If a damaged or injured tendon fails to heal with rest and physical therapy, a doctor may recommend injecting platelet-rich plasma (PRP), also called autologous conditioned plasma (ACP). Many experts believe that the natural healing properties found in platelets and plasma facilitate healing and repair in damaged tendons.

When treating a damaged tendon with platelet-rich plasma, the doctor injects PRP directly into the affected area. The goal is to:

  • Reduce pain
  • Improve joint function
  • Repair damage to tendon tissue

While a lot of research has been done in recent years, more large-scale, high-quality clinical studies are needed before scientists can know exactly if and how PRP helps patients who have tendinopathy and related conditions. While research so far is encouraging, PRP therapy is not considered standard practice and insurance plans typically do not cover it.

Tendinitis, Tendinosis, and Tendinopathy Pain

Tendons are soft tissues that connect muscle to bone, and their degeneration may be caused by multiple factors, such as past injuries, aging, stress, and overuse. Tendon damage is commonly referred to as tendinitis, tendinosis, or tendinopathy.

See Chronic High (Proximal) Hamstring Tendinopathy

Tendinitis is an inflammatory condition, but research has shown that most tendon injuries do not exhibit inflammation. Rather, the primary problem appears to be a breakdown of the structural composition (e.g. the amount of essential collagen a tendon contains), strength, and stability. In some cases this degeneration results in chronic pain, disability, or tendon tears. Medical professionals describe this tendon degeneration as tendinosis or tendinopathy.

See What Is the Difference Between Tendonitis, Tendinosis, and Tendinopathy?

How Does PRP Therapy Relieve Joint Pain?

It is unclear how platelet-rich plasma therapy may alleviate tendon pain in some people. Experts theorize that the PRP might:

  • Stimulate healing, including stimulating the production of collagen, which is an important component of tendon and ligament tissue
  • Contain proteins that alter a patient’s pain receptors and reduce pain sensation 1 Descalzi F, Ulivi V, Cancedda R, Piscitelli F, Luongo L, Guida F, Gatta L, Maione S, Di Marzo V. Platelet-rich plasma exerts antinociceptive activity by a peripheral endocannabinoid-related mechanism. Tissue Eng Part A. 2013 Oct;19(19-20):2120-9. doi: 10.1089/ten.TEA.2012.0557. Epub 2013 Jun 6. PubMed PMID: 23578218. , 2 The International Cellular Medical Society. Guidelines for the Use of Platelet Rich Plasma. Adopted 2011. http://www.cellmedicinesociety.org/attachments/370_Section%2010%20-%20Platelet%20Rich%20Plasma%20%28PRP%29%20Guidelines.pdf Accessed August 15, 2013.

Researchers are still learning how PRP might work.


What Are Platelets and Plasma?

Platelet-rich plasma is derived from blood. A blood sample from the patient is processed using specialized medical equipment to produce a therapeutic injection(s) that contains plasma with a higher concentration of platelets than is found in normal blood.

  • Platelets are a normal component of blood, just like red and white blood cells. Platelets release substances called growth factors and other proteins that regulate cell division, stimulate tissue regeneration, and promote healing. Platelets also help the blood to clot.
  • Plasma refers to the liquid component of blood. It is mostly water but also includes proteins, growth factors, nutrients, glucose, and antibodies, among other components.

Interestingly, there is no universally accepted formula for “platelet-rich plasma,” so a PRP injection that one patient receives can be very different than that of another depending on the method of PRP preparation, or the patient’s own blood composition.


How Is PRP Made?

Methods vary, but the most common way to prepare PRP involves centrifuging a patient’s blood sample. A vial of blood is placed in a centrifuge, where it is spun at intensely high speeds. The spinning causes the blood to separate into layers:

  • Red blood cells, approximately 45 percent of blood, are forced to the bottom of the vial.
  • White blood cells and platelets form a thin middle layer, called a buffy coat, which comprises less than 1 percent of the centrifuged blood.
  • “Platelet-poor” plasma, or plasma with a low concentration of platelets, makes up the remaining top layer, about 55 percent of the centrifuged blood sample.

Once the centrifugation process is complete the doctor or medical technician will remove the vial from the centrifuge, extract the necessary blood components for PRP, and prepare the PRP solution for injection.

Find out how preparation methods and other factors can affect PRP.

Dr. John Wilson is a family medicine and sports medicine physician at UW Health. He specializes in treating arthritis and sports-related injuries. Dr. Wilson is an Assistant Professor in the departments of Family Medicine and Orthopaedics at the University of Wisconsin-Madison. He also serves as a physician for the football and wrestling teams at the University of Wisconsin-Madison.