TENDON injuries need little
introduction and are a common
feature of the busy equine vet’s
diary.
Tendons begin to form in the
embryo from stem cells. As they
develop, they produce extracellular
matrix proteins, giving the tendon
both elasticity and the tensile strength
required to connect muscle to bone
and provide both the storing of energy
required to operate limbs
and resistance to
strain.
Histologically,
a healthy tendon
is composed of
parallel arrays of
Type I collagen, with small amounts of
other collagens, elastin, proteoglycans
and glycosaminoglycans contributing
to the overall structure.
The collagen molecules aggregate
to produce collagen fibrils bundles
which then form fibres, with
tendiocytes packed between them.
The proteoglycans are interwoven
with the collagen fibrils and interact
with the surface of the collagen fibrils via glycosaminoglycan side
chains, e.g. dermatan sulphate and
chondroitin sulphate demonstrating
that proteoglycans play an important
structural role.
Injury triggers a number of events that recruit cells and stimulate the
tenocyte population to synthesise
collagen and proteoglycans.
Appropriate stimuli such as mechanical
stress and strain encourage synthesis
and remodelling of the collagen fibres.
Injury to tendons sees both elasticity
and strength impaired after healing
because the collagen fibres are re-
formed haphazardly and often do not
regain the “ideal” architecture.
Poor vascular supply to tendons is
a significant factor in the speed of
healing and the tendency for scar tissue
to form.
Before reviewing treatment options
it is worth brie y covering the classic
symptoms, noting that problems
often lie in gradual tendonitis going
unnoticed, when early action could
prevent further deterioration:
- Heat and swelling
- Lameness – although some horses
will remain sound - Pain under palpation
- Swollen tendon sheath
Ultrasound scanning after initial diagnosis will reveal the extent of tendon damage and fibre disruption.
Depending on the extent of the
injury, initial treatment options (largely
irrespective of which tendon is injured)
will address reduction of inflammation
by means of cold treatment, combined
with NSAIDs.
Rehabilitation regime
Once the inflammation is stabilised,
a rehabilitation regime needs to be
decided upon, beginning with box rest
and hand walking which increases by a
few minutes each week.
Again a balance is required between
the owner’s desire for progress and risk
of re-injury. A schedule of ultrasound
scans is essential.
Beyond a controlled
schedule of rest and exercise, there are
numerous other treatments that are
used with varying degrees of success.
A recent development which takes
advantage of the natural response to
mechanical stress in promoting the
remodelling of the collagen fibres
is low intensity pulsed ultrasound
(LIPUS).
LIPUS is non-invasive and the horse
feels no sensation during the 20-minute
daily treatments. LIPUS signals
travel through skin into soft tissue to
stimulate a clear biological response
at the cellular level. It shortens the
inflammatory period, enhances
vascularisation, promotes collagen
synthesis and remodelling and overall promotes quality repair.
LIPUS signals cause cell surface molecules called integrins to change
protein conformation and cluster at
the cell membrane, which initiates
intracellular signal transduction. This
in turn up-regulates protein expression,
releasing factors that play a key role in
tendon repair including IGF-1, PGE2,
COX-2, VEGF, PDGF, bFGF, TGFβ
and BMP-12.
