Ligaments connect bones to bone. In the horse they, along with tendons, hold their bones in place and orchestrate muscle mobility. Photo by Stephanie L. Church

It’s not uncommon for racehorses to experience ligament injuries at some point in their careers. Let’s examine how these ligament injuries occur, the treatment options available, and the best ways to navigate second (or even third) careers following recovery.

Ligament Injury 101

The basic purpose of our horses’ tendons and ligaments is essentially to hold their bones in place and orchestrate muscle mobility. Tendons connect muscles to bones, while ligaments connect bones to other bones. So, what leads to ligament injuries in horses?

“Ligament injuries can be caused by repeated strains in soft tissues and tendons or may have a prior degenerative component,” says Stefanie Hansen, DVM, MS, assistant professor of Large Animal Surgery at Michigan State University, in East Lansing. “These injuries can also be caused by a single acute trauma, such as the horse falling or taking a bad turn. Those injuries can be fairly significant.”

Often, ligament damage occurs due to the structure being strained over time. Researchers have not identified any genetic disposition. However, Hansen points out imbalances due to conformation or shoeing can predispose horses to ligament injury. “This is especially important for suspensory branches, as this will cause uneven wear and tear,” she says.

For example, horses that have straight hocks, dropped fetlocks or are offset in the knees can elevate strain on the suspensory ligaments. “Any sort of conformational abnormalities can put more strain on both the ligaments and the joints that can make them more susceptible to injury,” says Hansen—and these abnormalities can sometimes be corrected. “The farms work very closely with their veterinarians to make sure we give the horses the best possible conformation. This is why we’re doing transphyseal screws and correcting their feet at an early age to keep them as straight as possible.”

Timingwise, equine surgeons can complete fetlock corrections (distal metacarpal physis) before foals reach 3 months old, and they can perform knee correction (distal radial physis) when animals are 10 to 15 months of age.

“More correctly conformed horses are better balanced, reducing the chance of a site of overload and injury,” explains Lawrence Bramlage, DVM, MS, Dipl. ACVS, a world-renowned equine orthopedic surgeon at Rood & Riddle Equine Hospital in Lexington, Kentucky. “The higher the level of exercise anticipated, the more important it is that a horse has more correct conformation.”

Types of Ligament Injuries in Horses

Common signs of ligament injuries include lameness, decreased performance, swelling, heat, soreness, inflammation and visible fibrosis (thickening).

As for terminology, “A strain indicates just swelling of a ligament, a sprain indicates some fiber damage and a rupture indicates all fibers of a ligament have been disrupted,” says Bramlage.

Of many ligaments in the body, one in particular, which we’ve already mentioned, stands out in racehorses.

“The most common one we deal with, daily, is the suspensory ligament, which runs from back of the knee and hock down to the fetlock,” Hansen explains. “When you hear about ‘breakdown injuries,’ this is, in addition to the fracture, one of the ligaments we’re talking about as it plays an important role in supporting the fetlock.”

In the horse, the suspensory ligament originates at the proximal aspect of the cannon bone (just beneath the knee or hock) and distal (bottom) row of carpal bones. It runs in the groove between splint bones and distally splits into two branches that insert on the medial (inside) and lateral (outside) proximal sesamoid bones (at the back of the fetlock). Both proximal suspensory injuries and branch injuries are common.

“It can be unilateral or bilateral; it’s not uncommon for it to be seen in more than one limb,” says Hansen. “There are ligaments everywhere, but the suspensory is one of the more common ligaments injured in both Thoroughbreds and sport horses.”

Treatment Options for Ligament Injuries in Horses

Treatment protocols can vary.

“The site of the injury, the severity of the injury and which structures are injured all dictate different approaches,” says Bramlage. “Strains can often be treated with medication and a short rest. Sprains require time for the torn fibers to heal; stem cells can help some of these injuries. Ruptures often don’t ever heal well enough for high-level athletic activity.”

