Platelet-rich Plasma or PRP injections for joints and tendons are becoming more popular. They form part of the new field of regenerative medicine, used in joints and tendons to reduce pain and promote healing. But is there evidence that PRP therapy works for conditions such as arthritis and tendonitis?

What is Platelet-rich Plasma?    

In summary, platelet-rich plasma, or plasma therapy, is a blood sample with a concentration of platelets greater than that of whole blood.

Platelet-rich plasma (PRP) is derived from whole blood. We obtain blood from a vein in the patient’s arm. The blood spins into different layers: red, white, and plasma. The plasma component contains high platelets and is separated and injected into joints or tendons. First, red and white cells are removed. Next, we remove the red cells as we know that these red cells break down cartilage and stimulate inflammation – an effect we don’t want.

Why do we want higher platelet concentrations? 

In general, different PRP or plasma systems yield different platelet concentrations. For example, some PRP systems have platelet concentrations above 1.5X the concentration in whole blood. However, other methods can produce an absolute blood platelet concentration greater than 5Xs. We don’t know whether higher platelet concentrations have a more significant effect, but recent evidence suggests that higher is better. 

Is a higher concentration or platelet count better? 

Some practitioners state that a higher concentration or platelet count is more effective than a lower one. However, the evidence for greater effectiveness is questionable. One study suggested that 10 billion platelets were required for better efficacy. However, this particular study is flawed. Until we have further studies, we recommend aiming for a higher platelet concentration and dose in a single or multiple injections. 

What is the difference between leucocyte-poor vs. leucocyte-rich PRP?  

Some PRP systems are a little more complicated and increase the concentration of platelets and white cells (leukocytes). Generally, these systems require more blood (50 mL) and repeated spins. Some of these systems include N-stride PRP.

Recent evidence suggests that leucocyte-poor is better for arthritis but leucocyte-rich for tendonitis. For example, a recent study found that leukocyte-poor PRP has fewer side effects but is as effective as leucocyte-rich PRP. Conversely, leucocyte-rich PRP is more effective in hip tendonitis or greater trochanteric syndrome.

How do PRP Injections Reduce Pain?

We don’t know the answer yet. However, many studies analyse the effects of PRP on cells and tissue in a lab. Platelets are essential cells that control clotting. They contain a high concentration of growth factors. These growth factors influence inflammation and healing. Injecting plasma therapy into a joint or tendon releases growth factors that improve the local environment. Ultimately, this leads to lower pain levels and faster tissue healing.

According to NIC, a UK body that assesses treatment, PRP reduces pain and may delay the need for a knee replacement.

Do Platelet-rich Plasma Injections Regenerate Cartilage or Tendon Tissue?

We don’t think so. There is no evidence that any plasma therapy injection can regenerate tissue. However, ongoing studies are looking at this question. Ultimately, the pain-killing effects of PRP are due to a better environment of the joint or tendon rather than tissue regeneration.

Is There Evidence for Platelet-rich Plasma Injections?

 Yes, but evidence exists for only a few common arthritis and tendonitis problems:

However, platelet-rich plasma has not shown effectiveness for other joints and tendons. 

You can read about the other effective treatments for arthritis and other injections for arthritis. Dr Masci published a paper summarising the PRP evidence in tendonitis, which is a good resource.

How Many PRP Injections Do You Need? 

We still need to determine the optimal number of PRP injections. However, for knee osteoarthritis, we recommend 2-3 injections every two weeks. For tendons, we recommend one to two injections two weeks apart.

However, second-generation PRP systems provide higher doses and concentrations per injection. One example is Arthrex ACP Max, a novel dual-syringe system that delivers 7-10 billion platelets per injection, requiring only one injection rather than 2-3 for standard PRP systems. 

What to Do Before PRP Therapy

Generally, we suggest PRP therapy works better if you follow the following guidelines:

  • Ensure you come in well-hydrated (drink at least a litre of water on the day of the injection).
  • Avoid medications that affect platelet function, such as aspirin or ibuprofen, at least two weeks before and for two weeks after a PRP injection.
  • Tell your doctor if you have any conditions that may affect the outcome of PRP, such as low platelet count, clotting disorders, or blood tumours.

Will Platelet-rich Plasma Injections Hurt?

platelet-rich plasma

Generally, no. Sometimes, the doctor will inject a local anaesthetic into the skin to stop the PRP injection from hurting. Also, PRP injections should be performed with ultrasound, which means they hurt less. Usually, a few people require painkillers after a PRP injection. Overall, we recommend taking paracetamol or codeine after the injection if needed. Also, we suggest applying ice packs every 4-6 hours, particularly after tendon injections.

What are the Potential Side Effects of Platelet-rich Plasma Injections? 

Generally, PRP therapy is safe. However, patients may experience joint or tendon soreness for up to a week. Typically, leucocyte-rich PRP elicits a more pronounced reaction after injection. Also, the positive effects do not start for at least 2-3 weeks after injection.

Overall, the risk of infection is lower than with other injections and is around 1 in 1500000 injections.

How Long Should You Rest after Platelet-rich Plasma Injections?  

Typically, it depends on whether a joint or tendon is injected.

For arthritis, we suggest resting from running or sports for a week. After a few days, you can start a non-impact activity such as swimming or cycling.

For tendons, we recommend a slightly more extended period of up to 2 weeks. For example, if you have an injection into a weight-bearing tendon, such as the Achilles, we suggest avoiding explosive activities (such as running) for 2 weeks.

How Long Do PRP Injections Last? 

The effect of PRP therapy can vary among patients. For arthritis, two or three injections can last 12-18 months. However, the impact on tendons is much more unpredictable.

What About Combined Injections: PRP and Hyaluronic Acid? 

Hyaluronic acid is a natural substance in cartilage, joints, and bone. Hyaluronic acid injections, like PRP, are used for knee arthritis and have shown promise. However, recent studies using PRP and hyaluronic acid combined have shown tremendous promise.

A recent study found that combining PRP with hyaluronic acid resulted in a greater effect at 3 and 12 months and fewer side effects than PRP alone.

Final word from Sportdoctorlondon about Platelet-rich Plasma Injections for Arthritis and Tendonitis  

PRP injections treat knee osteoarthritis, tennis elbow, plantar fasciitis, hip tendonitis, and shoulder tendonitis. However, there is no evidence for other joints or tendons. Generally, PRP therapy is more effective when combined with an exercise program under the guidance of an expert, such as a physiotherapist.

More injection information: