For some time now, it has been suspected that horses with tendon injuries benefit from injection of the area with blood plasma rich in platelets. The procedure may lead to better tendon repair and a final result that is closer to the pre-injury state. There may be slightly faster healing as well. Large, well-controlled clinical trials are lacking, but the anecdotal evidence is strong enough that many large-animal veterinarians use this type of medical therapy on a regular basis.
Platelet-rich plasma has become folded into therapies for people, too. Golfer Tiger Woods has received injections in his knee, as have pro football and baseball players for their own tendinitis-like injuries. Physicians have also been using plasma-rich platelet therapy since the mid 1990s in human patients to aid bone healing after spinal surgery and soft tissue healing after plastic surgery. Other applications are being tried as well for the healing of ligaments and muscles.
“Platelets have a lot of growth factors and molecules called cytokines that are mediators of inflammation,” says Tufts veterinarian Michael Kowaleski, DVM, an orthopedic specialist who treats dogs and other small animals. “It’s believed that the release of the growth factors could stimulate tendon healing by bringing new, healthy cells to the site of the problem while some of the cytokines help reduce inflammation.”
Now researchers are taking the thinking further. Dr. Kowaleski says that because of the substances in platelets, it’s believed that platelet-rich plasma might be able to ameliorate the pain of arthritis in dogs. For that reason he’s conducting a study on arthritic dogs, mostly Labrador retrievers, Bernese mountain dogs, and German shepherds. All the dogs enrolled in the trial have arthritis in both elbows in their front legs, usually from canine elbow dysplasia — a developmental condition that worsens as the dog grows during puppyhood.
Plasma-rich platelet therapy, or PRP, “won’t fix the joints,” Dr. Kowaleski notes. That is, growth factors in the plasma won’t heal the damaged joints. “But together with the cytokines, they may act as pain relievers.” One of the reasons is that if there’s less inflammation as a result of the release of certain cytokines, there’s less pain.
Where does the platelet-rich plasma come from?
The plasma injected into the dogs comes from their own blood. After it is taken from the dogs, it is put through a process to concentrate the platelets. That’s done by removing the red and white blood cells and leaving behind just the blood’s fluid (plasma) and platelets. How do you remove the materials you don’t want?
Normally, that task is completed with an expensive centrifuge. The blood is spun very, very quickly so that all the cells go to the bottom, the platelets to the middle, and the plasma to the top. Then you suction off the parts you want. But the Tufts study is using a special filtration device produced by the Pall Corporation “that’s like a blood bag you use to collect blood when it’s donated,” explains Dr. Kowaleski. “You put the blood in, and it drips through a filter in which all the platelets get trapped. Then you flush it through and all the platelets end up on the other side. You don’t need the expensive equipment.”
The research protocol
Each dog entered into the Tufts trial remains a study subject for 36 weeks — nine months. They are evaluated before they receive an injection into the elbow joint and then at weeks 12, 24, and 36. Not all dogs receive their own platelet-rich plasma. Some receive a control substance — a placebo in the form of sterile saline — while others are injected with hyaluronic acid. That’s an off-the-shelf treatment for arthritic joints that ought to have some kind of positive effect. Whether the effect is more or less positive than the effect of the platelet-rich plasma is part of what the researchers are investigating.
The study is randomized — which dogs are injected with which substance is a random decision — and also blinded. Owners don’t know which solution their dog receives. At weeks 12, 24, and 36 they fill out what is called the Canine Brief Pain Inventory that asks them to rate their dog’s pain over the previous seven days on a scale of one to 10 and also asks how their dog’s pain has interfered with such functions as general activity; enjoyment of life; ability to rise to standing from lying down; ability to walk; ability to run; and ability to climb stairs or curbs.
Dr. Kowaleski is not relying solely on the owners’ blinded assessments. He and his co-investigators are also measuring with precise numbers the force with which the dogs can walk across a platform during and at the end of treatment. That’s critical. The more force, or pressure, a dog can put on his or her leg, the less the arthritis pain is interfering with function.
In addition, the scientists are looking at force multiplied by time — how long a dog stands on the treated leg at a walk.
“We’re about two thirds of the way through” the trial at this point, says Dr. Kowaleski, and it’s too early to make heads or tails even of the interim results. But he and his co-investigators are hopeful. There has already been some research on platelet-rich plasma in people with osteoarthritis of the knee, and their pain scores decreased while their function scores improved. But that was just one study; more research will tell. And we’ll certainly keep you posted on the outcome with the dogs at Tufts.
But even if the results are positive, Dr. Kowaleski says, “it’s critical to understand that being given injections of platelet-rich plasma is like taking a pain reliever. It doesn’t fix the problem. It may take away pain for some period of time. It’s conceivable that dogs are better at month three and better still at month six. But by month nine, the effects may wear off a little.”
The good news, he says, is that if the treatment does prove to be effective, “there’s no downside to giving more injections” as there is with, say, steroids. “We’re giving the dog autologous PRP,” he says. It’s from the dog’s own body and therefore won’t prove toxic with repeated applications. Stay tuned. n