The United Kingdom Horse Shoers Union

The voice of the farrier.

Posterior Third Lameness.

A series of articles by Peter N Baker.

An in depth study of posterior third lameness of the equine front foot. To a greater degree a predictable condition, which by good farriery, husbandry and attention to hoof capsular shape can be arrested if not reversed.

Part One: Hoof shapes and their locomotive roles.

Contents:

1. Introduction.

2. Definition of Posterior Third Lameness.

3. Propulsion loss.

4. Bilateral capsular changes.
(i) Bilateral hind limb disfunction.
(ii) Sloping pasterns.
(iii) Upright pasterns.

5. Unilateral capsular changes - unilateral hind limb disfunction.

Introduction.

During the course of the last two decades the author has been fortunate enough to work on a number of horses, many of which were referred, having experienced a period of prolonged hoof capsular imbalance. It was noticed that the longer the animals had worked in an unbalanced state the more complex the degenerative changes within the horse had become. A distinct pattern emerged regarding the progression of the above changes, which appears to relate to the time the animal had experienced the imbalance. In this paper an attempt is made to chronicle the progressive nature of the said changes from the initial imbalance up to the point of irreparable arthritis; and to identify which steps taken by the farrier seem to ease the discomfort suffered by the horse. It seems that at any stage of the progression, imbalance
correction, to a lesser or greater degree will reduce the animals suffering.

It will be suggested that posterior third lameness is not a single condition, but that it is simply a progression of well documented lameness conditions found in the horse.

Researchers into the causes of lameness conditions will have experienced difficulty. Standard texts do not link the development and progression of the conditions, and appear to conflict with the latest understanding of anatomy and hoof dynamics.

Definition

Posterior third lameness is a pain condition found in the rear third of the of the equine front foot, which cannot be easily explained. The pain will block out with a local anaesthetic. Further blocks may show that there is an involvement of one or more limbs in this condition.

Propulsion loss

Radiographs and autopsy specimens of specific and detailed cases determined that the initial injury had been to the hind limbs and in particular the hock. The initial involvement of the front feet was probably a secondary effect, and only later did it become a syndrome in itself.

It will be necessary to consider the primary insult sites to establish whether one or both hind legs are involved.

Bilateral capsular changes

(i) Bilateral disfunction
It was concluded from the above cases that the indicators of bi-lateral hind leg malfunction are the apparent "tieing up" of the animal after strenuous exercise, a heavy shoulder, a high slamming front leg action, a flat foot impact, a radiused toe wear, a general overall flattening of the worn shoe, a predisposition to stumble, an abnormal heel development resulting in contracted narrow folded under-run heels, and an expanded open toe which is predisposed to
laminal stretching.

(ii) Sloping pasterns.
It is noted that weak or rear end impaired horses that move this way, that are disposed to having sloping pasterns, tend to develop a short wide front foot, the heels of which are under-run, weak and folded, compressed and saturated. This animal may show wear to the extreme ends of the heels of its front shoes, with the overall flattening previously mentioned, as opposed to the radiused front toe wear seen in the normal or upright pasterned animal.

A study of morbid specimens of a horse affected with this type of open front feet showed a flattened triangular shaped area, the apex of which extended up the dorsal wall as far as the extensor crown. This flattened area probably comes as a result of laminal disruption, resulting in cavitation under the wall. The resulting defect of the laminal bed probably accounts for the chronic toe cracks, dorsal wall defects and seedy toe which are not uncommon in equines that
have flat front feet.

(iii) Upright pasterns.
There seems to be a marked difference in bi-laterally affected horses with upright pasterns, these animals do not develop the short wide foot described above, their front feet become narrower, their heels pull in. The solar plate thickens, becomes convex, and is reluctant to exfoliate in the normal way. The strong solar plate seems to force the toe area of the hoof capsule forwards, causing it to turn upwards, this action stresses the white zone and a cavity may form in the solar toe area of the capsule.

A study of a radiograph of a distal phalanx of a horse suffering from this condition revealed a chronic loss of bone in the solar toe area. This animal had suffered from a long period of posterior third problems.

