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Platelet-rich-plasma (PRP) injections in the knee

What is a PRP injection?

Platelet-rich plasma, or PRP, is a natural substance obtained from the person’s own blood. It has a high concentration of different growth factors that can help the healing process when injected into a joint or tendon. Plasma is one of the normal blood constituents and can be extracted by spinning the blood in a special machine at high speed (centrifuge) to separate its different components. The plasma naturally has a high concentration of platelets, which in turn are rich with growth factors. Research shows that these factors can assist in healing when injected into joints or tendons.

Are there different types of PRP preparations?

Yes, there are different types of PRP preparations. For example, some can concentrate platelets 8x their normal level, while others only double the platelets concentration. Generally, PRPs are divided into either “leukocyte-rich “ or “leukocyte-poor” preparations, according to the concentration of the white blood cells (leukocytes).

Determining which PRP injection to use to manage knee joint pain depends on the disease process affecting the joint. For example, in knee joint osteoarthritis, evidence shows good effects for “leukocytes-poor” preparations. However, “leukocyte-rich“ preparations are preferred for conditions like patellar tendonitis. More research is needed to establish stronger evidence regarding the different preparations of PRP and their role in managing knee joint pain.

This article provides an up-to-date summary regarding the role of PRP injections in the management of joints and tendons problems. Overall, there is good evidence supporting the use of PRP injections in managing knee osteoarthritis and tendon inflammation (tendonitis) like patellar tendinosis, golfers and tennis elbow, gluteal tendinosis/ greater trochanteric syndrome and plantar fasciitis.

What knee conditions would benefit from PRP injections?

Knee osteoarthritis

Most of the available evidence regarding PRP injections in managing arthritis shows a positive effect on the knee joint. More than 20 randomised controlled trials have demonstrated superior results for PRP vs other types of injections for knee joint arthritis.

Knee osteoarthritis is a degenerative condition that results from progressive wear and tear of the articular cartilage (the protective layer that covers the bones at the joint). It is the most common type of arthritis that affects the knee. When there is a significant loss of the articular cartilage, there is a loss of the normally smooth and frictionless movements at the joint and bones start rubbing against each other. This results in joint inflammation, which usually manifests as joint pain and swelling. To find out more, read our article about knee joint osteoarthritis. The available injection treatment options for osteoarthritis include corticosteroid injections, hyaluronic acid injections and Platelets-rich plasma (PRP) injections. PRP injections are being increasingly used in the management of knee osteoarthritis.

Patellar tendinosis

Patellar tendinosis is usually an overuse injury of the patellar tendon. This tendon connects the patella (knee cap) to the upper part of the tibia (the shin bone). PRP injection is a good treatment option for tendinosis in general and is well-used in treating patellar tendinosis. PRP has been clinically proven to enhance the healing process and recovery of tendons, and it has been shown to be a safe treatment option for patellar tendinosis. It is usually reserved for cases that do not respond to all other treatment options. Evidence suggests that a series of three injections a few weeks apart (rather than a single injection) is required to treat the tendinopathy effectively. To learn more about this condition, please read our article about patellar tendinosis.

Pes anserine tendinosis

Evidence supports the use of PRP injections in managing pes anserine tendinosis when the condition is not responding to conservative management and steroid injections. Please read our article about pes anserine tendinosis/bursitis to learn more about this condition.

Do PRP injections reverse knee joint damage?

Although the injected plasma is rich in growth factors and can promote healing, there is no convincing evidence that PRP injections can reverse damage to the articular cartilage. Further studies are needed to establish whether PRP injections have a regenerative effect when injected into joints and tendons.

What shall I do before a PRP injection?

Make sure you are well-hydrated before attending your appointment. Also, it is important to avoid anti-platelet medications (like aspirin and ibuprofen) as these reduce the efficiency of platelets and interfere with their function. Therefore, you should avoid such medicines for 10-14 days before the procedure. Similarly, you should avoid these medicines for a few weeks following the procedure.

