Electric fence wire, barbed wire, sheet metal...What do these things have in common? They
all have caused catastrophic tendon injuries in horses. The structure and function of tendons, as well as flexor tendon desmitis, were reviewed in the July issue. In this article, we will focus on the therapy and prognosis for the laceration of a tendon. Obviously, given the structure and function of the main tendons of a horse's leg, any disruption of tendon integrity potentially can have a significant negative impact on a horse's athletic ability.

Several important points to remember are these:

  1. Should the flexor tendons become lacerated or transected under normal circumstances, the forces in a standing and weight-bearing horse would be enough to pull the wound apart (the degree of damage depends on how much tendon is involved).
  2. Damaged tendons heal with scar tissue that is not as strong or flexible as the original tendon, a fact that can greatly affect the future use of the horse.
  3. It is difficult to reduce the forces applied to the flexor tendons and often requires intervention beyond a simple leg wrap.

Evaluating The Injury

The first step in evaluating a tendon laceration is determining the structures involved and the degree to which they are involved. Location on the leg is important.

Remember the tendon sheaths? Lacerations involving the tendon sheaths can be of special concern and need to be noted. If the laceration is in the area of a joint, there always is concern. (For the purpose of this article, we will focus on lacerations involving only the tendons.) If the nature of the laceration is sharp, the evaluation often is easier as the structures involved are well-defined vs. lacerations associated with a dull cutting and/or tearing where little defined structure remains.

When the flexor tendons are injured, there are some characteristic alterations in limb posture that occur depending on what structures are affected. Working from superficial to deep, if only the skin is involved, consider yourself and your horse extremely lucky. If the superficial digital flexor tendon is only partially involved, there generally is no alteration to posture. However, if the superficial digital flexor tendon is completely transected, the fetlock has lost some of its support structure and the fetlock will "drop" some or become closer to the ground when compared to the normal leg. This drop can be subtle, since the main fetlock support structure is the suspensory ligament. The important indicator is that the foot remains flat on the ground if only the superficial digital flexor tendon is
transected.

When the deep digital flexor tendon is lacerated, the toe often will "pop up" off the ground as the foot rocks back slightly on the heel. Remember that the deep digital flexor tendon courses down the back of the leg, gliding around the fetlock joint, all the pastern joints, and the coffin joint, to attach on the mid-bottom of the coffin bone (P3). It is this structure that yields the clinical sign of a ruptured or lacerated deep digital flexor tendon since it is the tension on the tendon that pulls and holds the foot flat on the ground. If the suspensory ligament is involved or transected, the fetlock's ability to support weight is greatly diminished, and the back of the fetlock significantly drops closer to or actually touches the ground.

On the other side of the leg are the extensor tendons, with the common digital extensor the main extensor tendon in the forelimb and the long digital extensor tendon the main extensor tendon in the hind-limb. A loss in the integrity of the extensor tendons has little effect on weight bearing, but does affect the ability of the horse to advance the limb properly during motion. Given that the extensor tendons course down the cannon bone, attaching to the dorsal (front) surface of the pastern (P1 and P2) and coffin bone, their effect is to extend the fetlock joint or pull the foot and pastern forward during movement.

So, a horse with a transected extensor tendon generally has trouble advancing the foot and will drag the toe, knuckling over onto the dorsal surface of the fetlock. Some horses quickly learn to "flip" the foot forward so that their weight-bearing surface is parallel to the ground as the foot lands.

Immediate Action

Tendon lacerations are an area where appropriate first aid potentially can prevent increased injury to a damaged tendon and improve overall outcome. The first step is to have the laceration evaluated as soon as possible. Given the location (near the ground) and the usual causative agents of these lacerations (dirty pieces of metal), extreme wound contamination is certain. Remember that the "golden period" for repairing a wound is six to eight hours--getting the wound repaired before this period is up can reduce complications from infection. From the time the laceration is noticed, the gross contamination should be washed away (using warm water and a disinfectant soap such as Betadine) and the wound covered with a well-applied protective bandage. Until the degree of damage can be evaluated by your veterinarian, the horse should be cross-tied or at least confined to a stall to minimize weight bearing and use of the affected limb in an effort to prevent worsening the injury.

Again, it is extremely important to act quickly; the more time that goes by before appropriate treatment, the greater the risk of infection. If serious infection occurs, especially in the area of a tendon sheath, there can be a significant decrease in the prognosis for returning to serviceable soundness.

When the laceration involves a tendon sheath, the prognosis is more guarded since this situation tends to have a much greater complication rate from infections and/or the development of adhesions of the tendon sheath to the tendon. The presence of adhesions can affect the tendon's mobility and can serve as a source of chronic lameness.

