The most common cause of arthritis in the knee is osteoarthritis. The progressive wearing of the cartilage characterises this condition. As the cartilage wears away, bone-on-bone contact is exposed, leading to inflammation, pain, and swelling. Overall, lifestyle factors are the most effective treatments for osteoarthritis, including regular exercise, maintaining a healthy weight, and a balanced diet. However, cortisone injections have a limited effect and might cause harm. Moreover, surgery is considered a last resort. Recently, platelet-rich plasma injection for the knee has become popular. Find out what a PRP injection for knee arthritis is about, including answers to commonly asked questions.  

What is PRP?

Platelet-rich plasma, or PRP, is obtained from whole blood. The plasma contains a high concentration of platelets. Platelets release numerous growth factors upon injection into the target joint or tendon.

There are Different PRP systems. Which one is best?

Not all PRP therapy systems are identical. For example, some systems concentrate platelets up to eight times the normal blood level. Other methods achieve only a 2x concentration. Additionally, white blood cell concentration can vary with the spin rate.

What is the most effective type of PRP therapy for knees? Well, it depends on the disease process being injected. Generally, we believe that for knee arthritis, a platelet concentration of up to 3 times is required without the inclusion of white blood cells. However, we think that having a slightly higher platelet concentration, along with a higher white blood cell concentration, is better for tendons. But we still need to do more studies.

This blog outlines the current evidence for the use of PRP in joints and tendons. Overall, the most compelling evidence of PRP is in the treatment of knee arthritis. Twenty-three randomised trials show that PRP is better than other injections for knee arthritis. Additionally, there is evidence supporting the use of PRP for conditions such as tennis elbow, plantar fasciitis, greater trochanteric syndrome, and rotator cuff tendonitis.

What is the optimal dose of platelets in PRP?

We don’t know yet.

A 2021 study reported that a 10 billion platelet dose is optimal. But this study is fundamentally flawed.

Another study, published in 2024, showed that a one-time higher dose of platelets, approaching 5 billion, was more effective than 2.5 billion platelets. This study also had limitations, including its short-term nature (6 months) and the small number of subjects with low-grade arthritis.

We don’t know the optimal platelet count for knee arthritis, but doctors should aim for a platelet dose approaching 4-5 billion. This dose can be achieved with one or multiple doses, typically administered over 2-3 injections. However, second-generation PRP injections are now available, delivering a higher platelet dose and concentration. One example is Arthrex ACP Max, which gives 7-10 billion platelets per injection. 

Does PRP injection for the knee reverse joint damage?

Generally, we think it does not. However, we know that the plasma growth factors change the joint or tendon environment. However, more studies are being conducted to determine whether PRP treatment has regenerative effects.

Do I Need to Prepare for a Platelet-rich Plasma Injection for the Knee?

We usually recommend that you remain well hydrated. We recommend drinking 1-1.5 litres of water on the day of PRP injection.

Additionally, avoid medications that affect platelet function, such as aspirin or ibuprofen, for at least 10 days before the injection. Additionally, you should avoid these medications for a few weeks after the last injection.

This blog provides a more detailed overview of PRP preparation. 

How many PRP Injections do I need for Knee Arthritis? 

Overall, we still don’t know the answer to this question. However, for knee arthritis, we recommend three PRP injections approximately two weeks apart to optimise effectiveness. Generally, two to three injections are preferable to a single injection, as they can last up to 24 months.

Are Ultrasound-guided Injections better for Platelet-rich plasma (PRP) Injections in the Knee? 

Yes. Even with experienced hands, the accuracy of a knee joint injection only approaches 80%. For knee injections, 1 in 4 without imaging misses the target. There are two primary methods for performing image-guided injections: ultrasound and X-ray. We believe ultrasound is a better option, as it’s less expensive and doesn’t expose the person to harmful radiation. 

How long do I need to rest after a Plasma Injection for my Knee? 