How many PRP injections do I need?

Currently, the evidence suggests that a course of treatment is more effective than a single injection for managing arthritis or tendinosis. Still, more research is needed to strengthen this. The current results show that a course of 2 or 3 injections provides a longer response, lasting up to 24 months after the injection, compared to a single injection. The treatment course we recommend for managing knee joint osteoarthritis usually consists of 3 injections two weeks apart.

Is ultrasound needed to perform platelet-rich plasma injections for the knee?

Yes. Although an intra-articular injection of the knee joint can be done without image guidance by an experienced doctor, the accuracy is only 80% at best (approx. 20% of these unguided injections would miss the targeted area). Image-guided knee injections can be done using fluoroscopy (x-ray) or ultrasound guidance. The latter is preferred as it is more accurate, usually less painful and lacks any ionising radiation exposure.

What are the possible side effects of a PRP injection for the knee?

  • As with other injections, there is a minimal risk of infection (approx. 1:10000 to 1:100000).

  • There is also the possibility of a pain flare for a few weeks following the injections. You can use simple painkillers like paracetamol and codeine but avoid using medicines like Ibuprofen and Voltarol, as these can interfere with the platelets' function.

  • The possibility of tendon injury/rupture is rare and only applicable to PRP injections performed into tendons (like the patellar tendon of the knee).

  • Rarely, in about 1-2% of cases, the symptoms can worsen after the injection.

  • I will discuss the treatment and the potential risks before the procedure.

What do I need to do after the procedure?

You will be advised to rest and avoid strenuous activities to the body area injected (for example, your knee joint) for at least one week after the injection. The advised rest period may vary depending on the area treated. Also, monitor the area for any redness, swelling, pain or warmth. These are potential signs of infection that are extremely rare (1:10000-1:100000) but require urgent medical attention.

How soon will I notice improvement after a PRP injection?

The PRP injection is a long-term therapy, meaning it usually takes a few weeks after the procedure for the patient to start noticing the benefits. Also, the response to the treatment will depend on the specific condition being treated. For example, for knee joint osteoarthritis, the positive effect of the PRP injection can last for more than a year.

Could both PRP and hyaluronic acid be combined in one injection?

Hyaluronic acid is a naturally occurring substance found in joints, tendons and connective tissues. Please read our article about Hyaluronic acid injection to learn more about this treatment option. A study looking into combining PRP and hyaluronic acid injections has shown less pain in the combined treatment group at 3 and 12 months compared to PRP injection. However, research is still scarce, and more is needed to help us build more robust conclusions. Generally, we advise separating these treatment options.

Is PRP injection for the knee better than corticosteroid?

A recent systematic review and meta-analysis showed that PRP treatment has superior results to cortisone for managing moderate knee joint osteoarthritis. The positive results from the PRP injections were double those observed from the corticosteroid treatment. Furthermore, the effect lasted longer, as significant results secondary to the PRP treatment were observed 6-9 months after. PRP therapy is not found to cause harm, unlike corticosteroids, as some research has shown potential adverse effects on the articular cartilage, especially with repeated injections.

Can I have a PRP injection if I am on blood thinners like Warfarin?

Yes. Warfarin does not affect PRP treatment. However, there is a small risk of increased bleeding following the procedure if you are on warfarin or other blood-thinning medicines. I will discuss this before the procedure.


PRP injections are becoming an established treatment for managing patients with knee joint osteoarthritis. We use leukocytes poor (low white blood cell PRP preparation) for treating knee joint osteoarthritis and advise combining this with an exercise and physiotherapy program for best results.


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Specialist Consultant Musculoskeletal Radiologist Doctor with extensive experience in image-guided intervention

To book a consultation:

Call us on 020 3442 1259 or Book online

The Musculoskeletal Ultrasound & Injections clinic

Healthshare West London (The Riverside) Clinic
Unit 3, Brentside Executive Park

Brentford, TW8 9DR

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