Unilateral laminitis
Laminitis induced by heel trimming of upright feet
Generally laminitis is considered to be a systemic
disease which affects all feet, with the front feet being most commonly
affected. This pattern of a general systemic condition does not explain
why only one foot should become laminitic.
I would like to highlight a cause of laminitis which means that we will have to make
changes in the way each new case of laminitis is assessed. At the core
of this model is the relatively rare condition of unilateral laminitis,
this condition has always been surrounded by inconsistency as it does
not fit the usual pattern found in laminitis. |
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Sequence of events in Unilateral Laminitis
- Unilateral flexural deformity of the
DIP joint as a foal
- The horse matures with the flexural deformity untreated or unresponsive to
treatment
- At a later stage (usually in the first years
of being shod) the heels are lowered to 'improve' the appearance
of the foot
- Unilateral laminitis is usually observed
about 6-12 months after heel lowering commenced
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| Unresolved flexural deformity of the DIP joint
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Fig 1: Bilateral flexural deformity
of the DIP joint |
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A possible cause of unilateral laminitis can be found in
the clinical histories animals which have had the condition ‘flexural
deformity of the distal interphalangeal (DIP) joint’ (Fig 1). This is
commonly known as ‘contracted tendon or ballerina syndrome’ by the lay
horse owner. The instigating causes of flexural deformities are
uncertain at the present time but it's not a contraction of the tendon. A popular current theory being an increase in the rate of
growth in the physis or growth plates of the bones of the distal (lower) limb,
while the associated deep digital flexor tendon does not grow as quickly. This differential in growth
within the structures of the limb result in the foals’ foot having a
more upright posture than normal. Some foals are born with a congenital
form which is considered to be abnormal muscle contracture.
In severe cases the heels will not
touch the ground as the flexor tendon is shorter than its associated
bone structure. These cases are easy to recognise and are usually
referred for veterinary treatment. Less severe cases can go unnoticed,
particularly if both forelimbs are only slightly affected. Generally
foals do tend to have more upright conformation, making the
identification of the milder cases very difficult.
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| The quality of life for mature
animals with a history of flexural deformities has not been well
documented but some of these horses will mature with a legacy of
flexural deformity of the DIP joint, the condition either not responding
well to treatment or has not been recognised at all. These mature
animals will have a more upright than normal conformation in one or more
limbs (Fig 3). |
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Fig 2: Evenly loaded
upright conformation |
| 'Mismatched feet' |
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| Problems can arise in the mature
horse, when the foot’s upright posture is seen as unacceptable and the
heels are lowered to ‘improve’ the appearance of the foot, in the belief
that by introducing the frog to weight bearing, the foot will become
more open and less boxy (Fig 3). As in the foal condition the heels may
have very little ground contact, as the length of the deep digital
flexor tendon will not permit the heels to descend fully to the ground.
In these cases the hoof capsule is now disproportionately loaded on the
dorsal wall and mechanical failure of the laminar attachment is not
uncommon in this situation (Fig. 4). In the early stages laminar
stretching will become visible on the solar foot surface and
intermittent lameness, particularly on hard surfaces, will become
evident. Gradually hoof distortion becomes established and the foot
takes on the appearance of a typical laminitic foot, with diverging
growth rings at the heel and a distorted dorsal hoof wall, while the
sole becomes convex displaying a typical ‘dropped sole’ (Fig 5).
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Fig 3: Naturally upright
foot or 'Mismatched feet' |
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foot will have all the characteristics of a conventional laminitic foot
and will be treated as if it were a typical case of laminitis.
