New Treatment For Tendon Injuries.

It’ a common-enough occurrence: A horse bows a tendon, is put out to pasture for six to 12 months and returns to work, only to injure himself. As is the case with so many other leg-related problems, with bowed tendons, a lot of it has to do with luck: If you’re lucky, your horse never sustains such an injury; or if he does, it only happens once.

“Most bowed tendons are due to repetitive stress injury and not a one-time traumative episode,” says Dr. Lisa Fortier, an assistant professor of equine surgery at Cornell University’s College of Veterinary medicine in Ithaca, New York. “Tendon and suspensory ligaments are difficult to heal, and even if they heal, a very large majority of them re-bow, either in the injured leg or in the other leg as a result of the stress that has been placed on the injured leg.”

There are two reasons that tendon injuries are so difficult to heal: Tendons have a limited blood supply, and there are a few cells residing in tendon tissue.

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“The cells are important because they can remake the matrix – the tissue around the cells – and complete tendon healing requires proper assembly of the matrix,” Dr. Fortier explains.

Most of the time, when the tendon does not repair itself, the resulting scar tissue isn’t as flexible as the original matrix.

“It can’t function to stretch up and down like a rubber band because it heals in a big knot of scar tissue that is not as elastic as the original tendon,” she says. “That is why they either re-bow in the same area or the knot is so tough that they bow below or above it.”

Not a Matter of Luck

Stem cell researchers are working to remove luck from the equation. By injecting stem cells into the site of the injury, they argue, tendons and ligaments reconstruct themselves, and the horse is able to resume training.

“Stem cells reside everywhere in your body, from your intestines to your skin and in your muscles,” says Dr. Fortier, whose research is focused on cell development. “There is a very small population of stem cells in all tissues of your body that are naturally there. You continually lose cells, and (the replacements) need to come from somewhere.”

There are two different types of stem cells: embryonic stem cells and post-natal stem cells.

“A stem cell is a cell that can turn into a number of different things: cartilage, tendon tissue, bone, fat and some types of neural tissues,” says Hugo Le Messurier, general manager at Vet Biotechnology Ltd. in Kent Town, Australia. “The body uses these stem cells to create these tissues as the individual is growing, and also to continue to repair those tissues as the individual lives and gets older. They are the body’s natural repair cells.”

Vet Biotechnology treats tendons and ligament injuries featuring core lesions.

“When a tendon or ligament is injured, the hole in the tendon will be cleaned out, and the body will remove all of the injured tissue,” Hugo says. “The tendon will get hot, and it will expand, and that is because the body is cleaning all of the old tissue out. After about a month, that core injury – or that hole in the tendon – is ready for new cells to come in and for new tissue to grow.”

Because stem cells re-form the original tissue, the site of the injury remains flexible.

“Instead of allowing the body to heal naturally with scar tissue, we will inject stem cells into that lesion,” Hugo says. “Those stem cells will then create an elastic tissue in the tendon.”

Once the stem cells are injected, the responsibility is on the horse owners and their veterinarians to rehabilitate the animal accordingly. Vet Biotechnology suggests a special 12-month program that was developed by the Royal Veterinary College in England.

“That rehabilitation program will allow the tendon or ligament to recover with elastic tissue so that the horse can get back to work,” Hugo says.

Only veterinarians who have been trained by Vet Biotechnology can use the company’s service, according to Hugo.

“In a standing sedation, they will remove bone marrow from the horse’s sternum and then withdraw bone marrow from the horse. It leaves a couple of little puncture wounds in the horse. They receive a slight sedation, so they are a bit groggy, but when they walk out, they are fine,” he says.

The sample then goes to Vet Biotechnology’s lab, where the stem cells are isolated from the bone marrow. During the course of a couple of weeks, the stem cell supply is expanded and sent back for injection into the horse.

“Then the lab will send the cells back to the vet; the vet will directly inject then into the tendon of the horse under a standing sedation. Once those cells are in there, they bandage the horse up, and the horse walks out,” Hugo says.

Vet Biotechnology also collects stem cells from the umbilical cord of a foal to store in case of future injury.

“When a foal is born, the vet will collect the umbilical cord, send it into the laboratory, and our laboratory will isolate the cells and cryo-store them,” Hugo says. “If the animal injuries itself and it’s a tendon or ligament injury, we can supply the cells very quickly.”

Because the stem cells that are re-injected into the animal are from the actual horse itself, there is no chance of rejection, Hugo says. In Australia, the cost of the procedure is between AU $3,000 and AU $6,000, depending on the veterinarian.

Vet-Stem Inc., based in Poway, California, extracts stem cells from the fatty tissue under the horse’s tail. The tissue is processed at the company’s lab and then sent back to the veterinarian who injects the stem cells directly into the site of the injury. Currently, Vet-Stem treats tendon and ligament injuries.

Dr. Travis Meredith at Vet-Stem touts this treatment because it calls upon the animal’s own healing capacities.“Stem cells are regenerative,” he says. “Where the body’s normal response is to try to heal and stabilize by initiating scar tissue or fibrosis; stem cells actually stimulate and provide regeneration of the damaged tissue. If you put stem cells into an injured tendon, they are going to form into tendon cells. If you put them into a fracture, they will differentiate into bone cells.”

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Dr. Meredith says that for treatment of tendons, this procedure should take place within 30 days after the injury.

“That changes a little bit when we talk about other injuries,” he says. “Suspensory ligaments have a different structure, and there is a significant portion that is attached to the back of the cannon bone. We have seen beneficial effects on cases of suspensory injuries to a year after they occurred.”

Stem cells have different functions for a different disease, he adds.

About 80 percent of the nontrack horses treated under Vet-Stem return to work after six months, Dr. Meredith says.

“Using stem cells gives you the maximum opportunity to return the horse to its original level,” he says. “You are not going to exceed the horse’s original level, but it is the only therapy that will give you the maximum opportunity to return that horse to where it was.”

Success is contingent upon a solid rehabilitation program.

“The first thing that I recommend is to work hand-in-hand with your veterinarian to develop a patient-specific rehabilitation program,” Dr. Meredith says. “Tendons heal best when they heal under load, or tension. We start hand-walking the horses for very brief periods the day after the procedure is done; we don’t typically recommend that they be stalled for 30- or 60-day intervals.”

While nonsteroidal drugs can be used during the acute phase of the injury, steroids are not suggested, as they work against the stem cells. Dr. Meredith notes that, depending on the veterinarian, Vet-Stem’s treatment adds about $2,000 to the cost of traditional tendon rehabilitation.

Because stem cells are “undifferentiated” – which means that they have yet to develop into tissue – they are ideal for the treatment of tendon and ligament injuries, which are generally difficult to fully overcome, Dr. Meredith argues.

“They reside there in storage until the body calls them when it’s injured. Naturally what those cells would do is migrate to that site of injury and then differentiate into the type of tissue that is needed at the time,” he says. “In a tendon injury, they would migrate to the site of the tendon and then differentiate into tendon cells. The problem is, certain organs and certain structures have a decreased ability to heal. What our process does is allow us to utilize the body’s own cells and allow your veterinarian to deliver your horse’s own healing capacity right to the site of the injury.”