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AAEP Mission
Statement:
To improve
the health and welfare of the horse, to further the professional
development of its members, and to provide resources and leadership
for the benefit of the equine industry.
~ American
Association of Equine Practitioners, Online
The coffin bone is the primary bone within the horse's foot. The
hoof capsule encases this bone like a body in a coffin (hence the
name coffin bone). The laminae within the foot are the soft tissue
structures that firmly attach the coffin bone to the hoof wall.
Laminitis, in its simplest terms, is inflammation of the laminae
that attach the coffin bone to the hoof capsule. This inflammation
decreases blood flow to the area of the laminar attachments. Local
alterations in blood flow may be the result of a variety of systemic
illnesses, such as grain overload, colic, retained placenta, etc.
Whatever the source of the disease, laminitis usually causes crippling
pain in horses and is potentially devastating to horse owners.
In some instances, the laminar attachments become so compromised
that the coffin bone and hoof capsule actually separate from each
other. If the normal pull of the deep digital flexor tendon exceeds
the strength of the remaining laminar attachments, the bone may
rotate downward away from the hoof wall. Veterinarians consider
the disease chronic if rotation occurs or if the condition lasts
for more than several days.
Most treatments for laminitis focus on improving blood flow to
the foot, alleviating the pain associated with this condition,
halting disease progression, and re-establishing a functional relationship
between the coffin bone and hoof wall. Veterinarians often use
vaso-dilating agents such as acepromazine, isoxsuprine, pentoxyphyline,
and nitroglycerin in hopes of improving blood flow. Phenylbutazone
(Bute) commonly relieves pain and decreases inflammation in laminitic
horses. A variety of recommended shoeing and trimming techniques
attempts to decrease the amount of tension on the coffin bone and
redistribute pressure on the hoof's weight-bearing surfaces.
In spite of extensive research, numerous approaches to treating
horses with laminitis are sometimes frustrating and unrewarding.
A multi-factorial condition, laminitis involves several body systems
and prevents a single treatment regimen from becoming universally
accepted or effective. When the disease does not respond favorably
to conventional therapies, owners often turn to euthanasia to end
the intractable pain of this condition.
The purpose of the authors' current study, presented at the AAEP's
44th annual meeting in Baltimore, Md., was to evaluate a surgical
option for laminitic horses that failed to respond to standard
treatments. Deep digital flexor tenotomy is a surgical alternative
that transects the deep digital flexor tendon in the mid-cannon
bone region. This major tendon runs down the back of the horse's
leg and attaches to the back of the coffin bone. Transection removes
one of the main forces responsible for rotation of the coffin bone
in laminitis. This surgery may also alleviate a source of pain
by decreasing pull on the bone and inflamed laminae. Under local
anesthesia, the horse stands during this quick and minimally complicated
procedure.
This retrospective study evaluated the procedure's effectiveness
by obtaining follow-up information on all horses with laminitis
treated by deep digital flexor tenotomy over a 10-year or more
period. Thirty-seven cases met the criteria for inclusion in the
study. Seventy-seven percent of the horses that had the operation
were still alive after six months, and 60% survived at least two
years. The results are substantial, considering the severity of
the laminitis and extreme lameness of all the study horses prior
to surgery. These horses had not responded to established medical
treatments and many were facing euthanasia. The high percentage
of owner satisfaction with the surgery seems to indicate the improved
quality of life for these horses. Seventy-three percent of owners
said they would have the procedure repeated in similar circumstances,
17% would not, and 10% were unsure. The study also found that the
severity of lameness and amount of rotation evident on pre-surgical
X-rays did not influence the outcome of the operation.
Previous studies have yielded conflicting results for the procedure.
Some indicate the procedure is less effective early in the disease's
process during the acute stages of laminitis. Others show a lack
of response to any kind of treatment in cases where the coffin
bone sinks in the hoof capsule rather than rotating. When the bone
sinks, the extensive loss of laminar attachments contributes to
the disease's severity.
Horse owners should consider the cost of aftercare when contemplating
tenotomy of the deep digital flexor. The actual operation is relatively
inexpensive because the surgery does not require general anesthesia.
Expenses accumulate from the essential corrective trimming and
shoeing performed by a qualified farrier at four-week intervals.
In rare instances, the horse's toe will flip up following tendon
transection due to the loss of the supporting structure. This condition
necessitates a heel extension on the affected foot.
The severed tendon heals with scar tissue, leaving an enlarged
thickening on the leg where the tissue forms. Some horses may become
sound enough to resume light work, but most achieve pasture soundness
and are best suited for breeding purposes. Although a universally
effective treatment for laminitis is unlikely, tenotomy of the
deep digital flexor tendon may benefit selected horses with chronic
laminitis which continues to deteriorate despite intensive medical
therapy.
Timothy G. Eastman, DVM, MPVM, and
Clifford M. Honnas, DVM, Diplomate ACV |
