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The Farrier's Role in the Inferior Check Ligament Surgery
Stephen E. O'Grady, DVM, MRCVS
Overview
Inferior check ligament desmotomy has become a popular and
routine surgical procedure. Besides being used to treat
flexural deformities that result in club feet, it is used to
treat chronic laminitis and caudal heel syndrome. Yet with the
increasing use of this procedure, little has been written with
regard to the role the farrier plays in the pre- and
post-surgical care of the feet. In many instances, the
successful outcome of the case with regard to future function,
soundness and gross appearance of the foot are dependent on
the skills of the farrier.
Anatomy
The muscular part of the deep digital flexor tendon lies
directly on the caudal aspect of the forearm. A tendon is
formed from the muscle belly just before it enters the carpal
canal (behind the knee), the tendon continues down the palmer
aspect of the limb and inserts on the palmer surface of the
third phalanx (coffin bone). A strong tendonous band that
originates from the deep palmer carpal ligament joins the deep
flexor tendon at the middle of the metacarpus (cannon bone).
This is the inferior check ligament. The inferior check
ligament along with the suspensory apparatus of the fetlock
act as a stay apparatus to minimize overextension of the
fetlock during weight bearing. The deep digital flexor tendon
and the inferior check ligament can be considered one
muscular-tendonous unit. Any shortening of this structure from
various disease processes will cause a misaligned hoof pastern
axis and a deformity of the hoof capsule (usually a "club"
foot). Lengthening of the muscular-tendonous unit by resecting
the check ligament in turn will allow realignment of the hoof
pastern axis and changes to be made in the shape of the hoof
capsule.
Causes
Flexure deformities of the distal interphalangeal joint have
been traditionally referred to as "contracted tendons." As
discussed above, the primary defect is a shortening of the
muscluo-tendonous unit rather than just the tendon portion,
making flexure deformity the preferred term. In foals up to
the age of weaning, acquired flexure deformities are thought
to be associated with poor nutritional management (increased
protein, unbalanced minerals, etc). It is this author's
opinion that this syndrome is not part of the developmental
orthopedic disease (DOD) but a response to some form of pain.
Any discomfort in the foot or lower limb will initiate the
flexural withdrawal reflex which causes flexor muscle
contraction and altered position of the distal interphalangeal
joint.
The inferior check ligament desmotomy is used as frequently in
adult horses as it is used in foals. When an adult horse is
presented with a club foot, it is usually the result of a
condition that was unnoticed or left untreated when the animal
was a foal and the condition worsened due to the rigors of
training. It can also result from a disease process such as a
deep puncture wound, P3 fracture or any condition where the
normal physiology of the foot is not utilized through full
weight bearing.
Horses that are diagnosed with caudal heel syndrome which are
unresponsive to conservative therapy (therapeutic shoeing and
medication) often benefit from this surgery. These horses may
have a broken forward or broken back pastern axis and in
either case, the discomfort may be the result of the increased
tension on the deep digital flexor tendon as it passes under
the navicular bone in the heel area. Increasing the length of
the musculo-tendonous unit by resecting the check ligament may
decrease this tension and allow some shoeing options.
Diagnosis
The gross appearance of the foot will depend on the severity
of the flexure deformity and the length of time the condition
has been present. The foot will be characterized by unequal
horn growth, with excessive growth seen at the heels. With
this abnormal heel growth and the increased tension of the
deep digital flexor tendon,, the angle of the foot becomes
steeper with the coronary band protruding forward over the
face of the dorsal hoof wall. This abnormal position of the
third phalanx causes mechanical rotation to take place,
leading to a flat, thin sole and a "dish" appears in the
dorsal hoof wall due to the bending of the horn tubules. In
the young horse without shoes, full weight-bearing is placed
on the toe area, leading to damaged hoof wall (toe cracks),
fissures in the "white" line, bruising and abscesses. Chronic
lameness is often evident. In the adult horse, the altered
position of the third phalanx and the decreased sole depth
invariably lead to chronic foot bruising resulting in
lameness. Alternatively, it may be observed as a shortened
stride on the affected side. If lameness is present, it should
be localized to the affected foot using local anesthesia.
Radiographs are taken in all cases to assess the position of
the third phalanx (coffin bone), the sole depth that is
present and any damage to the perimeter of the coffin bone
(pedal osteitis). The x-rays are also used as a guide when
trimming the foot.
Pre-operative Treatment
As we use this procedure more frequently on adult horses, we
have developed a routine that has given us very good results
in returning the affected foot to a near-normal conformation
with a more pleasing cosmetic appearance at the surgery site.