We recommend avoiding joint exercise for at least 1 week after knee platelet-rich plasma injection. This rest time may vary depending on the joint or structure injected.

Platelet-rich Plasma Injection for Knee  Side Effects

Unfortunately, any procedure has risks. Luckily, we only use your blood, so the risks are lower than those associated with cortisone injections. Nevertheless, there are risks of infection (1/10000), pain flare, and rupture (rare). A flare of pain is typical and can last for a few weeks. We suggest regular ice packs and paracetamol/codeine for a short period after the injection. An injection can sometimes worsen your problem; fortunately, this occurs in only 1-2% of cases. It is best to consult your doctor about these potential risks.

Knee pain after PRP injection: How common is it? 

A flare after a PRP injection for knee arthritis is common. However, the flare typically resolves within 1-2 weeks. Also, we know that leukocyte-poor PRP produces less knee pain after a PRP injection than leukocyte-rich PRP.

How long does the Positive Effect Last? 

Generally, the positive effect depends on the disease. For example, in knee arthritis, we estimate that the effect of platelet-rich plasma injection lasts 12-18 months.

How Expensive are PRP injections for Knees? 

The costs of PRP treatment can range from £300 to £ 2,000 per injection. However, the more expensive PRP injections are not necessarily better. For example, N Stride PRP requires one injection but costs £2,000. However, studies on N Stridehave shown very little difference relative to other PRP systems. Generally, you should not equate price with better effect.

Dr Masci offers higher concentration PRP Arthrex ACP Max for £1350. 

Could you combine both PRP and Hyaluronic acid?

Hyaluronic acid is a natural substance found in bones, joints, and tendons. Injecting hyaluronic acid into the Knee for arthritis improves pain and function, but it is less effective than platelet-rich plasma (PRP). However, recent studies suggest that combining the two might be more effective than using either alone. Additionally, pain reduction is observed at both 3 and 12 months in the combined treatment. So, overall, we await further studies before making a specific recommendation.

Is PRP injection for the Knee better than Cortisone?

Recent evidence suggests that PRP treatment is superior to Cortisone. This positive effect is most pronounced between 6 and 9 months in individuals with moderate-to-severe arthritis. In addition, the effect is twice that of Cortisone. Additionally, PRP therapy is not considered harmful, unlike Cortisone, which has been shown to have some potential adverse effects on cartilage.

Are Stem Cells More Effective than Platelet-rich Plasma Injection for the Knee? 

Stem cells are obtained from fat or bone marrow. These cells are not stem cells; they are pericytes. We believe that these cells may be able to slightly enhance the environment of a joint or tendon compared with PRP. However, a recent review suggests that there is little evidence to support the cost-effectiveness of stem cells. Additionally, a study comparing stem cells with PRP in knee arthritis found no difference between the groups. Overall, we still need more evidence before concluding that stem cells are superior to PRP for knee arthritis.

Other Frequently Asked Questions about PRP in the Knees

Do I need to prepare for my PRP injection?

Yes. We suggest that you are well hydrated on the day of the injection. Generally, you should drink 1-1.5 litres of fluid. Also, avoid medication such as aspirin or Ibuprofen for at least ten days before the procedure.

Can I have PRP if I’m on a blood thinner such as Warfarin? 

Yes. Warfarin does not affect PRP. However, you must tell your doctor you are on Warfarin as you have an increased risk of bleeding after the procedure.

How common is knee pain after PRP injection? 

Knee pain is a common side effect of a PRP injection. Generally, pain lasts for a few days to a few weeks. However, we know that PRP with a high concentration of white cells increases the risk of a flare.

Final word from Sportdoctorlondon about Platelet-rich Plasma Injection for the Knee

Regenerative medicine is a relatively new field that is gaining popularity. We adopt a common-sense yet cautious approach to utilising PRP treatment in our practice. We currently use low white cell PRP therapy for knee arthritis combined with exercise. However, we are reluctant to use PRP for other joints until there is more evidence.

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