Dorsal Wall Lifting

Posted on September 20, 2019 by Jerrilee.
Categories: handicap, health, history, hoofcare, therapy.

Theory of laminitis explained

(exerpts from: equinehoof.co.uk)

The easiest way to explain this new model for laminitis is to look at the hoof as a simplified structure, broken down to its basic components, this enables an easier understanding of what is happening.

Fig 1: Normal hoof section growth

Fig 1: Normal hoof section growth
Fig 2: Chronic laminitis hoof section growth

Fig 2: Chronic laminitis hoof section growth

To examine the effects of normal and laminitic hoof growth, a flat rectangle of hoof can be used to represent a section of hoof (Fig. 1), as new horn is produced in equal amounts on each side of the rectangle, the hoof section grows without distortion.

When laminitic hoof growth is examined in the same way, one side of the hoof is growing faster than the other, horn produced under these conditions will grow in a curved or distorted manner (Fig. 2), the lower extremity of the horn will be deflected forward.

By increasing the complexity of the model to a simple hoof capsule consisting of three sides, a front or dorsal wall and two sides that represent the medial and lateral quarters, we now have an approximation to a hoof capsule.

In the normal simplified hoof the dorsal and quarter areas are growing at similar rates and the hoof grows down in a consistent way (Fig. 3).

Fig 3: Normal hoof capsule growth

Fig 3: Normal hoof capsule growth
Fig 4: Chronic laminitic hoof capsule growth

Fig 4: Chronic laminitic hoof capsule growth

In the laminitic foot the quarter areas are growing faster than the dorsal wall and the hoof grows in a curved manner to accommodate this difference (Fig. 4). The dorsal wall now has a dished dorsal surface, caused by the curved shape of the medial and lateral walls deflecting the dorsal hoof wall forward.

A revised interpretation of acute Laminitis

It is proposed that when a horse encounters a systemic disease that is known to cause laminitis, one of the first events will be an increase in rate of growth at the quarters (Fig. 8).

Fig 8: Simple acute laminitic hoof capsule model

Fig 8: Simple acute laminitic hoof capsule model

This increase in heel growth does not initially cause pain but eventually after a period of time, which may be hours or several days, the hoof capsule will distort beyond the limit that can be tolerated by the laminae. The distorting hoof capsule will then traumatise the laminae and tissues that are situated between the hoof and distal phalanx (pedal bone). In the early stages, any hoof distortion may not be obvious to the naked eye but at a laminar level it will cause pain. (Fig. 9).

Fig 9: Acute laminitis hoof capsule growth

Fig 9: Acute laminitis hoof capsule growth

This delay between the triggering event and the onset of pain is consistent with a developmental or pre-acute phase of laminitis, while the trauma induced in the sensitive tissues will cause the symptoms that have previously been identified as a vascular crisis.

In the early stages of the acute phase, distortion will be concentrated at the distal border of the dorsal hoof wall. As the heels continue to grow the dorsal wall will be elevated away from the distal phalanx in a peeling motion as the distortion migrates up the dorsal wall (Fig.10 – Arrow B). Peeling provides a better explanation for the separation observed between the distal phalanx (pedal bone) and the dorsal hoof wall, it is the most efficient method of mechanically separating two strongly bonded surfaces and requires less force, peeling would also be very painful. When the peeling process has separated enough laminar attachment, the distal phalanx will be detached from the dorsal hoof wall.

As the distal dorsal wall is lifted, the solar horny plate will be pulled upward towards the distal border of the distal phalanx. This upward movement of the horny sole will compress the solar corium, causing pain within the solar corium and compromise blood flow by entrapment (Fig. 10 – Arrow C). Bruising is often subsequently seen in this area of the sole after laminitis and is evidence of this trauma to the solar corium.

As the distal dorsal wall is lifted, the proximal border of the dorsal hoof wall will be pressing inward, again causing pain and compromising blood flow (Fig. 10 – Arrow A). Horn growth at the proximal border of the dorsal hoof wall is often restricted in severest forms of acute laminitis.

Fig 10: Acute phase - Hoof distortion

Fig 10: Acute phase – Hoof distortion
By including the hoof capsule in a causal role in laminitis, the qualities of the hoof can be seen as influencing the intensity of pain felt by the laminitic animal. The level of pain experienced during the initial phases of acute laminitis can be correlated to the shape and strength of the hoof capsule. In round feet, hoof distortion will spread from the toe medially and laterally towards each heel, causing the whole hoof to expand open, this will predispose the distal phalanx to sinking as a greater area of laminar attachment is lost. Long narrow hoof capsule shapes will tend to predispose the foot to rotation as most of the distortion will be concentrated at the toe of the hoof.

This new interpretation of laminitis is still in it’s formative stages, it is hoped that further research will be directed toward confirming that this model is a more accurate account of the changes seen in the feet of equines suffering with laminitis. Time will show how accurate this proposed model is. Whatever the outcome of this research, we must continue to look for ways to help the laminitic equine.

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