The most common cause of arthritis in the knee is osteoarthritis. The progressive wearing of the cartilage characterises this condition. As the cartilage is worn away, bone on bone is exposed, leading to inflammation, pain, and swelling. Overall, lifestyle factors are the most effective treatments for osteoarthritis, including exercise, weight loss, and 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 knee has been becoming popular. Find out what a PRP injection for knee is about, including answers to commonly asked questions:

What is PRP?

Platelet-rich plasma injections - alternative to cortisone injection in shoulder

 

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

There are different PRP systems. Which one is best? 

Not all PRP therapy systems are precisely the same. For example, some systems concentrate platelets up to 8x normal blood. Other methods only concentrate up to 2x. Also, the white cells’ concentration can change depending on the spin’s speed.

So, what is the best type of PRP therapy for knees? Well, it depends on the disease process injected. Generally, we think that for knee arthritis, we need a platelet concentration of up to 3x without the white cells. However, we believe having a slightly higher concentration of platelets with a higher concentration of white cells is better for tendons. But, we still need to do more studies.

This blog outlines the current evidence for PRP in joints and tendons. Overall, the best proof of PRP is in knee arthritis. Twenty-three randomised trials show that PRP is better than other injections for knee arthritis. In addition, there is some evidence for PRP treatment in treating 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.

One study published in 2021 said that a 10 billion platelet dose is optimal. But this study is fundamentally flawed. 

Another study published in 2024 showed that a one-off higher dose of platelets approaching 5 billion was better than 2.5 billion platelets. This study also had limitations, being short-term (6 months) and having low subject numbers with low-grade arthritis. 

Other studies show the opposite – higher platelet doses lead to a less effective result on pain and function.

We don’t know the optimal platelet count for knee arthritis, but we think doctors should aim for a platelet dose approaching 4-5 billion. This dose can be achieved with one or multiple doses over 203 injections. 

Does PRP injection for 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 done to see if PRP treatment has an actual regenerative effect.

Do I need to prepare for a platelet-rich plasma injection for knee?

Usually, we ask you to be well hydrated. We suggest you drink 1 to 1.5 litres of water on the day of the PRP injeciton.

Also, you must avoid medications that affect platelets, such as aspirin or ibuprofen, for at least ten days before the injection. In addition, you should avoid these same medications for a few weeks after the last injection.

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 suggest 2-3 injections about two weeks apart for the best effect of PRP therapy. Generally, 2-3 injections are better than one as they can last 24 months.

Are ultrasound-guided injections better for platelet-rich plasma injections for knee? 

Yes. Even with experienced hands, the accuracy of a knee joint injection only approaches 80%. So, for knee injections, 1 in 4  without imaging misses the target. There are two ways to do image-guided injections: ultrasound or X-ray. We think ultrasound is much better as it’s cheaper and doesn’t expose the person to harmful radiation.

How long do I need to rest after a plasma injection for my knee? 

We suggest you avoid exercising the joint for at least a week after the platelet-rich plasma injection for knee. 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 less than 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 could sometimes worsen your problem; luckily, this only occurs in 1-2% of cases. It would be best to speak to 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 usually settles after 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, for knee arthritis, we think the impact of platelet-rich plasma injection lasts for 12-18 months.

How expensive are PRP injections for knees? 

Costs of PRP treatment can vary from £300 to £2000 per injection. However, the more expensive PRP injections are not necessarily better. For example, N Stride PRP, known as tSupermanman PRP, requires one injection but costs £2000. However, studies on N Stride show very little difference compared to other PRP systems. So generally, you should not equate price to better effect.

Could you combine both PRP and hyaluronic acid?

Hyaluronic acid is a natural substance found in bones, joints, and tendons. Injecting hyaluronic acid into knee arthritis improves pain and function, but it’s not as good as PRP. However, recent studies suggest combining the two might be better than either alone. In addition, there is reduced pain at 3 and 12 months in the combined treatment. So, overall, we await further studies before making a specific recommendation.

Is PRP injection for knee better than cortisone?

Recent evidence suggests that PRP treatment is better than cortisone. This positive effect is most significant between 6 and 9 months in people with moderate and moderate arthritis. In addition, the effect is double the positive effect of cortisone. Also, PRP therapy is not considered harmful, unlike cortisone, which shows some potential adverse effects on cartilage.

Are stem cells better than platelet-rich plasma injection for knee? 

stem cell injections

Stem cells are obtained from fat or bone marrow. These cells are not actual stem cells but are called pericytes. We think that these cells might be able to improve the environment of a joint or tendon a little better than PRP. However, a recent review suggests there is little evidence stem cells are worth the expense. Also, a study comparing stem cells with PRP in knee arthritis showed no difference between groups. So, overall, we still need more evidence before saying that stem cells are better than PRP for knee arthritis.

Other frequently asked questions about PRP in knees

Do I need to prepare for my PRP injection?

Yes. We suggest 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 common after 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 knee

Regenerative medicine is a new field and becoming more popular. We take a common sense but cautious approach to using PRP treatment in 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.

Related topics:

Dr. Masci is a specialist sport doctor in London. 

He specialises in muscle, tendon and joint injuries.