Bowed Tendon
When people say a horse is "bowed", or that it has a
"bowed tendon", they are generally referring to tearing of the
superficial digital flexor tendon in the middle of the cannon bone
region. This tear causes a curved, bow-like swelling on the back of the
leg between the knee and the ankle.
Although the swelling is usually in the middle of the cannon bone, it
may be behind the knee, at the level of the ankle, or it may extend from
the knee to the pastern. Most people think tendon injuries such as
"bowed tendons" only happen to racehorses. In reality, any breed or type
of horse, performing almost any activity, can be at risk for tendon
injury. Tendon injuries can be more serious than some types of fractures
because the tendon heals very slowly and replaces torn tendon fibres
with fibrous scar tissue. The healed tendon is less elastic, leaving the
tendon vulnerable to re-injury. When there is a significant injury, the
horse may not be able to return to its previous level of performance due
to persistent weakness of the tendon.
The superficial digital flexor tendon is made of protein fibres that are
arranged longitudinally, forming a long attachment between the muscle
above the knee, and the long and short pastern bones just above the
hoof. The tendon fibres are somewhat elastic, but will tear if stretched
or loaded beyond their limits. Improper positioning of the leg in
relation to the horse's body weight can tear the tendon fibres. This
configuration may occur when the horse lands after a fence or as the
horse becomes tired and changes its gait. Any unbalanced loading of the
tendon, uneven footing, poor conformation, and/or improper shoeing can
also contribute to tendon damage. In some cases this overload can be the
result of a single misstep, and in other cases it can be the result of
cumulative stress or fatigue of the fibres.
Once the tendon fibres tear, bleeding within the tendon causes acute
swelling, heat, and pain. The horse may or may not exhibit lameness. In
fact, many horses with serious tendon damage are never lame. Swelling
also occurs around the tendon due to an accumulation of fluid (oedema).
In the short term, ice or cold hosing and bandaging the leg should
decrease the local inflammation and swelling. The horse should be
confined to its stall with only hand walking exercise. If the horse is
sore or significant swelling is present, consider speaking to a
veterinarian about using oral phenylbutazone for a short period of time
to decrease the swelling and discomfort. Since palpation of the leg is
not a reliable method of determining the presence of tendon damage,
contact a veterinarian to make arrangements for an ultrasonographic
evaluation of the swelling.
Ultrasonography allows a veterinarian to evaluate the integrity of the
tendon fibres as well as other important parameters, including the
cross-sectional area of the tendon, the alignment of its fibres, and its
echogenicity. The echogenicity of the tendon is related to its density.
The\ normal tendon appears bright white or echogenic, and the abnormal
tendon appears various shades of grey (hypoechoic) or black (anechoic).
Based on the ultrasonographic findings, a veterinarian can confirm the
presence of tendon damage and determine its severity. Subtle tendon
damage may display an increase in the tendon cross-sectional area due to
oedema, without actual fibber tearing. Serious damage may consist of
total tendon rupture with complete loss of the tendon fibres, a marked
increase in tendon cross-sectional area, and loss of support in the
limb. Most tendon injuries fall somewhere in between with a discrete
area of fibber tearing visible on the ultrasound image (black or dark
grey hole), and enlargement of the total tendon cross-sectional area.
The hole seen on the ultrasound is actually an accumulation of blood and
granulation tissue within the tendon where the tendon fibres have torn
apart.
If your horse has suffered a tendon injury, a veterinarian will work
with you to develop a rehabilitation plan. Most horses need stall rest
with restricted exercise for at least two months (possibly up to eight
months), depending on the degree of injury and the horse's temperament.
This confinement, coupled with a controlled exercise program, will
encourage healing of the tendon while preventing re-injury. Initially,
the horse should only be walked in hand. Once the tendon has been cooled
out, cold hosing is no longer necessary or helpful. Topical application
of DMSO may help decrease residual swelling in the leg, but the tendon
will remain persistently thickened in the majority of cases.
