The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.
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28 TheHorse.com THE HORSE June 2017 (using the individual's own tissue to replace a ruptured or injured ligament or tendon) have become commonplace even in top athletes, leading to full recovery. Human doctors have cruciate ligament (which stabilizes the knee joint) surgical repair down to an exact science these days, which involves taking a nearby ten- don and attaching it to the knee where, over a period of months, it "transforms" into a new cruciate ligament. Essentially, the tendon then regenerates itself. So why don't these medical miracles exist for horses? To put it simply, it's im- possible to get a horse to lie in bed during the postoperative healing process, Grisel says. "Graft surgeries require full rest un- til the new tissue attaches, but in horses you really need a structure that's ready to function almost immediately because these animals are constantly moving and accommodating weight-bearing loads." Some researchers have tried using a polypropylene mesh to augment and accelerate tendon repair. While this tech- nique has shown promise for stabilizing displaced tendons, it has not been very effective at replacing torn or ruptured fi- bers. Thus, many of these surgeries failed as well, says Grisel. "There just wasn't enough time to gain strength before the horses started tugging on it, and there were also (tissue) rejection issues," he says. "Plus, additional scar tissue would form around the prosthesis, compromis- ing eventual functionality." Researchers have recently seen better (anecdotal) results when combining mesh implantation with concurrent stem cell graftings, says Grisel. Stem Cell Therapy's Results With the 21st century came the intro- duction of stem cell therapy into equine practice, with the initial idea being to "re- generate" healthy cells to replace injured tissue. With ligament and tendon injuries, that meant rebuilding those structures with tissue that's as similar to native tis- sue as possible and less like scar tissue. A stem cell is an immature and un- specialized cell that's not programmed (differentiated) to be a particular kind of body cell (muscle, blood, skin, tendon, etc.). Embryonic stem cells harvested from a fetus before Day 8 of embryonic development can still form all the body's cell types (they are pluripotent). Adult stem cells, on the other hand, harvested from tissues (anywhere from older than Day 8 of embryonic development through adult horses) are already committed to one group of tissue types (germ line) and are multipotent. For example, mesen- chymal stem cells (MSCs) can be derived from many tissues in the body and can be used to treat a variety of tissues and have donor-tissue-specific tendencies. Thus, it made sense to place these adult multipotent MSCs into injured tendons and ligaments and let them become healthy Collagen-1-producing cells for those structures, and, voila, create brand new tendon/ligament. Early studies in live horses showed that stem cells would grow into healthy Collagen-1-producing cells when placed into a healthy tendon and ligament environment, says Spaas. In practice, however, a horse's own stem cells (often collected from his umbilical cord blood at birth and then stored, or collected from his fat or bone marrow as an adult) ended up serving a Mending Tendons and Ligaments