“Treatment depends on, first of all, the type of lesion, which can be anything from a little bit of changed fiber alignments or swelling (sprain), to more extensive fiber disruption, which typically means there is an area of edema (fluid swelling) within the ligament where fibers are torn completely,” says Hansen. “Tendons and ligaments in general heal very slowly because of the poor blood supply versus bone, which heals better. Rest is important to decrease the strain on the ligament while it heals.”

Treatment protocols could include up to six months of stall rest, extracorporeal shock wave therapy to stimulate healing and provide pain relief and an array of biologics, including stem cells.

“Stem cells are becoming more commonly used,” says Hansen. “The main goal is to improve the quality of healed tissue. The problem with ligament injuries is that the tissue will never become the same quality as before, unlike with a bone. Biologics such as stem cells can help control the healing environment, putting down the best quality tissue that the body can.”

Uncovering Stem Cell Success

In 2023, Hansen, Bramlage and Moore published “Thoroughbred racehorses with suspensory ligament branch desmitis treated with mesenchymal stem cells.” In this study they observed orthobiologic treatment of suspensory ligament branch desmitis in Thoroughbred racehorses—specifically assessing racing performance post-injury in horses treated with mesenchymal stem cells (MSCs).

They found that of 69 treated horses, 71% raced post-injury. Horses with a previous race record were more likely to return to racing following treatment, at 90%. Comparatively, mares were less likely to return to racing after injury, at 52%, given their value as broodmares. The study authors reported that of horses that raced pre- and post-treatment, the number of races and earnings “were not significantly different.” Finally, the average career length of all horses that raced post injury was 29.5 months.

Key Takeaways

“The paper we published showed treatment with stem cells more than doubled the probability of a horse staying sound and being able to race if they have a suspensory ligament branch injury, which is the injury we researched,” says Bramlage.

“For me, the key takeaway from this study is that even in the Thoroughbred racehorse with a significant suspensory branch injury, that historically has a poor prognosis, we were able to treat these severe injuries and have horses successfully go back into racing,” adds Hansen. “It shows we shouldn’t just give up on those horses.”

The Future of Treatment

While stem cell treatment has become a more viable and common option for managing equine ligament injuries, it can be expensive and is not accessible to everyone. However, such treatment of ligament injuries can make a difference later in the horse’s career, even after racing, says Hansen. Stem cells help improve the quality of healed tissue by controlling the microenvironment responsible for healing the injured tissue.

“The hope is that stem cells can also, for second careers, make horses more competitive and reduce reinjury rates—although that is not fully supported in current literature yet,” she says. “Reducing reinjury rates makes it possible for horses to be more successful in a second career, as well as if racing.

“I love a good off-track Thoroughbred,” adds Hansen. “A Thoroughbred is a lovely horse to do everything with.”

Second Careers after Ligament Injuries in OTTBs

Nelda Kettles of Oklahoma-based Horse and Hound Rescue Foundation has seen her share of ligament injuries. Alongside her husband Larry, they raced Thoroughbreds for 30 years before founding the Thoroughbred aftercare organization.

Kettles describes the common ligament injury rehabilitation process at their aftercare organization: Coming from good owners and trainers, horses have already had their initial veterinary workups for diagnosis and started treatment. “Our vet will do ultrasounds, making sure the fibers are healing correctly. There is initially stall rest, then small turnout, then larger turnout. I tend to be on the more cautious side. I don’t put the horse into any training until at least nine months after the injury. To me, if you push it, you’re taking too big a chance on reinjuring.”

It’s key to consider “any weak spot” or known injury when considering an OTTB’s next career. However, second careers for horses with these injuries are definitely doable, says Hansen. “It is dependent on the degree of injury,” she explains. “Many sport horses walk around with some degree of (previous) injury and do fine. For significant injuries, it can be hard to keep them athletic as either racehorses or sport horses.”

Horse and Hound Rescue Foundation has secured second careers for more than 500 Thoroughbreds, with 52 adopted in the past year alone. Kettles works closely with owners, trainers and veterinarians to match horses to their best next career.

“They can be great trail horses and great dressage horses, especially for those with beautiful movement,” she says. “Anything that does not have the potential for stressing that tendon or ligament, the horse may be well suited.”