Repair And Management

The repair and management of tendon lacerations generally consist of three main goals:

  1. Depending on the extent and location of the laceration, it is evaluated with the horse under heavy sedation or general anesthesia. The wound is debrided and lavaged in an effort to remove any devitalized tissue and reduce the concentration of bacteria and other contaminants.
  2. If the laceration is not severely infected or the cut ends not completely shredded, the tendons are sutured together in an effort to minimize the amount of scar tissue that will form during the healing process.
  3. After wound debridement and repair of the damaged tissues, the leg needs some type of immobilization in order to reduce the tension on the tendons while they heal.

Regardless of how prompt or thorough the repair, the wound still is contaminated and thus generally warrants systemic antibiotics. In addition, tetanus vaccination status of the animal must be evaluated and boosted if necessary, and, of course, pain and inflammation management with drugs such as phenylbutazone often is necessary.

Lacerations of the common or long digital extensor tendons tend to have a better prognosis and are easier to repair and manage than flexor tendon lacerations. If the cut ends of the tendon are sharp and there is not too much infection present, the tendon easily can be sutured together. In the face of ragged tendon ends or significant infection, the tendon often is not primarily re-paired (sutured). In this case, it is allowed to heal with the leg immobilized.

Regardless of whether the tendon is primarily repaired, the leg should be placed into a fiberglass cast or managed with a support bandage with the leg held in extension by a splint. The leg typically is immobilized for three to six weeks. The prognosis for horses with extensor tendon lacerations generally is good.

Lacerations of the flexor tendons are more difficult to treat, more costly to treat, and have a much poorer prognosis for the anima's return to performance than extensor tendon lacerations. This depends on whether the laceration includes one or both of the flexor tendons and the degree of involvement. Generally, the more tendon structure involved, the poorer the prognosis. In addition, if there is any involvement of the suspensory ligament and/or any of the blood vessels or nerves, the prognosis is worse. As mentioned before, if there is involvement of the tendon sheath, there can be additional complications with infection and chronic lameness.

The principles for flexor tendon repair are similar to those for the extensor tendon. If the lacerated tendon ends are not too ragged, and if severe infection is not present in the wound, the tendons are preferably sutured, making a primary repair. A fiberglass cast is necessary to reduce the weight-bearing forces on the tendons. The limb is cast under a mild degree of flexion in order to hold the limb in a position that will reduce the pull on the tendons. After three to four weeks, the cast can be removed and a fetlock support shoe can be used. In some cases, an additional two to four weeks of immobilization using a splint might be required before switching to the support shoe.

The fetlock support shoe essentially creates a sling on which the back of the fetlock cab sits, thereby reducing some of the tension on the flexor tendons. This shoe generally is utilized for an additional three to four weeks. It is not recommended to resume riding or training for six to nine months, depending on the specifics of the case and how the individual horse is healing.

The overall prognosis is thought to be fairly poor for horses with flexor tendon laceration. In a 1995 issue of the Journal of the American Veterinary Medical Association, Scott Taylor, DVM, from the Arizona Equine Medical and Surgical Center in Gilbert, Ariz., and John Pascoe, BVSc, PhD, from the University of California, Davis, reported on "Digital flexor tendon lacerations in horses: 50 cases." In that study, out of the 50 horses, 82% that survived were able to be ridden again, with 39% of those used for athletic activities. It was noted that when only one flexor tendon was transected (with or without partial transection of another tendon), 92% of the survivors were able to be ridden again, with 50% used for athletic activities. In addition, when both flexor tendons were transected, 69% of the survivors were able to be ridden, with 23% of those used for athletic activities. The athletic activities included ranch work, roping, dressage, cutting, harness driving, hunting/jumping, and competitive trail riding.

While appropriate repair and management of tendon lacerations can potentially bring a horse to soundness and serviceability, it is better to try and prevent tendon lacerations rather than treat them. Management is intensive for tendon injuries, the convalescent time is long, and overall the treatment can be costly (anesthesia, surgery, fiberglass casts, antibiotics, and special shoeing can add up to several thousand dollars).

Accidents that are unavoidable can happen, but taking the time to survey your horse's surroundings for potential problems could save you, and your horse, in the long run.

About the Author

Michael Ball, DVM

Michael A. Ball, DVM, completed an internship in medicine and surgery and an internship in anesthesia at the University of Georgia in 1994, a residency in internal medicine, and graduate work in pharmacology at Cornell University in 1997, and was on staff at Cornell before starting Early Winter Equine Medicine & Surgery located in Ithaca, N.Y. He is also an FEI veterinarian and works internationally with the United States Equestrian Team.

Ball authored Understanding The Equine Eye, Understanding Basic Horse Care, and Understanding Equine First Aid, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.

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