Everything Horse magazine Everything Horse UK Magazine, November 2014 | Page 36

HEALTH: TENDON INJURIES

an introduction to the series
Pain due to musculoskeletal
injury is the most common
cause of performance loss in
horses. Most cases will initially
present as a behavioural
problem or a performance/
training issue, early diagnosis
and treatment will improve

the long term outcome. This
is the first in a new series of
articles by Michelle Woolrich,
animal musculoskeletal physical
therapist, looking into the
main types of muscloskeletal
injuries that can occur in our
horses; tendon injuries, muscle

injuries, bone injuries, and
ligament injuries. This will help
owners understand how this
type of injury occurs, how they
heal, how they are treated and
rehabilitated, and how they can
be avoided. This month begins
with tendon injuries.

Tendon Injuries

inflammatory stage, which lasts
approximately 48 hours. Inflammation is
always the first response to any damage
which needs to be limited and reduced.
Inflammatory products and debris cause
more tissue damage, fluid and swelling.
The longer inflammatory debris remains
in the area the more scar tissue will be
formed.

a stronger and stiffer tendon structure,
it is still vital to prevent overloading or
excessive stress on tendons. However,
controlled exercise is vital to improve tissue
fluid movement and to give controlled
stresses and tension to the new collagen
being laid down encouraging fibres to
realign along the lines of stress. However,
this collagen is of still of a weaker type.
Remodelling continues throughout
rehabilitation, replacing this weaker
collagen with a stronger type, but this may
take up to a year.

What are tendons?

Tendons are parallel, longitudinally
arranged bundles of dense, connective,
elastic, white tissue fibres, mainly
composed of collagen, that attach muscle
to bone and transmit forces from tendon
to bone. Tendons enable the limbs to
bear weight and move. Strength is found
from the collagen fibrils surrounded by
fibroblasts which form the basic tendon
bundle. These form secondary bundles
(fasciles) which form larger bundles in a
helical pattern. The strength comes from
this inter woven helical structure. These
are surrounded by loose connective
tissues, tenocytes (that produce collagen),
and blood vessels, but blood supply is poor.

Healing

Healing is slow due to the poor blood
supply and even with optimum healing,
new tendon tissue is not the same as the
original; there is less elasticity so a higher
chance of re-injury.
The first phase of healing is the

Tendon Injuries
Musculoskeletal
Injuries: Part 1

36

The Tendon injury
The mid portion of the superficial digital
flexor tendon (SDFT) of the forelimb is
the most commonly injured tendon in the
horse. As it has the smallest cross sectional
area, it is an area of natural weakness, and
has the least effective blood supply, which
may also cause progressive degenerative
lesions gradually over time through lack of
oxygen.

Damage occurs when the tendon bears
extreme stretching forces pushing it past its
“stress capacity” as a result of overextension
of the fetlock joint when weight is all
carried on one leg (e.g. when landing over
a fence). This causes over stretching of the
collagen fibres, and once it overcomes its
structural strength, there is disruption to

Everything Horse UK Magazine • Issue 14 • November 2014

Image credit Mike Bain

The next stage is the repair phase. Cells
migrate into the damaged area, new blood
vessels permeate the area pushing their
way through the swollen tissues carrying
cells to repair the tendon, laying down
collagen to form a scar and removing
damaged tissue. The repair collagen is not
naturally arranged longitudinally in the
same direction of pull as normal fibres,
which reduces its strength. Although
scar tissue itself is less stiff than tendon,
because large amounts are formed, it
results in a stiffer tendon than the original.
It is strong but functionally inferior, which
predisposes it to re-injury, often at sites
close to the original injury.
Finally, the remodelling phase. More fibres
are formed to replace the scar tissue with

Treatment and
rehabilitation

Treatment is initially aimed at decreasing
swelling, haemorrhage and inflammation
to minimise permanent damage, and
later, to guide the repair process. Antiinflammatory medications, the application
of cold, support bandaging, and rest is vital
to prevent further injury. At 48 hours to
3 weeks use heat therapy or hot and cold
therapy alternating to maximise blood
flow for repair. After this, treatments are
aimed at increasing the rate and quality
of repair, and minimising the rate of
recurrence by minimising adhesions and

the tendon matrix. This
varies in degree from fibre
slippage, to rupture and,
in severe cases, complete
separation of tendon tissue.
Most often, just a proportion
of fibres are damaged
resulting in a zone of
damaged fibres within the
body of the tendon forming
a “hole”, known as a core
lesion.
Extreme stretching forces
while the fetlock is extended with all the
weight is on one leg occurs as the horse
lands over fence. If it over

November 2014 • Issue 14 • Everything Horse UK Magazine

extends and the tendon is pushed past
its stretch capacity, damage will occur.
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