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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