• theequinedocumentalist

The Bearing Surface- Creating optimal basal support

Updated: Feb 7

The digit is on the end of the limb, the limb is attached to the body and all this weight is transferred through the hoof. Creating a bearing surface that allows even loading of the limbs helps to protect the musculoskeletal structures of the entire horse. The weight of the horse is transferred through straight gravitational lines down the limbs. Putting the heels of the hoof, the toe and everything in between, in the right place and putting a shoe on that compliments the horses’ conformation provides the limb with a base that can best support that load, statically and dynamically.

Uneven or excessive loading will predispose the horse to injury and degeneration of structures throughout its entire musculoskeletal system. The horse has different stages of locomotion. In this article we will mainly be focusing on the benefits of achieving static and mid-stance basal support.

Studies have shown (Caldwell 2016) that every horse should be assessed on an individual basis and shod according to its unique physiology to achieve the best balance. Here in lies the secret to a good shoeing job, not only looking at the external structures of the bottom of the foot, but the entire horse, its age, work and musculoskeletal system, as workload, conformation and physiology directly affect the hoof (Curtis 2002) and the hoof directly effects the entire anatomy (Kilmartin 2014). Balchin (2017) outlined the fact that maths should be the basis to any shoeing job, one of the fundamentals talked about was the importance of trimming the heels back to the highest, widest part of the frog to establish the correct ratios of the solar plane.

Fig1-2. When a horse is shod, the bearing surface of the foot becomes the shoe. In the before pictures the heels are way forward of the widest part of the frog and the shoe followed, this caused the bearing surface of the foot to be forward, the centre of pressure (CoP) moves dorsally and the internal structures are under increased strain. Simple hoof growth over a shoeing period will create this effect.

Re-establishing the dorso-palmer bearing surface is as important in everyday shoeing as in remedial shoeing as many studies have shown that hoof morphology has a direct effect on the internal structures of the hoof (van heel et al 2004,2005). These studies showed that the forward migration of the hoof puts strain on the flexor structures and the navicular structures. The re-establishment of the bearing surface through trimming to the correct protocols and shoe placement that compliments this trim, giving full caudal support to the hoof, will put the CoP back to a more ideal position.

As well as static load the bearing surface has dynamic implications too, Van Heel et al (2004) observed a trace followed by the majority of horses (Fig.3).

Fig.3 The trace of the CoP during locomotion.

Van Heel et al (2004) Discussed how post trim there wasn’t a substantial change in how the hoof landed but it did affect other aspects of the stride. Most markedly how long a hoof took to land was reduced, leading to the hoof having complete bearing support sooner, subsequently the CoP moved centrally quicker which in theory positively effects the load distribution on the internal structures.

Conversely this study shows that hoof growth has a negative effect. The hoof takes longer to reach full bearing, meaning the caudal aspect maintains loading for longer and at full bearing the load would be more medio-laterally imbalanced, again negatively effecting the surrounding internal structures. Van Heel et al (2004) added that full bearing support is also beneficial in absorbing concussion.

Moleman et al (2006) added to the findings of Van Heel et al (2004) showing that in a shoeing interval of 8 weeks the hoof wall angle decreased significantly, this in turn increased the moment force significantly around the distal interphalangeal joint (DIPJ) however the moment around the proximal inter phalangeal (PIPJ) joint did not change significantly. This showed a compensation for the change in hoof conformation happened mainly in the DIPJ, the extension of this joint created an increased load on the deep digital flexor tendon (DDFT) and the navicular area, predisposing these soft tissue structures to injury.

This showed that although the horse can compensate to an extent for hoof growth this compensation is detrimental even with minimal hoof growth and farriery intervention is important in protecting the internal structures of the hoof.

Moleman et al (2006) showed that there was no significant difference in the change of the CoP in a high angle foot (HHA) to a low angle foot (LHA), but the increase in moment was 2.4% larger in the LHA around the DIPJ, this indicated that horses with high-low conformations should be shod according to the needs of the LHA and horses with LHA in general require re-establishment of their bearing surface sooner. In another words, the flatter your horses feet, the shorter shoeing interval they need. As opposed to "he doesn't grow much we should leave him longer".

The ground reaction force (GRF) did not significantly change over the shoeing period in Moleman et al (2006), this indicates that the horse did not change its centre of gravity, however the distance between the GRF and the centre of rotation did change, indicating that the change in the lever arms was directly due to the change in the angles of the joints. Even with a shorter shoeing interval the changes in hoof angle have a detrimental effect on the underlying structures.