Radiographic examination will show the distal phalanx appearing to be
‘rotated’. Further heel lowering in an attempt to ‘de-rotate’ the distal
phalanx will be futile, bearing in mind the deep digital flexor tendons
involvement, and will probably make matters worse as this induced the
laminitic condition in the first place. |
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Fig 4: Overloaded dorsal
wall after heel lowering |
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Unilateral laminitis
Once unilateral laminitis becomes
established the condition is easily recognisable, the coronary band
often dips lower at the toe and the heels are deeper than normal with
diverging growth rings. The naturally more upright position of the
distal phalanx will leave the distal border vulnerable to excessive
pressure which often results in remodelling of the distal border or ‘slippering’,
while the other three feet will be perfectly normal, showing no signs of
laminitis.
Bilateral mechanical laminitis
Horses with bilaterally upright feet can
develop laminitis when the heels on both front feet are lowered. Over
time the symptoms associated with laminitis will become visible, the
feet looking essentially the same as in ‘normal’ laminitis, but there
will be no evidence of an underlying systemic disease. Laminitis caused
in this way could truly be described as mechanical laminitis, caused by
mechanical changes in the way the hoof capsule was loaded during weight
bearing.
Many farriers will find the concept of
laminitis being induced by heel lowering difficult to come to terms
with, as it will shift some of the responsibility for the inducement of
laminitis onto the farriers’ shoulders.
This unrecognised cause of laminitis demands a
major rethink on how we look at laminitis in general, because now there
are two distinct laminitic groups, ‘normal’ laminitis and a sub-group of
laminitis cases induced by heel lowering in a previously upright
conformation. |
Fig 5: Unilateral
laminitis or club foot |
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| Fig 6: Upright
confirmation before and after laminitis |
Fig 7: Normal confirmation
before and after laminitis |
| Identifying this sub-group of laminitic cases
is vitally important from many viewpoints. The methods used when
trimming laminitic feet will have to be reconsidered, as heel lowering
is implicated in the onset of this type of laminitis. The interpretation
of radiographs is also complicated by this concept, it can’t be taken
for granted that the original position of the distal phalanx was at a
normal position before the onset of laminitis, it may well have been at
60 degrees or higher (Figs 6 & 7). Therefore trying to reduce its angle
will be impossible as the deep digital flexor tendons length prohibits
the distal phalanx being positioned at a normal angle. |
| It is because bilateral laminitis caused in
this way looks essentially the same as systemically induced laminitis
that it has remained undetected for so long. Identifying and
acknowledging the existence of this sub-group of laminitic cases will
prevent future cases of laminitis being caused in this way. Identifying these cases is difficult and relies
on the normal causes of laminitis being absent, particularly obesity or
other systemic diseases.
The presence of signs of treatment for a flexural deformity in the form
of desmotomy scars or a history of previously upright conformation helps
conform that heel lowering may have caused laminitis. Another helpful
diagnostic factor is the complete absence of any evidence of laminitis
in the hind feet, which will be perfectly normal. |
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Fig 8 Foot Trimming
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Flexor tendon involvement in laminitis
Over the past decade the role of the deep
digital flexor tendon in laminitis has been questioned, with some
believing that it plays a major part while others have disagreed,
perhaps both camps are correct. In ‘heel lowering induced laminitis’ the
deep digital flexor tendon will have a major causal role, while in the
systemically induced cases it will not have influenced the situation at
all.
Unfortunately, there are exceptions to all rules, a horse with
naturally upright conformation can still have systemic laminitis!
In my experience laminitis caused by heel
lowering is very difficult to deal with. My efforts have concentrated on
not lowering the heels but to allow them to grow longer or to raise the
heels with some form of wedging, this measure does allow the heels to
become load bearing and reduce the loading on the deep digital flexor
tendon.
Prevention will always be better than cure. By
recognising that a particular horse has a naturally higher than normal
hoof angle and leaving it that way, we will be doing the horse a great
service. Very few problems are associated with upright conformation when
it is accepted for what it is. Inflicting preconceived standards of
conformation onto the non-standard horse will only inflict pain and
misery on the horse in the long term. Unilateral
laminitis should not be confused with
supporting leg laminitis, although they both affect only one foot
they are induced in different ways. |
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