Platelets secrete growth factors and other proteins that regulate cell division, stimulate tissue regeneration, and promote healing.

Platelet-rich plasma therapy, sometimes called PRP therapy or autologous conditioned plasma (ACP) therapy, attempts to take advantage of the blood’s natural healing properties to repair damaged cartilage, tendons, ligaments, muscles, or even bone.

A growing number of people are turning to PRP injections to treat an expanding list of orthopedic conditions, including osteoarthritis. It is most commonly used for knee osteoarthritis but may be used on other joints as well.

PRP Injections for Joints

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

  • reduce pain;
  • improve joint function;
  • possibly slow, halt, or even repair damage to the cartilage.

Platelet-rich plasma is derived from a sample of the patient’s own blood. The therapeutic injections contain plasma with a higher concentration of platelets than is found in normal blood.

What is plasma? Plasma refers to the liquid component of blood; it is the medium for red and white blood cells and other material traveling in the bloodstream. Plasma is mostly water but also includes proteins, nutrients, glucose, and antibodies, among other components.

What are platelets? Like red and white blood cells, platelets are a normal component of blood.

Platelets alone do not have any restorative or healing properties; rather, they secrete substances called growth factors and other proteins that regulate cell division, stimulate tissue regeneration, and promote healing.

Knee Osteoarthritis Treated with PRP

Researchers studying PRP and osteoarthritis often work with patients who have knee osteoarthritis, a condition that experts estimate will affect nearly half of all Americans at some point during their lives.

One study, published in 2013, involved 78 patients with osteoarthritis in both knees (156 knees). Each knee received one of three treatments: 1 PRP injection, 2 PRP injections, or 1 placebo saline injection. Researchers evaluated the subjects’ knees 6 weeks, 3 months, and 6 months after injection.

Researchers found:

  1. Knees treated with 1 or 2 PRP injections saw a reduction in pain and stiffness as well as improvement in knee function at 6 weeks and 3 months.
  2. At the 6-month mark, positive results declined, though pain and function were still better than before PRP treatment.
  3. The group that received placebo injections saw a small increase in pain and stiffness and a decrease in knee function.
  4. The platelet-rich plasma used in this clinical study had 3 times the platelet concentration of normal blood and had been filtered to remove white blood cells.

A second, smaller study examined patients who had experienced mild knee pain for an average of 14 months. Each arthritic knee underwent an MRI (Magnetic Resonance Imaging) to evaluate joint damage and then received a single PRP injection. Patients’ knees were assessed at the 1 week, 3 month, 6 month, and 1-year marks. In addition, each knee underwent a second MRI after one year. Researchers found:

One year after receiving a PRP injection, most patients had less pain than they did the year before (though the pain had not necessarily disappeared).

MRIs showed that the degenerative process had not progressed in the majority of knees.

While knee cartilage did not seem to regenerate for patients, the fact that arthritis did not worsen may be significant. Evidence suggests that an average of 4 to 6% of cartilage disappears each year in arthritic joints.

Suggested Indications for PRP Injections for Osteoarthritis

Platelet-rich plasma injections may not be appropriate for osteoarthritis patients who:

  • have a medical condition that could worsen or spread with injections, such as an active infection, a metastatic disease, or certain skin diseases;
  • have certain blood and bleeding disorders;
  • are undergoing anticoagulation therapy (and cannot temporarily suspend treatment);
  • are anemic;
  • are pregnant.

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