All horses are trimmed and/or shod before the surgery so that
the operated limb does not have to be handled
post-operatively, the bandage is not distorted and the horse
can be hand walked immediately. With regard to the animal with
a flexure deformity or "club" foot, the emphasis of the
trimming is placed on lowering the heel area, beginning at the
heel and working toward the apex of the frog or widest part of
the foot in a tapered manner. The toe is shortened by removing
hoof wall from the dorsal surface, trying to remove as much of
the dish as possible. The toe area on the ground surface of
the foot in front of the apex of the frog is left untouched.
The radiographs are always used for guidance when trimming
club feet. This method of trimming is continued on the
subsequent resets in order to increase the sole depth,
maintain the alignment of P3 and promote normal physiology
within the hoof. It is our opinion that the gross normal
appearance of the hoof capsule is attained during the
post-operative period. The horse is shod with a toe extension
in all cases to force the heel down and delay breakover,
causing the flexor tendon to stretch just before breakover
(Fig. 3). The toe extension appears to prevent premature
re-attachment of the severed ends of the check ligament. We
also feel that the toe extension allows the coronary band to
assume a more normal position. The extension should extend
one-half to three-quarter inch beyond the toe of the hoof wall
depending on the size of the horse. The shoe is fit full at
the heels and allowed to extend beyond the end of the heel to
compensate for the extension. As much heel as possible should
be removed in order to restore a normal hoof angle. If the
horse shows discomfort following lowering the heels, a 4o
wedge pad is taped to the shoe prior to surgery and is removed
on the second or third day of post-operative walking.
In the case of the young horse (foal), a toe extension is
fabricated and bonded to the dorsal hoof wall using a methyl
methacrylate substance. Because of the damage to the toe area
and the subsequent pain, the sole area to the apex of the frog
is covered with a layer of fiberglass impregnated with a
methyl methacrylate substance1. When the foot is prepared for
application of the toe extension, a bead of modeling clay is
placed over the fissures on the white line and a layer of
impregnated fiberglass from the toe extension extends from the
dorsal hoof wall covering the sole to the apex of the frog.
This protects the damaged toe area, relieves discomfort and
decreases the need for phenylbutazone. The foal will walk
sound following surgery.
Horses that have been diagnosed with caudal heel syndrome and
have been unresponsive to conservative therapy are trimmed and
shod in such a manner that emphasis is placed on realigning
the hoof-pastern angle. The radiographs can be used to assess
anterior/posterior and medial/lateral imbalance. The heels are
moved back to the widest part of the frog and breakover is
improved by shortening the toe from the dorsal wall
accordingly. A wide web steel shoe is used for support. If the
heels are contracted, one can consider a steel shoe with
"beveled" heels.
Post-operative Treatment
Aftercare following the surgery consists of twenty minutes of
hand walking daily for the first ten days. After ten days,
hand walking is increased to twenty minutes twice daily for
three more weeks. A pressure bandage is kept on the operated
limb for sixty days. At one month, the horse is reset. The
foot is trimmed as described above and the toe extension is
removed. The horse is then turned out in a round pen or small
paddock for the next month. The horse can then be turned out
in the pasture. The horse is reset at four week intervals and
returned to work four to six months after the surgery.
Discussion
In cases of flexural deformity of the distal interphalangeal
(coffin) joint, there is a functional shortening of the deep
digital flexor musculo-tendonous unit. This shortening is
responsible for the abnormal changes that occur in the foot.
The increased tension of the flexor tendon causes the coffin
joint to be constantly flexed, which changes the angulation of
the third phalanx and increased weight bearing on the tip of
the bone instead of the entire solar surface. This abnormal
weight bearing leads to chronic foot bruising and lameness.
Until recently, the treatment of choice was to lower the heels
and apply a toe extension. This did little to change the shape
of the foot and the increased tension on the already shortened
tendon structure exerted most of its effect on the lamina,
leading to further mechanical rotation. The check ligament
surgery coupled with therapeutic trimming appears to be the
treatment of choice in the older animal. The inferior check
ligament desmotomy creates a lengthening of the deep flexor
tendon allowing the heels to be lowered. This brings the
hoof-pastern axis into normal alignment and allows the
necessary changes to be made within the hoof capsule. In all
the recent studies, it has been shown that check ligament
desmotomy does not affect future performance.
References:
Stick JA, Nickels FA, Williams MA. Long term effects of
desmotomy of the accessory ligament of the deep digital flexor
muscle in standardbreds: 23 cases (1979-1989). J Am Vet Med
Accoc. 1992; 199: 1131-1132.
Turner TA. Inferior check desmotomy as a treatment for caudal
hoof lameness. Proceedings, 38th Ann Conv Am Assoc Equine
Practn. 1992; 157-163.
Wagner PC. Flexural deformity of the distal interphalangeal
joint. In: White NA, More JN, eds. Cur Prac Eq Surgery.
Philadelphia: JP Lippincott, 1990; 472-475. |
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