A veterinarian will need to ultrasound the horse's leg approximately
every sixty days after the initial exam to determine if the tendon has
healed enough to allow for an increase in exercise. An increase in
exercise may entail up to five minutes of jogging exercise or turnout in
a small paddock. This exercise will gradually increase over a period of
months; depending on the improvements seen during the follow-up
ultrasound exams. Tendon rehabilitation is a slow process that can be
frustrating if your horse suffers any setbacks due to re-injury.
Monitoring the horse's progress with regular ultrasounds can eliminate
these setbacks.
Recent research in veterinary medicine has focused on ways of improving
the outcome of tendon injuries. Surgical treatments that include tendon
splitting and superior check ligament desmotomy have been found useful.
Physical therapy modalities such as therapeutic ultrasound, low-power
laser, and magnets are also thought to promote tendon healing. In some
cases, the use of intralesional medication, such as BAPTEN(R), may be
beneficial in improving the quality of tendon repair. In the future,
veterinarians may use biodegradable artificial tendons as scaffolding
for tendon reconstruction. A veterinarian can help choose the best
treatment for each individual horse.
Although tendon injuries are serious, most horses can recover and return
to athletic function if given enough time. Even in the case of a severe
tear, it is likely that a horse will be able to return to a less
strenuous activity. The best way to ensure a successful outcome is
through prompt ultrasonographic diagnosis, treatment, and careful
monitoring of the tendon by a veterinarian.
Extracorporeal Shock Wave Therapy (ESWT)
This is the most promising treatment option for bowed
tendons to come along in decades.
Bowed tendons are a major cause of wastage in the industry, because the
lay off required for complete healing resolution is very long. While the
treatment options previously mentioned in this article have been touted
as effective, the sceptical brigade maintain that it is the long lay off
period itself, more than any kind of therapy, that really ever heals
bowed tendons.
ESWT appears to have the potential to turn this situation around and
offer a realistic alternative to the cost of long spelling/rehab
periods.
ESWT involves the use of very high frequency sound waves focused into
the injured tissue by means of a special probe (similar to an ultrasound
probe), to stimulate the cells themselves into a mode of high level
production of healing compounds. High frequency sound waves travelling
through tissue behave somewhat like a physical wave on a cellular level,
and as such, deform and stretch the cell membranes. This then creates a
massive stimulus to the biochemical internal cell mechanisms that
produce healing factors. It could be likened to giving the cells
themselves an individual physical massage (or rather, pummelling) to
kick start the healing process. The final effect is not unlike an
internal blister, where the inflammation is resolved rapidly into scar
tissue.
The cells of the tendons are notoriously slow in their ability to heal,
and it is this phenomenon that necessitates such a long lay off period.
However, with the exciting new technology offered by ESWT, the
veterinary profession at long last has a tool, that is non-invasive and
easily applied, to stimulate the sluggish metabolism of the tendon cells
(and also cells of bone and suspensory ligaments) and dramatically speed
up the healing resolution of such injuries.
For example, recently in Asia, some horses with bowed tendons were
treated with ESWT.
Black holes on the ultrasound scan that would normally take 6-12 months
to fill in were fully healed within 6 weeks and the horses were able to
return to active work.
Of course, any horse that returns to active work after a serious lower
leg injury such as a bowed tendon, has an increased risk of re-injuring
again, no matter how soon or how long that injury has taken to heal.
ESWT is a great new breakthrough in speeding the healing of tendon
injuries but it cannot create healed tissue that is beyond the strength
of normal. Therefore, all precautions should be taken with these horses
returning to active work to prevent re-injury; such as attention to
detail in shoeing, track surface and work regimes.
As this new therapy becomes better researched and understood around the
globe, the veterinary profession will be able to offer the horse
industry scientifically sound programmes to rapidly rehab these horses
and keep them performing.
Meanwhile, ESWT is an exciting new tool to salvage many horses with
injuries that would see them either retire, change careers or even lose
their life.