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Over time there have been significant advances in veterinary
science and in training methods for horses and ponies, but
tendon strains still represent a common injury - 43% of all
injuries that occur to event horses in training.
David Rutherford BVM&S CertES(Orth) DipECVS MRCVS
TENDON INJUR I ES
Tendon
Injuries
Until recently, strains were thought to be the
result of a single event where excess loading
was placed on the tendon - an abnormal
loading event - such as landing awkwardly
after a jump. However, we now know that
significant weakening occurs within a
tendon during normal training and prior
to visible injury. This weakening is called
‘microdamage' and occurs within a tendon
as a result of repetitive stretching during
normal exercise. We might expect that
natural healing would correct this
microdamage, and this probably does
occur to some extent, however due to the
very poor blood supply within tendons this
repair is often incomplete.
Fellowes Farm Equine Clinic Ltd
V E T E R I N A R Y S U R G E O N S
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Veterinary Surgeon
David Rutherford
XLEquine Practice
Fellowes Farm
Equine Clinic
What factors contribute to accumulation
of microdamage?
1)
Increasing miles on the clock
The more exercise a horse has done during
its lifetime, the more times their tendons
will have been stretched and as a result
the total amount of microdamage within
a tendon increases. The total amount
of exercise performed during a horse's
lifetime depends largely on their age
and how intensely they train and exercise.
Therefore an older horse who has trained
intensely will be at an increased risk of
tendon strain.
2)
Impaired ability to repair
Unfortunately as we get older our ability to
heal injuries naturally reduces. Therefore
older horses have reduced ability to
repair microdamage than their younger
counterparts. There are also some diseases
which reduce the body's natural ability to
heal, most notably Cushing's disease.
3)
Discipline
More microdamage occurs when tendons
are stretched to their limits or heated
beyond normal body temperature, as
happens during fast work or when landing
after a jump. Temperatures of up to 45°C
have been recorded within the tendons of
galloping horses causing significant thermal
damage. Therefore horses who regularly
gallop flat out are at increased risk, as are
those who jump. Eventers and National
Hunt racehorses are clearly therefore at
greatest risk of tendon injury and we
know that tendon strains do indeed occur
most commonly in these two groups, but
they are not alone. Horses undertaking
dressage training repeatedly perform
complex manoeuvres which put significant
pressures on their tendons, resulting
in accumulation of considerable
microdamage. Even 'happy hackers'
do not escape some risk.
4)
Increasing weight
This one is simple - the heavier the horse,
the more weight a tendon has to deal with
and therefore the more microdamage
occurs. This applies to both tall horses
and stockier horses.
5)
Genetics
Little is known about this, but it certainly
appears that some horses are genetically
predisposed to suffering tendon injuries.
This is likely to be because either they
inherently develop more microdamage
than their counterparts, or because they
are less able to naturally heal the damage.
This is an interesting area of current
research. In the future it may be possible to
genetically screen horses for their individual
risk of suffering a tendon injury, and
therefore selectively breed for horses with
a reduced risk. For the time being at least
we should question the wisdom of using
horses which have suffered tendon strains
for breeding.
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EQUINE MATTERS