual studies against the wider literature helps to guide practice. For the author this has led me to choose a practice that looks to establish as straight a hoof pastern axis and near straight phalangeal alignment as is sensibly possible, or at least work towards it. If we aim for aligned we will probably miss it by a working tolerance, if we use such studies to disregard alignment as a result of bio diversity without assessing the individual cause, then for me that becomes dangerous. Podiatrists don’t have the luxury of radiographs before and after every job, however, a straight hoof pastern axis is easily recognisable. A straight hoof pastern axis externally will usually still be a few degrees out at each joint of the digit. If we don’t aim for a straight HPA then how much more would those angles be out. The point though of all that is that we need to use our own critical thinking and logic to firstly question the reliability of and then correctly apply a studies data before we just accept the authors interpretation.
Podiatrists should have groups of studies for different aspects of podiatry that compliment each other and point toward certain logical principles.
There are different aspects of podiatry that need to be considered and a library of studies utilised to build practical principles from.
The following are my principles for daily practice.
Hoof Function, Boney Alignment and Biomechanical considerations.
Taking the studies into the barefoot and its function can act as a blueprint for what would be ideal functionality. Nature and evolution has had thousands of years to create something that works, so we should try and replicate that.
lets start with Hoof wall biomechanics. How does the hoof capsule work and move/flex and distort? The studies of Thomason et al., specifically the study dating back to 1992 showed us how the hoof naturally distorts.
The hoof wall is an obliquely truncated cone that opens posteriorly between the heels. The wall has to withstand two types of loading: high-velocity impacts with the ground and transmission of forces between the ground and the skeleton. The deformation of the hoof is therefore very important in absorbing concussive forces. The distortions that were documented were,
• Inward Movement of dorsal wall
• Expansion of heels
• Depression of coronary band
• Sinking of heels
• Flattening of sole
• Biaxial Compression of Dorsal Wall
Fig. 3 The natural viscoelastic deformation of the hoof.
If we look at the old studies of snow and birdsall (1990) suggesting A change in hoof shape may be the result of a shoe restricting normal capsular deformation, which was recently cited by Dyson (2011), which was looking at essentially caudal hoof collapse, we can see a logical link between this natural viscoelastic deformation and hoof proportions and health. This was also suggested by Gunkelman and Hammer (2017) who stated the ability to efficiently dissipate the forces of locomotion directly affects hoof morphology.
We can put these studies together with the studies of Bowker and Poss on haemodynamics. Bowker has discussed 3 theories for how the haemodynamic system works, to briefly outline them there is the depression theory, compression theory and the negative pressure theory. One of those theories state, displacement of the digital cushion presses against the lateral cartilages and subsequently compresses the vascular structures. Another theory suggests the descension of the middle phalanx induces an outward displacement of the lateral cartilages, this theory is somewhat backed up Taylor et al (2005) which indicated that the function of the digital cushion was mainly to counteract this displacement of the middle phalanx and not to provide a pressure force.
Bowker suggests another theory, “When the foot hits the ground, the bars of the heels and pillars of the hoof wall force a small “shelf” of the cartilage outward, creating negative pressure in the digital cushion. Impact is thus transmitted to a complex venous network inside the cartilage, creating more negative energy, which draws blood up from the solar area of the hoof.”
Fig. 4 The traditional haemodynamic theories.
Which ever theory one accepts and perhaps all are true, what we can take from this is that the caudal structures of the hoof are important in dampening the forces of impact AND responsible for aiding the natural deformation, which in return is important for the correct morphology of the hoof.
So what does this have to do with shoeing and how do I address this in daily practice. Well if you look at those studies and combine them with the Roepstorff (2001) study which showed that the expansion in a shod foot was restricted compared to a barefoot but frog support padding returned functionality to the foot closer to that of the barefoot. Then you add the studies showing the improved morphology of feet taken out of shoes by Clayton, Malone and Davies and Proske it all starts to point toward caudal hoof support being an important factor in a functionality and therefore a healthy hoof. Going back to Bowker who also spoke about the difference between a strong and weak foot this tells me that in daily practice, weaker feet need this support even more so.
So to conclude that section, by looking at the functionality of the bare hoof and the impact of shoeing and non-frog contact, when a horse cant go barefoot, which is a debate for another time, then I want to provide the same functionality as close as I can by providing frog support padding.
If you reverse engineer the positive morphology of going barefoot, and consider that weak caudal structures will fail, we then see how the correlation of the health of the caudal structures, namely the heels, directly affects the hoof proportions, toe to heel ratios and therefore alignment. Which brings me onto my next aspect of practice.
Going back to the study I mentioned suggesting alignment is not normal or ideal and other teachings that talk about the ideal of a ground parallel pedal bone, this has created a lot of confusion about phalangeal alignment and hoof pastern axis. The amount of peer reviewed evidence-based studies to agree with these suggestions are limited, however there are a substantial amount of agreeing papers that outline alignment as an ideal and discuss the predispositions of a broken alignment. Even breaking alignment from hoof growth was outlined as having negative implications.
Moleman et al (2006) showed that hoof growth broke the HPA and increased the moment arm around the distal interphalangeal joint (DIPJ) surmising that the effects of a Broken back HPA (BBHPA) translate into increased load onto the DDFT, distal phalanx and DIPJ structures. Earlier studies also showed similar effects of hoof growth in breaking the HPA and the corresponding negative correlation biomechanically. Van Heel et al (2004,2005) and Moleman et al (2006) findings highlighted the effects of hoof growth on both biomechanics and soft tissue load.
Clayton (1990a, 1990b) showed the increase in breakover time of the fronts and hinds with a BBHPA and an increase in toe first landings in the forefeet.
A straight HPA has been described as important for optimum bi