Introduction:

Inferior check ligament desmotomy is frequently performed on foals (ages 2-8 months) for flexural deformity involving the distal interphalangeal joint (1). There are very few reports in the literature of this procedure being performed on adult horses (2), but some reports indicate that poor results are achieved in adults (3,4). Flexural deformity, when seen in the young racing thoroughbred, can lead to chronic intermittent lameness resulting in poor performance. This deformity may be the result of the animal not being treated successfully as a foal and the condition worsening due to the rigors of training. Flexural deformity may also be acquired secondary to chronic excessive trimming of a steeply angled hoof in an attempt to balance the feet. If the flexural deformity is severe, it can lead to unilateral laminitis secondary to constant trauma to the lamina of the toe area, resulting in marked rotation of the third phalanx. Unilateral laminitis could also be present secondary to other etiologies. In all cases, the affected foot shows an increased hoof angle (> 60 degrees), a broken forward hoof -pastern axis, a prominent coronary band and a long heel with a relatively short toe, i.e. a club foot. Pain is thought to result from the increased angulation of the third phalanx and the thin flattened sole which leads to chronic foot bruising.

The purpose of this paper is to describe the use of inferior check ligament desmotomy as a successful treatment of flexural deformities (11 cases) and, coupled with additional therapy, as a treatment for unilateral chronic laminitis (4 cases) in adult horses. This paper also outlines the need for a close working relationship with a farrier for a successful outcome to these cases

Materials and Methods:.

Fifteen horses 2 years old or older had inferior check ligament desmotomy performed as a treatment for flexural deformity (11 horses) or chronic unilateral laminitis (4 horses). The differential diagnosis of a flexural deformity or chronic laminitis was determined from the history, radiographic evaluation and the gross appearance of the solar surface of the foot.

All horses included in this study had a history of low grade lameness and poor performance, especially when training was intensified. When presented, all horses showed a shortness of stride on the affected limb when trotted in a straight line and a grade II (I-V) lameness when trotted in a tight circle with the affected limb on the inside. The affected foot showed a steep angle, the hoof pastern axis was broken forward, there was a bending of the horn tubules in the anterior hoof wall ("dish") and the sole was flat. The consistency of the hoof wall in the region of the toe was poor. Hoof testers revealed discomfort when applied to the solar area of the toe. Intra-articular anesthesia of the distal interphalangeal (DIP) joint did not improve the lameness. Posterior digital nerve block improved but did not eliminate the lameness. Abaxial nerve block eliminated the lameness in all cases, thereby localizing the discomfort to the dorsal portion of the foot. Radiographs of both the normal and affected foot were taken in all cases and were used to determine radiographic changes in the DIP joint, the coffin bone, the amount of sole depth present and the position of the third phalanx within the hoof capsule. Horses that were judged to have marked rotation of the third phalanx (>10 degree rotation) and minimal or no sole depth were diagnosed with laminitis (5). Prior to surgery, the affected foot was trimmed using the radiographs as a guide in order to realign the third phalanx. The horse was then shod with an egg bar shoe with a three quarter inch toe extension.

In the cases with chronic laminitis, the heel area of the affected foot was also trimmed according to the radiographs. In order to increase the sole depth, the affected foot was elevated 16 degrees by attaching a stack of wedge pads. The horse was confined to a stall four to six weeks until the sole depth reached 1 cm as determined by serial radiographs (6) The wedges were then removed, the heel was trimmed as necessary, the horse was shod as described previously and three wedges (12 degrees total) were taped to the shoe prior to surgery.

All horses were placed under general anesthesia in lateral recumbency with the affected limb up. The surgery was performed as described elsewhere(2) with a few variations. Aftercare consisted of twenty minutes of hand walking daily for the first ten days. Anti-inflammatory agents were used during this time. Bandage changes were done only as necessary and bandages were maintained for six weeks post operatively. After ten days, sutures were removed and walking was increased to twice daily for the next two weeks. The toe extension was then removed and the horse was turned out in a small paddock. The horseshoes were reset at three week intervals. Horses returned to training in 90 days.

Chronic laminitis cases were walked immediately following surgery with the wedge pads taped to the shoe. The wedges were removed gradually, one at a time, during the first ten days. The remainder of the convalescent period was identical to that outlined previously except that these horses were given an additional month of turn-out before training was resumed.

Results:

Seventeen inferior check ligament desmotomies were performed on fifteen horses (Table 1, below). The median age of the horses was three years. Eleven horses were thoroughbreds and four were Hanovarians. One horse died of colic post-operatively. All horses were examined monthly for six months; thereafter, long-term follow-up was through telephone communication with the trainer.

Success in this study was defined using three criteria. Firstly, all survivors became sound and resumed training. Secondly, over 50% of the horses improved in performance (won or placed in races or shows) and the remainder of the horses continued in training with no subsequent lameness. Thirdly, the surgery and farrier care allowed the third phalanx to be realigned within the hoof capsule and the gross appearance of the affected hoof improved to within 75% of the normal foot. The cosmetic appearance of the operated leg was acceptable with a small fibrous thickening present.

