Tendonitis of the superficial digital flexor tendon (bowed tendon) and suspensory ligament desmitis are common injuries of athletic horses that can be recalcitrant to treatment, resulting in significant economic loss to the equine industry. In addition to loss of performance due to suspensory desmitis, suspensory ligament injuries are is believed to predispose horses to catastrophic breakdown injury and condylar fractures.
Scientific investigations into the causes of tendon and suspensory injuries are limited; however, multiple factors appear to play a role. While tendonitis and desmitis are two distinct clinical entities, the most commonly proposed causes for both conditions include overuse and overload injuries. Therapeutic approaches to tendonitis/desmitis are also similar and 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 may ultimately improve the quality of repair, improve the prognosis for return to performance, and decrease the incidence of re-injury.
Numerous growth factors have been investigated to enhance the synthesis, and diminish the loss of tendon/ligament tissue. The use of bone marrow aspirates to deliver a combination of growth factors has been used clinically for the last 10 years for treatment of equine SL desmitis, with Herthel reporting an 84% return to athletic function. Although there are no published reports regarding its use, it has been widely adopted clinically. Similarly, several practitioners are withdrawing venous blood and injecting it directly into tendons/ligaments under the assumption that they are providing a combination of growth factors to the injured site. Most recently, the use of platelet rich plasma has been investigated for augmented tissue repair.
Platelet rich plasma (PRP) has been used for several years in oral and maxillofacial surgery to accelerate peri-implant soft tissue and bone healing. There are also preliminary investigations into its use in defects of bone and cartilage. PRP is exactly what its name suggests. The substance is a by-product of blood ( p lasma 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 and desmitis arises from the combination of growth factors released from the platelets at the site of injury. Two additional incentives for using PRP in tendon and ligament repair include its availability (PRP is made patient-side by simple centrifugation) 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 the platelets receive the attention when considering PRP for tissue repair, there are also several proteins released by platelets 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 the PRP preparation will dictate the final outcome.
The studies outlined in this proposal are designed to determine the effects of a variety of blood products on the metabolism of equine tendons and ligaments in culture. The studies are designed to determine both the stimulatory and potentially detrimental side effects of blood products on tendon and ligament metabolism. The expectation is that these studies will provide immediately clinically relevant information regarding the efficacy and potential safety of blood-derived products for tendonitis and desmitis.