The most common cause of arthritis in the knee is osteoarthritis. This condition is characterised by the progressive wearing of the cartilage. 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. Cortisone injections have a limited effect and might cause harm. Moreover, surgery is considered a last resort. Recently, platelet-rich plasma or PRP injections in knees are becoming popular. Find out what PRP injections in the knees are about including answers to commonly asked questions:

What is PRP?

Platelet-rich plasma injections

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

There are different PRP systems: Which one is best? 

Not all PRP systems are exactly the same. Some systems concentrate platelets up to 8x normal blood. Other systems only concentrate up to 2x. Also, depending on the speed of the spin, the concentration of the white cells can also be changed.

So, what is the best type of PRP? 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, for tendons, we believe that having a slightly higher concentration of platelets with a higher concentration of white cells is better. But, we still need to do more studies.

This blog outlines the current evidence for PRP in joints and tendons. Overall, the best evidence for PRP is in knee arthritis. There are 23 randomised trials that show that PRP is better than other injections for knee arthritis. There is some evidence for PRP injections in treating tennis elbow, plantar fasciitis, and greater trochanteric syndrome.

Do PRP injections for knees reverse joint damage? 

Generally, we think it does not. However, we know that the growth factors in the plasma change the environment of the joint or tendon. However, more studies are being done to see if PRP has a true regenerative effect.

Do I need to prepare for PRP injections for knees?

Usually, we ask you to be well hydrated. Also, it is important you avoid medications that affect platelets such as aspirin or ibuprofen for at least 10 days prior to the injection. Also, you should avoid these same medications for a few weeks after the last treatment.

How many injections do I need? 

Overall, we still don’t know the answer to this question. For knee arthritis, we suggest 2-3 injections about 2 weeks apart for the best effect. For tendons, we recommend 1-2 injections about 2 weeks apart. However, some new PRP systems with higher concentrations of platelets and white cells might mean that only one injection is needed.

Are ultrasound-guided injections better? 

injection for arthritis in knees

Yes. Even with experienced hands, the accuracy of a knee joint injection only approaches 80%. For hip inSo, 1 in 4 injections done 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 an injection? 

In general, we suggest you avoid exercising the joint or tendon for at least a week after the injection. This rest time may vary depending on the structure injected.

What are the risks? 

Unfortunately, any procedure has risks. Luckily, we are only using your blood so risks are less compared to other injections such as cortisone. Nevertheless, there are risks of infection (1/10000), pain flare, and rupture (very rare). A flare of pain is common and can last for a few weeks. We suggest regular ice packs and paracetamol/codeine for a short period after the injection. In some cases, an injection could make your problem worse; luckily this only occurs in 1-2% of cases. You should speak to your doctor about these potential risks.

How long does the positive effect last? 

Generally, the positive effect depends on the disease. For knee arthritis, we think the effect lasts for 12 months. For tendons, evidence suggests that a positive effect remains for at least 2 years.

How expensive are PRP injections for knees? 

Costs of PRP can vary from £300 to £2000 per injection. However, the more expensive PRPs are not necessarily better. For example, N Stride PRP, known as the superman PRP, requires one injection but costs up to £2000. However, studies on N Stride show very little difference compared to other PRP systems. 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 that combining the two might be better than one alone. So, overall, we await further studies before making a specific recommendation.

Are PRP injections better than cortisone?

Recent evidence suggests that PRP is better than cortisone. Also, unlike cortisone, which shows some potential negative effects on cartilage, PRP is not thought to be harmful.

Are stem cells better than PRP injections for knees? 

stem cell injections

Stem cells are obtained from fat or bone marrow. These cells are not true stem cells but 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. Overall, we still need more evidence before we can say that stem cells are better than PRP for arthritis.

Final word from Sportdoctorlondon

Regenerative medicine is a new field and becoming more popular. We take a common sense but cautious approach to using these injections in practice. We currently use low white cell PRP for knee arthritis combined with exercise. In addition, we are starting to use PRP in tennis elbow, plantar fasciitis, and greater trochanteric syndrome (hip tendonitis). However, we are reluctant to use PRP for other joints and tendons until there is more evidence.

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Dr. Masci is a specialist sport doctor in London. 

He specialises in muscle, tendon and joint injuries.

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