Discussion:

In cases of flexural deformity of the DIP joint, there is a functional shortening of the deep digital flexor musculo-tendonous unit. This shortening is responsible for the abnormal changes that occur within the foot. The increased tension of the flexor tendon causes the DIP joint to be constantly flexed, which causes a change in angulation of the third phalanx and increased weight bearing on the apex of the bone instead of the entire solar surface. This abnormal weight bearing leads to chronic foot bruising and lameness. All flexural deformities appear to have some radiographic signs of rotation but this may be due in part to the distortion of the hoof capsule, the bending of the horn tubules of the anterior hoof wall and the flat thin sole resulting from the increased pressure on the apex of the third phalanx. Various forms of corrective trimming and shoeing have been used to correct this deformity but in the authors' experience they have not been as successful in the older animal. The check ligament surgery coupled with therapeutic trimming appears to be the treatment of choice in the older animal. Inferior check ligament desmotomy creates a lengthening of the deep flexor tendon allowing the hoof angle to be lowered. This brings the hoof-pastern axis into normal alignment and allows the necessary changes to be made within the hoof capsule.

We believe that the farrier input in this study was as important as the surgery. The feet were trimmed and shod before surgery so that the operated limb did not have to be handled post operatively, the bandage was not distorted and the horse could be hand-walked immediately. The foot was trimmed using the radiographs for guidance. The emphasis of the trimming was placed on lowering the heel area, beginning at the apex of the frog or the widest section of the foot palmed to the heel. The toe was shortened by removing the 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 was left untouched. This method of trimming was continued on the subsequent resets. It is our opinion that the gross normal appearance of the hoof capsule is attained during the post operative period. A toe extension was used on all cases to force the heel down and delay breakover, causing the flexor tendon to stretch just before breakover. This appears to prevent premature reattachment of the severed ends of the check ligament. An egg bar shoe, extending beyond the heels was used in all cases. If the flexural deformity is severe, the angulation of the third phalanx will cause disruption of the lamina leading to marked rotation. The rotation causes these horses to have minimal or no sole depth. Various methods of corrective shoeing revolving around frog support have been employed for chronic laminitis with inconsistent results (7). One problem often encountered with shoeing laminitic horses is the re-establishment of a normal sole depth with a good consistency. Elevating the heels 16 degrees prior to surgery decreases tension on the deep flexor tendon allowing the re-establishment of a normal sole depth. The surgery, through functional lengthening of the musculo-tendonous unit, then allows the third phalanx to be realigned within the hoof capsule. With the heels being elevated prior to surgery, it was believed that there could be additional shortening of the flexor tendon, this being the reason the foot was again elevated prior to surgery and the wedge pads removed gradually afterwards. It also gave a clear indication of the ability of the musculo-tendonous unit to stretch following surgery.

Controversy surrounds the long term athletic performance of adult horses following inferior check ligament desmotomy. The horses in this study, although a small population, have remained sound, their level of performance has increased and they have withstood the rigors of training and jumping. These data therefore demonstrate the benefit of inferior check ligament desmotomy to treat flexural deformity and chronic laminitis in the adult horse. It has also been shown that, through corrective trimming, the hoof angle can be permanently changed restoring a more normal anatomic and physiologic function. Finally, we were encouraged by the combined therapy in the laminitic horses which gave us consistent results in a limited number of cases.

Stephen E. O'Grady, DVM, MRCVS

Dr. Stephen E. O'Grady is an equine practitioner and farrier practicing in the Northern Virginia area. He operates the Northern Virginia Equine Podiatry Center near Middleburg Virginia. He is also a member of the Farrier's Liaison Committee of the American Association of Equine Practitioners.
 

References:

1. Wagner PC. Flexural deformity of the distal interphalangeal joint. In: White NA, Moore JN, eds. Cur Prac Eq Surgery. Philadelphia: JP Lippincott, 1990; 472-475.

2. Turner TA. Inferior Check Desmotomy as a treatment for caudal hoof lameness. Proceedings, 38th Ann Conv Am Assoc Equine Practn 1992; 157-163.

3. 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 Assoc1992; 199:1131-1132.

4. White NA. Inferior check ligament desmotomy using ultrasonic guidance. Vet Surg1991; 20:351.

5. Stick JA, Jann HW, Scott EA, et al. Pedal bone rotation as a prognostic sign in laminitis in horses. J Am Vet Med Assoc 1982; 180:251-253.

6. O'Grady SE. A practical approach to treating laminitis. Vet Med 1993; 88:867-875.

7. Moyer W, Redden RF. Chronic and severe laminitis: a critique of therapy with heart bar shoes. Eq Vet J 1989; 21(5):317-318.