In October 2021 I was lucky enough to attend the Centaur Biomechanics Equine Sports Seminar Virtual Summit. As always, the lectures were of a very high quality and there was an immense amount to take in. Here I share with you some of my understanding.
Haydn has been a practising farrier for 38 years and during that time has developed a special interest in performance and lameness shoeing techniques. An interest in research led to a number of projects looking at applied farriery and its effects on function. Haydn held the post of lead consultant farrier for 20 years to the British Equestrian Federation (BEF) and the World Class Equestrian Programme (WCP). He was awarded the BEF Medal of Honour in 2011 for his continued contribution to farriery with the BEF and the WCP, and was inducted into the International Farriery Hall of Fame in 2013 for his continued services, commitment, and education to the International Farriery Profession. Haydn has a particular interest in lameness and poor performance.
Haydn starts by discussing the point that in order to be able to manage something, you must be able to measure it. His focus is on developing repeatable processes, in order to be able to continue to learn from science, practice and experience.
Considerations in individual shoeing criteria are a multifactorial process. In the World Class Programme, this was particularly relevant. There appears to be a general view within farriery that foot placement is often the primary focus of how we shoe a horse. This doesn’t necessarily taking into account limb, joint and hoof capsule loading parameters. What are the factors that we can influence with farriery? In farriery, personal interpretation often comes into play.
Moving onto solar packing, Haydn explains that historically, solear packing was primarily defined as a form of protection. Studies looking at the effect of solear packing have greatly influenced our ability to prevent hoof capsule deformation and help stabilise the underlying structures. Currently, manufacturers make various claims about the benefits of some products, but there is not always science to support these claims. There is a difference between products, and more evidence is needed to demonstrate what the similarities and differences are.
Before we start to measure, we must measure normal hoof deformation during weight bearing. There is a theory that says that frog pressure is imperative to allow the well being of the hoof capsule and for the circulatory system. We now know that this is not the case, although there may be limiting factors.
Detailed knowledge of the anatomical position and function of individual structures is essential in maintaining soundness and performance. We need to know what happens to the internal structures if we apply packing, and we need to understand the effects of solear packing on hoof deformation. Reducing the hoof deformation can reduce the risk of injury, and of damage to the hoof structures.
Research has shown that we can have a dynamic influence on the hoof capsule and on the distal interphalangeal joint (the coffin joint). The question is, should we? There are a lot of competition horses who would benefit from this support.
All materials have an industrial ‘shore’ rating to establish tensile hardness. Different brands of solear packing have different shore ratings. In Haydn’s experience, top riders are often able to feel the difference in their horse’s performance with different brands of solear packing.
A study aimed to determine the effect of sole packing on hoof deformation and distal phalanx placement during weight bearing. The researchers used two different packing materials. The conditions that were calculated were barefoot, rim shoe, polyurethane sole pack (with a shore rating of 40), and a polyurethane impression material (with a shore rating of 28-30). Cadaver limbs were loaded into a hydraulic jig above a force plate, which enabled the forces through the limb to be repeatable. The forces applied were equivalent to mid stance weight bearing. Measurements were taken using X-rays, and the effect of packing materials on 3 dimensional hoof deformation was measured using a CT scanner.
The palmar proximal and distal hoof widths were significantly different between shoeing conditions in the loading limb, as you would expect. Differences between unloaded and loaded limbs in dorsal and palmar hoof widths were significantly different between shoeing conditions, the highest being in the unshod hoof, the lowest being in the shod foot with the impression material. The most significant measurement was the reduction in the height of the central sulcus from the weight bearing surface with packers. In this situation the frog is presumably experiencing immediate pressure during ground contact, the results of which suggest that packers, along with appropriate shoe profile, should be a consideration in clinical cases where stabilising the DIPJ during weight bearing is a requirement.
Reducing the hoof deformation can support the hoof capsule, and reduce the amount of displacement of P3 and the associated structures. Packing the upright foot in an asymmetric horse (a horse with one front foot flatter and the other more upright) can influence the asymmetry of the horse. To manage this, we need to be able to measure it, and this has been done. A horse with a more upright left fore showed reduced push off through the left fore with up to 64mm difference in head upwards movement, particularly on the right rein, without packer. This was measured using the Equigait system. With packer, all head and withers movement parameters indicated very symmetrical movement with between 0mm and 5mm average asymmetry and very symmetrical asymmetry between left and right rein. This needs researching in more depth. Currently, there does not appear to be any secondary pathology occurring, even in horses who have packing in one foot over a long period of time.
The effect of solear packing on P3 displacement has been measured. Packing reduces vertical displacement of P3, and creates a more forward displacement, which for some pathology could be beneficial. Research has been done into negative palmar angle and standard shoeing protocol of heel elevation. Originally, research has been done statically, rather than dynamically.
Graduated heel wedges are still the standard treatment intervention for negative palmar angle, but this approach is contraindicated for a return to normality for the horse. A 2004 study found that there was a direct correlation between heel angle and forces exerted on the navicular boat and distal phalanx during weight bearing.
In a study, limbs were randomly selected, placed into a hydraulic testing jig, and vertically loaded above a force plate to 10 N/kg body mass. A 28 shore rating impression material was used to give caudal support via polyurethane impression material, with a concave rim shoe and thermoplastic hoof shield. This was compared to a standard heel lift of the Stromsholm 5 degree graduated heel wedge. A number of parameters were measured, including joint positioning and orientation. There were no significant differences between conditions for any of the parameters except for the moment arm of the deep digital flexor tendon (DDFT) at maximum fetlock hyperextension, which was reduced with the packing material. Therefore with the packing material, there was less strain through the DDFT. The key to rehabilitation of soft tissue injuries may be to influence the individual joint moment arm, rather than heel elevation alone.
Take home messages:
For more information, great webinars and a whole heap of relevant research, visit www.centaurbiomechanics.co.uk.
© Sue Palmer, The Horse Physio, 2021
Treating your horse with care, connection, curiosity and compassion
