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Shin-soreness (dorsal metacarpal disease,
bucked shins, shin splints) is probably the most common cause of lameness in
young thoroughbreds. It is a major reason for interrupted training programs
and for preventing horses racing as two and three year olds.
Shin-soreness is characterised by pain over the dorsal (front) aspect of the
cannon bones, usually of the
forelimbs. As both limbs are usually affected the horse is often not overtly
lame in the early stages.
Work riders describe affected horses as feeling `scratchy' and `not
stretching out'. In more advanced cases the horse will become obviously lame
at a hand-led trot, as one leg is invariably more painful than the other.
Shin-soreness is part of a group of conditions caused by non-adaptive
exercise induced bone remodelling. It is caused by the cannon bone's
inability to adapt effectively to the stresses placed on its dorsal surface
as the speed and distance of training increase. All bone is constantly
undergoing metabolic changes; being resorbed and laid down in response to
the varying stresses associated with training and racing. The further young
horses gallop, the greater the stress on the front of the cannon bones,
leading to haemorrhage below the periosteum (the tough fibrous layer of
tissue which overlies the bone), microfractures, laying down of new bone on
the dorsal surface and, in more severe cases, stress fractures.
Signs of shin-soreness include heat over the front of the cannon bones and
pain on palpation. These signs are usually adequate to identify the problem,
but radiography or scintigraphy (bone-scanning) may be required to
definitively diagnose stress fractures.
There are many different factors which may contribute to the development of
shin-soreness. Bigger, heavier horses can be more prone to the condition, as
the forelimbs are carrying relatively more weight. The surfaces on which
horses are trained are a major factor. Hard and/or uneven tracks contribute
significantly to the problem.
Studies have shown
that horses trained on dirt are more likely to become shin-sore than those
trained on
wood-fibre and on well managed turf tracks. The financial incentives of
early two year old racing also contribute, by encouraging owners and
trainers to have their horses racing as early as possible. Horses with
poorer conformation may be more likely to develop shin-soreness along with a
number of other orthopaedic problems.
Treatment and management of shin-soreness varies from horse to horse. It is
important that horses are
examined thoroughly to rule out other causes of poor performance and
lameness, which often affect younger horses (eg foot, fetlock and knee
problems). Early cases may be successfully treated with topical and
systemic non-steroidal anti-inflammatory drugs, such as phenylbutazone, and
the application of ice or cold poultices.
There is evidence that shin-soreness can be minimised by reducing the
distance that young horses work
as the speed of that work increases. This allows the bone at the front of
the cannon to better adapt to the
stresses of higher speeds without causing the sub-periosteal haemorrhage and
associated inflammation and pain. Swimming is also a very useful part of the
management of shin-sore horses. It allows the development of cardiovascular
and muscular fitness without loading painful limbs.
Horses with mild shin-soreness in their first or second preparation may show
complete resolution without
recurrence with either a reduction in the amount of high speed exercise, or
just a short (six to eight week) paddock spell.
Many other treatments have been used over the years, including pinfiring
(now banned in Australian racing), application of blisters, local injection
of corticosteroids and systemic injection of growth hormone.
More recently extracorporeal shock wave therapy (ESWT) has been used to
treat and prevent shin-soreness.
The technique has been shown experimentally to increase bone turnover, as
well as having an analgesic effect. Thus ESWT may hasten the adaptive
changes required to cope with the rigours of training an racing. Whilst as
yet unproven ESWT may become a useful technique to reduce the number of
training days lost to shin-soreness.
More severe cases, which result in stress fracture, may require prolonged
periods of confinement followed by paddock rest, or surgery to stimulate
adequate healing.
The long-term prognosis for racing is generally good, however, horses will
often miss early racing opportunities as a result of repeated bouts of
shin-soreness. This can represent significant financial loss to the owner
who pays training fees, but is unable to see his or her horse race until
much later. |
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