- Dr. Lisa Fortier
Dr. Lisa Fortier
Tendonitis of the superficial digital flexor tendon (bowed tendon) is a common injury of athletic horses that is often recalcitrant to treatment, resulting in significant economic loss to the equine industry. Scientific investigations into the causes of tendon injuries are limited and multiple factors appear to play a role. However, the most commonly proposed causes for tendonitis include overuse and overload injuries. Therapeutic approaches to tendonitis include acute therapy such as icing and bandaging, and rehabilitation exercise. While such traditional methods of treatment are valuable, they do not focus on improving the cellular response to injury. Enhancing the healing response on a cellular and molecular level with growth factors may ultimately improve the quality of repair, improve return to performance, and decrease the incidence of re-injury.
There are several newer biological, regenerative therapy-based treatment modalities for tendonitis including stem cells and platelet rich plasma (PRP) which is a concentrated milieu of the body’s growth factors. Although use of stem cells for the treatment of tendonitis appears promising, they can be expensive and are not presently available for use at the time of diagnosis. In contrast, PRP can be made patient- side, at the time of diagnosis by a simple, 10-15 minute centrifugation of the patient’s blood, and then applied to the site of injury.
Platelet rich plasma (PRP) has been used for several years in oral and maxillofacial surgery to accelerate soft tissue and bone healing. Data from our laboratory supports the use of PRP to enhance tendon matrix synthesis (see Appendices 1-3) and there is one small case-series where Standardbred race horses with suspensory desmitis were successfully treated with PRP.1 PRP is exactly what its name suggests. The substance is a by-product of blood (plasma is the straw-colored liquid in which the blood cells are suspended) that is rich in platelets. PRP is generated through a simple centrifugation of blood. In the body, platelets perform many functions, including formation of a blood clot and release of growth factors into a wound. The rationale for the use of PRP in the treatment of tendonitis arises from the combination of growth factors released from the platelets at the site of injury. Two additional incentives for using PRP in tendon repair include its immediate availability for application and it will not be rejected by the patient’s immune system since it is made from the patients’ own blood.
Although the growth factors contained in platelets has been the primary focus when considering PRP for tissue repair, white blood cells are also concentrated in most commercially available machines, albeit to a lesser degree than platelets. There are several proteins released by white blood cells that could incite an inflammatory response. Thus, PRP likely contains proteins with both positive and negative effects on tissue regeneration and the balance of proteins in a PRP preparation will dictate the final outcome. In fact, data from our laboratory indicates that there is a positive correlation between platelet and matrix synthesis, a negative correlation between white blood cells and matrix synthesis, and a positive correlation between white blood cells and matrix degradation. In other words, white blood cells lead to not only less tendon regeneration but they also can lead to loss of normal tendon tissue. Collectively, these data imply that a PRP preparation with high white blood cell concentrations could in fact exacerbate an injury through increased inflammation and tissue loss while preparations with low WBC concentrations would not. The challenge is determining what combination of white blood cell and platelets is optimal.
The broad objective of the studies outlined in this proposal is to determine the optimal preparation of PRP, with respect to platelet and white blood cell concentrations. There are at least 6 companies that manufacture equipment to generate PRP. Our goal is not to perform a head-to-head comparison of the products from these companies, but rather to set out to systematically determine what the optimal preparation should be in order to maximize tendon healing and mitigate the degrading effects of white blood cells.
The expectation is that these studies will provide immediately clinically relevant information to help equine practitioners make intelligent choices between various PRP products. Further, once an optimal PRP preparation is identified and put into clinical practice, then clinical studies can be designed with similar PRP products and treatment outcomes can be more accurately assessed.