Navicular

 

Dr Bowker's latest work has put navicular problems down to vibration destroying tissue in the foot. He described the digital cushions of navicular horses like 'hamburger meat' because the microvessels had been obliterated. He says that damage occurs to the tissue in the digital cushion and lateral cartilages first and then damage migrates from here into the Deep Digital Flexor Tendon and navicular bone. Stating that navicular is an entire foot problem. In these studies, all horses had very weak thin lateral cartilages and no structure to support the back of the foot. He concludes that the vessels within the digital cushion and lateral cartilages have been destroyed by vibration and this is the biggest factor in navicular horses. He also pointed out that lateral cartilages and digital cushions were not small because of lack of development but small because they had degeneration and being severely affected by vibration.

 

Rooney, Bowker, and Pete Ramey have all, in turn, put the blame on vibration in some way or another. There are several shocking studies which confirm this, Luca Bein who in 1983 found that the horseshoe vibrated at 800Hz which will damage blood vessels and live tissue. A study in Holland carried out more recently, showed that a horseshoe can vibrate up to 2500 Hz. Which is really concerning considering that vibration as low as 250 Hz can destroy connective tissue. Vibration damage in humans is well known and in many professions such as dentists, Joiners, Loggers, Gardeners, and Farriers all are known to suffer from tool vibration damage where they have capillary and nerve damage which leads to circulation issues and numbness. The vibration of a horseshoe when a horse is used on a hard surface is comparable to these professions tool use. It is fair to say that this navicular damage can come from toe first landing of a shod or unshod horse, and now after Bowker's finding vibration of a horseshoe as well. Dr James Rooney says it is clear that the earliest naked eye evidence is the navicular cartilage turning yellowish brown and also often translucent. Lesions also appear on the distal ridge and it has a greater curvature from wear. The yellow discoloration is a result of structural change in the cartilage and this discoloration also happens to the deep flexor tendon. It’s not clear what this colour change is, but It’s fair to surmise like Rooney that this structural change is the fibrocartilage reacting to vibration and friction damage. He basically proves this by exposing heat to cartilage and getting the same yellow discolouration.

 

Dr James Rooney first looked into navicular problems over 40 years ago and published a paper in 1974 that basically said that navicular was not a disease.  This was because in all the navicular horses he tested there was always damage to deep digital flexor tendon and not always damage to the navicular bone. So Rooney suspected a biomechanical issue and proved his point by building a machine that emulated toe first landing which reproduced the same damage known as navicular. Although Rooney believes the real damage to the surfaces of the navicular and the deep flexor tendon is irreversible, developing the digital cushion of a horse and facilitating heel first landing will give it the structure and protection it needs to be able to become perfectly sound. The point being that the bone damage on the navicular bone is the result of a biomechanical problem and not the actual cause of the pain. Hence, it was pain that force the horse into a toe first landing and not the other way round. There maybe sometimes a deterioration in the navicular bone itself, but by developing the back of the foot the digital cushion will directly support the navicular area and cure any lameness issues.

There are no tricks here, there is no changing of gait, or artificially supporting the back of the foot. It is about simple biomechanics, trimming to the internal structures to facilitate heel first landing and removing any interference to encourage natural movement. Pete Ramey explains how a toe first landing effects a horse.” In a toe first landing, however, the descending fetlock joint is still tightening the tendon just after impact, but after the toe impacts the ground, then heel rocks downward, tightening the tendon at the same time. Understand that in a heel first landing we have one pulley tightening as the other is releasing tension, but with a toe first landing, both pulleys are tightening at the same time. Far greater force is directed to the navicular pulley than was ever intended by nature.” Treatment of caudal heel pain is relatively straightforward. Softer conditions are needed at first because on hard surfaces there is no relief of this tension while any part of the hoof is still on the ground, in softer conditions the toe rotates into the earth prior to the heel lifting and thus reduces this tension. Developing the back of the foot is done by gradually lowering the heels and allowing some frog pressure. The horse must remain comfortable and heel first landing is paramount. Boots and pads with inserts are a great tool for these horses helping to stimulate frogs and also protect at the same time while encouraging as much movement as possible.

 

There is no doubt in my mind that vibration of the horseshoe is the main cause of this problem. I think that road work and horseshoes will cause the vibration damage seen in Dr Bowker’s paper very quickly and toe first landing will exaggerate these issues. Therefore, to prevent issues, owners should not have their horses shod to use on roads. Ironically this is the main reason most owners shoe their horse in the first place. Also, if their horse is shod they should keep them off roads as much as possible and only at no other gait than walk. It is obvious that the back of the foot issues come first in navicular cases, which then force a horse into a toe first landing. These back of the foot issues could be as simple as thrush and any issue that forces a horse away from their natural heel first impact should be addressed as quickly as possible. Therefore, it is advisable to check a horse’s gait regularly and learn what a natural heel first landing looks like.

 

© Copyright 2015 Chris Simpson

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