A fresh look at regenerative therapies
by Hope Ellis-Ashburn
Just as the connections of last year’s top pacing colt, Monte Miki, were undoubtedly looking forward to an exciting 2022 season, tragedy struck. Presenting with a bump on the side of his tendon, the colt was diagnosed with a 20-percent tear following a routine work session this past spring, proving that even the most elite athletes are not immune to this common ailment. The injury was serious enough to prompt the colt’s retirement to the breeding shed.
Some horses recover from tendon injuries, while others—like Monte Miki—never race again. What makes this type of injury so troubling, and what are the potential cures?
What Causes a Tendon to Tear?
Tendons have the important job of attaching muscles to bones. They are made up of elastic structures called fibers, which stretch until they get to a point that they can’t stretch anymore and then tear.
“But nobody really knows why they tear,” said John Reichert, DVM, a veterinarian at Woodland Run Equine Veterinary Facility near Scioto Downs who has seen more than his share of tendon injuries in his 32 years of racetrack practice. “The most common location for tendon tears in Standardbreds is the superficial digital flexor tendon.”
He acknowledges that there appears to be a genetic component in some bloodlines that predisposes some horses to getting tears. However, tears can occur anywhere at any time, even in optimal conditions—but they are seen most frequently on deeper tracks.
Conformation can also play a role.
“A horse that stands back at their knees tends to put more pressure on the structures on the back of the leg rather than the front,” Dr. Reichert said. “But we also see horses with conformational defects that never have any trouble, and ones that you would consider as having perfect conformation end up with a tendon injury.”
In essence, it’s a crystal ball question as to whether a tendon injury will occur.
When the Worst Happens
Visible swelling, soreness to the touch, or soreness on the track are typically first noticed by the caretaker or trainer. Some horses with tendon tears remain sound, while others present with a head nod that corresponds with the affected limb.
If a suspected tear occurs, the affected leg should be kept cold until the vet arrives. This can be accomplished through an alcohol rub or sweat, or even cold hosing. Whether the suspicious injury can be “rubbed out” is often the first clue as to its seriousness.
The attending veterinarian will first perform a physical examination that often includes the opposite leg as the first step in the diagnostic process.
“A lot of times, if there’s a tear, you can elicit a pain response at the location of the tear and go from there,” Dr. Reichert said.
The next step in the diagnostic process is usually the use of an ultrasound machine so that the leg’s internal structures can be viewed.
“The ultrasound machine tells us, number one, if there’s a tear, and number two, how big a tear there is and the location of the tear,” Dr. Reichert explained. “After that, we try to make the best judgment as to what the treatment options should be.”
While it is possible to make an educated guess, some horses respond well to treatment while others do not.
Forging Ahead Post-Diagnosis
“Tendons and ligaments don’t have a very good blood supply,” Dr. Reichert said. “Because of that, it takes them longer to heal. The idea is that, with inflammation, the blood goes to the inflamed area. That’s how you see swelling and how healing agents within the blood are carried to that area. But, the structures themselves don’t have a very good blood supply. They take longer to heal than the average muscle injury or even joint injury.”
Recovery from tendon injuries can be a lengthy process. And in Standardbreds, the location of the tendon lesion can affect the speed at which healing occurs.
“Edge tears, particularly an outside edge tear, in my experience seem to heal quicker than ones in the core of the tendon because in the core of the tendon the blood supply is limited and thus takes longer to heal,” Dr. Reichert said, adding that another factor that affects both the rate of healing and the response to treatment is the pressure on the tendon. “Just by nature of the animal, most of the weight is distributed down the inside of the leg so there’s less pressure on the outside edge of the tendon. Those tendon tears [with less pressure on them] tend to do better.”
Before State-of-the-Art Therapies
Tendon tears are not new, and iodine-based paints are one of the oldest treatments available for them.
“You’re treating them topically as a leg tightener,” Dr. Reichert explained.
Cryotherapy is another option that has been around for a while, he said.
“This is a different theory because [rather than reducing], it actually creates more scar tissue around where the tear is and is thought to help support the tendon.”
