Suspensory Ligament Injuries: Mending With Marrow

Suspensory ligament injury is a common problem in athletic horses, and it is often slow to heal, with a high recurrence rate when a horse returns to work. Douglas Herthel, DVM, of Alamo Pintado Equine Clinic in Los Olivos, Calif., has been using bone marrow in a new technique for treating these injuries. He began his study in 1995, looking at bone marrow, which contains stem cells, monocytes, platelets, and fat.

"A recent unpublished survey that was done at UC Davis indicates this is the single most common cause of lameness in the show horse," says Herthel of suspensory ligament injury. "It can affect almost any horse that is in athletic performance.

"The experience we had in treating these during the past 25 years--prior to stem cell therapy--was fairly dismal," he continues. "Ours is a referral practice, and we usually got the cases after they'd been looked at and treated numerous times. We were averaging only 20% success in return to full work."

Most of the horses used in his early studies were in dressage and jumping. "Our basis for using bone marrow in treating damaged ligaments was that it is a tremendous source of tissue healing components--growth factors, stem cells, and matrix," he says. The angiogenesis effect (formation of new blood vessels) is important for healing, along with increase of cellularity, fibroblast (connective tissue cell) numbers, and biomechanical strength. These traits had already been shown with stem cell therapy in rabbit collateral ligament studies.

"Our hypotheses were that horses with suspensory ligament desmitis, treated with bone marrow components from their own body, would hopefully return to soundness more rapidly than horses with conventional treatments, and have a lower rate of recurrence, which is a common problem in suspensory desmitis cases," says Herthel.

In his studies, he started with the worst cases, those with severe suspensory ligament damage. "Diagnosis has become better and more sophisticated in recent years (using ultrasound, nuclear scintigraphy, etc.), and the history of the injury is important, such as change in work load, change in footing (especially in the show horse), and change in shoeing," he says.

In the study, the conventionally treated group consisted of 66 horses, treated between 1991 and 1996. These were generally rested and rehabilitated while given non-steroidal anti-inflammatory drugs. Some were given corticosteroids, and some had ultrasound therapy. The bone marrow-treated group numbered 100 horses treated between 1995 and 1998. Those horses received a single treatment of bone marrow from their own bodies.

How It Works

The procedure requires general anesthesia with the horse on his back, giving easy access to the sternum (breastbone) and to the leg being treated. Ultrasound is used to guide the needles into the lesion. Needles are pre-placed into injection sites, then bone marrow is aspirated from the middle cavity of the sternum. There is no incision. If there are multiple injection sites, and if more bone marrow is needed, another site on the sternum can be used for more marrow.

There is enough air in the bone marrow to show exactly where it is going. "It's basically white on the screen," says Herthel of the ultrasound-guided injection. "You can watch it fill in, and kind of paint it into where you want to go."

Other sites can be used for harvesting bone marrow, but the sternum is used because it is so easy. "We have not used any other sites, primarily because we are happy with this one," says Herthel.

There are only about seven stem cells per 100,000 cells in the bone marrow. Herthel has been asked whether it might be better to isolate and culture the stem cells and get more of them, but his staff did not have the technology to do this, and his biggest concern was to get those cells injected back into the animal within minutes in order to have the most viable cells. There is culturing being done, in other research efforts, but he feels it takes more than just the stem cells to be effective--possibly most of the other constituents of bone marrow.

"Postoperatively, the first couple of weeks consist of stall rest with hand walking or turnout in a small paddock," says Herthel. "We want the horse moving, not just standing. Later on they go to light riding,
Aquatread (an underwater treadmill), turnout, treadmill, or other types of rehabilitation. Early loading (weight-bearing) is crucial to collagen quality and to fiber alignment. Movement stimulates production of collagen, more than in an animal that is totally rested and not stressed.

"In the conventional group, 15.2% returned to soundness within 12 months," he says. "In those with bone marrow treatment, 84% returned to soundness, 8% became somewhat usable, and only 5% did not improve." (Three percent were lost during the study and were not included in the results.)

"We did not notice any complications," he continues. "There were no infections in that group or in any subsequent treatments. There has been one recorded case of pericardial tap (puncture of the pericardium, the fibrous sac that surrounds the heart, during the marrow harvesting procedure), an inadvertent occurrence that caused pneumopericardium (presence of air in the heart cavity) on a horse. That horse recovered and went on to the Olympics, but this complication is something to think about."

This technique has been used on jumpers, dressage horses, endurance horses, and racehorses. "One case was an 8-year-old racehorse with bilateral (both) front high suspensory tears treated in 2000, and when he returned to racing in 2001 (at age 9), he had the fastest race of his life."

A veterinary practice in Germany started doing bone marrow transplants about the same time Herthel did, and veterinarians there reported their results to him in 1998. Their success rates were within 1-2% of his.

Why It Works

"We feel this is a regenerative approach, based on growth factors and cell therapy," says Herthel. "Ligaments heal poorly, and traditional thinking is that it's due to poor circulation, though there are studies showing that's not true. Other problems with ligament healing include low numbers of cells, low fibroblast numbers, and cell matrix ratio decreasing with age and with injury. Injured ligaments have abundant poor-quality collagen, compared to good-quality collagen. Our goals in treatment are to increase the vascularity (blood supply) and oxygen to the tissues, increase cellular fibroblast numbers, increase matrix quality, increase the fiber alignment, and most importantly, return horses to soundness."

Growth Factors

Growth factors have received lots of attention, and they have mechanisms of action that are related to message transmittal, receptors, and target cells. Growth factors are peptides produced in the body that tell other cells to perform certain functions. They are important to matrix formation, cell division, and other critical processes.

"The peptide growth factors are in play at different levels," explains Herthel. "Stem cells are able to replicate extremely well. A person can be transfused with a million stem cells and regenerate their entire immune system.

"In our therapy, we are looking for stem cells going to fibroblasts, and hopefully producing collagen matrix and secreting more growth factors to stimulate replication," he says. "We feel the cell adhesion molecule (a molecule on the surface of animal tissue cells) provides a foothold for the cells as they migrate through the ligament, and the fibrin (protein that builds to form a blood clot) also acts like a scaffold." These foundation structures greatly facilitate healing.

"Some horses need to have multiple ligaments treated," he says. "We've done sacroiliacs and suspensories at the same time. Some tendons are treated with a combination of stem cells and embryonic cells, some with just stem cells and bone marrow. Embryonic stem cells and platelet-rich plasma are some of the things we are working with in experimental models."

His conclusion is that bone marrow treatment is safe, effective, and economical for the horse owner. And possibly for people also, says Herthel. The treatment is being used more often by human orthopedic surgeons in Santa Barbara, Calif., for treating torn Achilles tendons, rotator cuffs, and numerous other ligament tears in people. Exactly the same technique that is being used on the horses is being used in human medicine, and results are promising, he says.

"One patient who had been suffering from a chronic Achilles tendon tear and was experiencing severe pain reported that the pain was relieved the next day after bone marrow injections," Herthel comments.

"The main question is, how does it work? We are not sure, but we are looking forward to the future and finding out more about it," says Herthel.

About the Author

Heather Smith Thomas

Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog,, she writes a biweekly blog at that comes out on Tuesdays.

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