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AUTUMN 2012 ISSUE
EQUINE MATTERS
8
SUSPENSORY LIGAMENT
Ultrasound scans showing fibre disruption in
the proximal suspensory ligament
Desmitis of the branches of
the suspensory ligament
These can also feel warm and swollen if
damaged. Again, lameness is not always
present so it is worth investigating any
swellings around the back of the cannon/
fetlock region. Horses are more likely to
strain the branches if the foot is not
correctly balanced. All types of horses can
be affected.
Unfortunately, re-injury is also common if the
branches are severely damaged.
Proximal suspensory
desmitis (PSD)
The origin of the suspensory ligament is
put under strain particularly in sports
horses which are required to engage
their hindquarters, and especially in
those that are trained on soft surfaces.
Microscopic damage to the collagen
fibrils builds up over time and causes
long-term (chronic) changes in the
ligament. Lameness can then gradually
develop (often initially seen as poor
performance) or may suddenly occur as
a result of an acute tear of the ligament
in an already weakened area.
Sometimes a small piece of bone can
be pulled (avulsed) off the back of the
cannon bone, which can be detected
on x-ray.
The prognosis for horses to return to full
soundness is better in the forelimbs than
the hindlimbs. Unfortunately, many of the
chronic injuries do not fully heal or recur
when exercise restarts.
Straight hock and low fetlock conformation
associated with a weakened suspensory
ligament in an older horse
Breakdown of the
suspensory ligament
in older horses:
The collagen in ligaments and tendons
becomes weaker with age. In geriatric
horses, the suspensory ligament
gradually stretches and becomes less
elastic, especially in the hindlimb. The
fetlock has less support so moves lower
towards the ground. This can be painful
and the horse may shift weight from
foot to foot more often than is normal.
Anti-inflammatories can be used long
term in these cases. Unfortunately, the
suspensory ligament can break down
completely in very severe cases
and euthanasia may be the most
humane option.
Usually, a combination of clinical
examination and further tests are needed
to make an accurate diagnosis. A flexion
test will often worsen the lameness if PSD
is present. Nerve blocks, using local
anaesthetic to desensitise the nerve
serving the suspensory ligament, can
be instrumental in localising the source
of the lameness.
Ultrasound scans can show a variety
of changes in the suspensory ligament
and shorter ligaments at the back of the
pastern, including enlargement, focal
damage or widespread degeneration.
X-rays are used to check for damage
to the cannon bone, splint bones or
sesamoid bones. Occasionally, a bone
scan (nuclear scintigraphy) is required
to make a diagnosis.
Diagnosis
Where an acute (short-term) injury is
present, anti-inflammatory therapy is useful
to reduce the ongoing damage to the
ligament. This can include bandaging,
cold hosing, ice packs and in-feed
anti-inflammatories such as bute. Box rest
is essential at this stage.
With chronic injury, treatment is usually
based around rest and controlled
exercise. Free exercise is often not
permitted in order to give the ligament a
chance to heal without being re-strained.
Some exercise can help, though, as it
encourages the new collagen fibres to
align themselves in an ordered
longitudinal formation. The repaired
ligament will not be as strong as the
original ligament, and may never look
normal on ultrasound scan. The ligament
is likely to take several months to heal,
perhaps up to one year or even longer
in rare cases.
PSD can be particularly difficult to
treat, especially in the hindlimbs.
Extracorporeal shock wave therapy can
help to reduce the local inflammation
and improve the long term prognosis.
A few cases may be suitable for surgical
treatment if other methods fail. Even if a
horse does not recover well enough to
return to its original use, it may manage
to work at a lower performance level.
Good farriery will help to maintain
correct foot balance and appropriate
shoeing will provide some support to the
function of the suspensory ligament.
Treatment
Suspensory body desmitis
The central part of the suspensory ligament is
most commonly injured in thoroughbred and
standardbred racehorses, but pleasure horses
can also be affected. It is important to be
vigilant when checking for swellings in the limbs
after exercise as often lameness may be mild or
absent in these cases. Heat and swelling can
be felt mid-cannon region in front of the main
flexor tendons. Sometimes the splint bones can
be damaged by the swollen ligament so x-rays
are often taken to check for this.
Usually the ligament will heal but re-injury
can occur.