Regenerative therapies are now on the cutting edge. In his practice, Dr. Reichert makes use of platelet-rich plasma (PRP) and stem cell therapy. Less common is the use of interleukin-1 receptor antagonist protein (IRAP) therapy, now more commonly used to treat issues with the joints.
Stem cell therapy is best implemented in the early stages of the injury after the cooling-out period, which can take from five to seven days. To maximize the opportunity, stem cells should be harvested as soon as the treatment decision is made. It can take a couple of weeks for the tissue to be cultured and processed.
“The time clock is going because you want to get it back and injected while the lesion is relatively fresh,” Dr. Reichert said.
The main source of stem cell retrieval in horses is adipose—or fat tissue—taken from around the tail head. This retrieved tissue is then cultured or processed and injected back into the horse at a later time. However, in recent years, another option for tissue retrieval has come into play: getting it from the umbilical cord at birth.
“The tissue from the umbilical cord is supposed to be the best for a particular horse in terms of deriving stem cells to inject culture and then inject back into the lesions on the tendons,” Dr. Reichert said.
Some yearlings are going through sales and being marketed as having already had their stem cells harvested at the time of birth. Regardless of how stem cells are harvested, a single-dose treatment is usually effective. However, the treatment can be repeated multiple times, if necessary.
“The idea is that you get healing power from these stem cells over several months,” said Dr. Reichert. “You are injecting it right into the lesion. While it doesn’t necessarily speed up healing, it does help the injury to feel better.”
There has been some evidence to suggest that during the waiting period to inject stem cells, PRP can be injected to jumpstart the healing process. PRP can then be reinjected with the stem cells once they arrive.
“PRP is something we can do relatively quickly,” Dr. Reichert said. “There are different options and different kits that are available that a lot of veterinarians have that you can do right on the spot in a matter of minutes.
“The main point with any of these treatments is to minimize scar tissue. Scar tissue is less elastic than the original tendon. You want to minimize scar tissue where the tear happened because it is less elastic.”
Scar tissue sets up the possibility that at some point the tendon may tear just above, just below, or right next to the old lesion.
Cutting-edge therapies do not come cheap. For example, PRP can cost anywhere from $600 to $1,000, and stem cell therapy ranges from $1,500 to $2,500. The likelihood of successful recovery—regardless of treatment—should be compared against the financial investment before the decision is made to move forward.
Best Chances for Success
Size is generally one of the biggest determining factors as to whether recovery will be successful.
“The bigger the tear, the less likely that you are going to have a good outcome,” Dr. Reichert said. “When you have horses with a five-percent or 10-percent tear, the likelihood of them coming back and racing successfully is greater than that of a 20- to 25-percent tear. We see tears all the way up to 50 percent. Certainly, when you have that, your success rate is dramatically less.”
Regardless of the treatment route you choose, rest is an important component that provides the best chance of a long-term future for the horse as a racehorse. Initially, there is a minimum of 30 days of stall rest, but it could be even longer if warranted by the size and location of the injury.
“After the stall rest period, you can consider hand-walking,” Dr. Reichert said.
Ultrasounds conducted throughout the healing process aid in determining when the tendon appears solid and the horse can advance to turnout or jogging. But it’s important to note that, even after it looks solid on the ultrasound, healing continues for a period of months. The longer the horse is away from the racetrack, the better off it is.
Unfortunately, a return to the racetrack isn’t always possible. For breeding animals, at least, there are other options.
“A stallion career or a career as a broodmare would be OK,” Dr. Reichert said.
With so much at stake, the thought of preventing tendon injuries in the first place is foremost in everyone’s mind. But prevention is difficult when so little is truly known about these injuries’ causes. Still, Dr. Reichert has some recommendations:
“Avoid training on really deep tracks. If you have a track that can’t take a lot of water, and it gets really deep, certainly a deeper track is tougher. In my experience, horses training on a deep track are more likely to sustain soft tissue injuries. Even in the springtime, if you’re training up north, the time to avoid training a horse that has had trouble before is during a freeze and thaw where the tracks tend to be really deep. You are better off training on a frozen track than on a deep one where the frost is not yet out of the ground.” HB