It must be noted that in the above text, the feet referred to are co-laterally matched, that is they are pairs.

During the period 1988 - 1992, when the bulk of this study was undertaken, the progress of three bi-laterally collapsed heeled horses was closely followed. the three animals did not respond to any method of therapy used to try and effect heel development. Two of the animals were destroyed after developing into wobblers, both were put down following isolated incidents leading to their deaths. In fact one collapsed in between hurdles on the race track, the other fell on the gallops after whipping around and was unable to stand up afterwards. It was quite interesting to note that there was no major impairment of their forward speed. The third horse showed signs of mild inco-ordination of movement before being exported to the USA.

The three animals referred to above would indicate that there is an involvement of a back problem in the syndrome of bi-laterally collapsed heeled front feet. Rebalancing the feet of the animals did effect some pain relief, although short periods of intermittent front foot lameness was seen.

Unilateral capsular changes - unilateral disfunction.

(i) The hock.
The first is quite straight forwards - the involvement of the hock whether it be soft tissue damage, or bone fusion (spavin ). Both of these conditions impair the function of the limb and alter the way the animal propels itself along. Both at the acute stage when pain is the relevant factor, and at the chronic stage when bony changes have taken place. (Once ossification is complete a mechanical disfunction will be noted).

The indicators of this condition are uneven hind shoe wear, not unusually a scuffed out toe and a general graduating wear pattern from toe to heel. It does not follow that this pattern of wear will have taken place equally on both sides of the shoe. In fact in cases of one sided drive unbalanced graduated shoe wear is a normal process. A unilateral neuro-muscular response may be noticed when the leg is lifted (snatching up and quivering).

At the acute stage there may be a positive response to a spavin flexion test. Close examination
of the central tarsal bone and its joint may show some swelling or bony enlargement.

(ii) Pelvic rotation.
One hip will drop due to its support structures being damaged and the attendant muscular shrinkage. This is a common injury and mostly comes about when the animal partially slips over and its weight falls on one of its hind limbs causing a strain of its lumbosacral joint, (Jenny Hall, Lambourn, personal communication). Following the initial insult the resulting
pain causes lameness, the injury will probably lead to ligament damage, the limb appears to drop and muscle shrinkage is seen. In time the pain subsides and healing takes place, repair will eventually be complete. However due to gravity the pelvis will not return to its previous position, and will remain rotated. This leads to an uneven rear end drive. The uneven shoe wear will again be noticed, one hip will be seen to be lower than the other and the other hind limb will have a wide carriage. The animals back will be off set to the direction in which the animal is travelling, however the head and neck will face directly ahead. The limb which is carried the lowest will be carried under the animal’s central balance axis and will impart relatively more drive than its collateral. The diagonal front foot will assume the natural leading role. In the circumstances laid out immediately above, the hoof capsule of the lead leg will over a period of time change its form and become an open flat weak heeled type of foot. Its co-lateral will become a narrower and more upright distorted type of hoof capsule, and assume the role of being the weight bearing support leg. This text refers to these as being a mismatched pair.

Three types of hoof capsule are readily identifiable.
(1) The upright tight heeled foot.
(2) The flat open type of foot.
Both of these types have been described above.
(3) The hybrid foot. This relates to a medial - lateral imbalance and will be discussed at length later in this series of articles.

At this point it is only fair to assume that the loss of rear end drive power necessitates the animal to change its way of moving, and to a lesser or greater degree to pull itself along with its front limbs. This modification of locomotion, and the resulting action change causes the heels to drive forwards, displacing the horny mass of the solar plate forwards. In turn the solar plate shunts the distal border of the wall, and this motion will cause the toe to turn upwards, effecting a condition referred to as dorsal depression (Bailey, Louisville 1988).

Having established the hoof capsule shapes and their locomotive roles, the next article will look at the internal changes which result in a shortening of stride and an "ouchy" progression.

First published in Forge Magazine 1997. Copyright Peter N Baker.