Platelet-rich plasma (PRP) injections use a concentrated portion of your own blood to try to ease the pain of knee osteoarthritis. The concentrate is rich in platelets, which contain growth factors, and is injected directly into your knee.
The evidence is mixed. Several trials and reviews have found that PRP improves pain and function in early to moderate osteoarthritis, [2] [3] but a large Melbourne trial found no benefit over a placebo injection. [5] PRP does not reverse arthritis, and it is unlikely to help advanced arthritis.
At a Glance
- PRP is prepared from your own blood and injected into your knee.
- Some trials and reviews report better pain and function than other injections in early to moderate knee osteoarthritis.
- A 2021 Melbourne trial of 288 people found no meaningful benefit over a salt-water placebo injection at 12 months.
- PRP does not turn an arthritic knee back to normal and is unlikely to help advanced, bone-on-bone arthritis.
- Weight loss, exercise and physiotherapy have stronger evidence and should be tried first.
On this page
- What is PRP?
- What is PRP used for?
- How does PRP work?
- How is PRP prepared?
- How long does PRP last in the knee?
- How many PRP injections are needed for knee osteoarthritis?
- Can PRP regenerate cartilage?
- Does PRP actually work for knee osteoarthritis?
- How does PRP compare with hyaluronic acid injections?
- Can you walk after a PRP injection into the knee?
- How fast does PRP work?
- What are the side effects of a PRP injection into the knee?
- Who is likely to benefit from PRP?
- Summary
- References
What is PRP?
PRP stands for platelet-rich plasma. Blood has three main components: blood cells (red and white), platelets and plasma, the liquid part. PRP is a concentrated form of platelets, which contain growth factors involved in healing.
What is PRP used for?
PRP is used to try to ease the symptoms of knee osteoarthritis. It is also used for some long-standing tendon problems, such as patellar tendinopathy.
How does PRP work?
PRP is rich in growth factors. In laboratory studies, these growth factors attract stem cells, encourage new blood vessels to form and reduce inflammation. PRP may also stimulate cartilage cells, but laboratory findings do not always translate into benefits for patients.
How is PRP prepared?
There are many ways of preparing PRP, but they share four basic steps:
- Blood draw: 30–60 mL of blood is taken from your arm.
- Centrifugation: the blood is spun in a centrifuge, which separates the red blood cells, white blood cells, platelets and plasma by weight.
- Activation: chemicals may be added to make the platelets release their stored growth factors.
- Injection: the PRP is injected into your knee joint.
Preparation varies between clinicians and laboratories. Differences in spin time, spin speed and activation method mean that the amount of growth factors can differ, even though the basic steps are the same.
How long does PRP last in the knee?
In trials of PRP for early osteoarthritis, improvements in pain and function were reported for up to 6–12 months. [2] Results vary, and some people notice little or no benefit.
How many PRP injections are needed for knee osteoarthritis?
There is no agreed number. One randomised trial in early knee osteoarthritis found that three injections of PRP, given at intervals, led to larger improvements in pain and function at six months than a single injection. [1] Treatment protocols still vary between clinicians.
Can PRP regenerate cartilage?
Laboratory studies suggest that PRP can influence the repair of damaged cartilage, by encouraging stem cells to move to the damaged area, multiply and change into cartilage cells. PRP may also reduce inflammation in the lining of the knee joint (the synovium), where pain receptors are found.
In patients, however, PRP has not been shown to rebuild cartilage. In the Melbourne trial, PRP did not change the volume of knee cartilage compared with a placebo injection. [5] PRP does not turn an arthritic knee back to normal.
Does PRP actually work for knee osteoarthritis?
The evidence is mixed. A review that combined 14 randomised controlled trials in early to moderate knee osteoarthritis found that PRP improved pain and function more than other injections, such as steroids, hyaluronic acid and salt water. [2] Another review of randomised trials reached a similar conclusion. [3]
However, many of these trials were small. The RESTORE trial in Melbourne randomised 288 people with mild to moderate knee osteoarthritis to PRP or a salt-water placebo injection. At 12 months, there was no meaningful difference in knee pain or cartilage volume between the two groups. [5]
How does PRP compare with hyaluronic acid injections?
Viscosupplementation involves injecting hyaluronic acid into the knee. Hyaluronic acid is normally produced by the lining of the knee joint and acts as a lubricant. Synvisc and Durolane are brand names of hyaluronic acid injections.
One review found that PRP and hyaluronic acid had similar effects at six months, but PRP gave better function scores at 12 months, suggesting its effect may last longer. [3]
However, a well-designed trial that followed patients for five years found no advantage of PRP over hyaluronic acid. [4]
Can you walk after a PRP injection into the knee?
Yes. There are no restrictions on putting weight through your leg after a PRP injection. You may have some minor discomfort immediately afterwards, but this should not stop you from walking.
How fast does PRP work?
The effects of a PRP injection are not immediate. If PRP helps, any improvement usually develops gradually over the following weeks and months.
What are the side effects of a PRP injection into the knee?
The risks of a PRP injection are small. They include infection, pain at the injection site and, rarely, an allergic reaction or a local blood clot.
Who is likely to benefit from PRP?
People with early arthritis and no other structural problems in the knee, such as a large unstable meniscal tear, are the most likely to benefit. In advanced, bone-on-bone arthritis, PRP is unlikely to help because the damage to the joint is too advanced.
Other non-surgical treatments, including weight loss, physiotherapy and anti-inflammatory medicines, have stronger evidence and should be tried first. You can read about them in Non-surgical options for knee osteoarthritis.
It is important to have your knee assessed before starting PRP, to see whether it is a reasonable option for you. PRP injections do not attract a Medicare rebate and usually involve an out-of-pocket cost. If your arthritis is advanced, other treatments, including surgery, may be more appropriate.
Summary
PRP may ease pain and improve function for some people with early to moderate knee osteoarthritis, but the evidence is mixed, and a large Melbourne trial found no benefit over a placebo injection. PRP does not reverse arthritis and has little role in advanced arthritis. Weight loss, exercise and physiotherapy should be tried first.
If you would like to discuss how this applies to your knee, you can book a consultation with Dr Vishal Pai.
References
Show all 5 referencesHide references
- Görmeli G et al. 2017. Multiple PRP injections are more effective than single injections and hyaluronic acid in knees with early osteoarthritis: a randomized, double-blind, placebo-controlled trial. Knee Surgery, Sports Traumatology, Arthroscopy.
- Shen L et al. 2017. The temporal effect of platelet-rich plasma on pain and physical function in the treatment of knee osteoarthritis: systematic review and meta-analysis of randomized controlled trials. Journal of Orthopaedic Surgery and Research.
- Dai WL et al. 2017. Efficacy of platelet-rich plasma in the treatment of knee osteoarthritis: a meta-analysis of randomized controlled trials. Arthroscopy.
- Di Martino A et al. 2019. Platelet-rich plasma versus hyaluronic acid injections for the treatment of knee osteoarthritis: results at 5 years of a double-blind, randomized controlled trial. The American Journal of Sports Medicine.
- Bennell KL et al. 2021. Effect of intra-articular platelet-rich plasma vs placebo injection on pain and medial tibial cartilage volume in patients with knee osteoarthritis: the RESTORE randomized clinical trial. JAMA.
Find out which treatments may suit your knee
Dr Vishal Pai assesses knee osteoarthritis and can advise whether PRP, other non-surgical treatments or surgery may suit you. You can arrange a consultation to discuss your symptoms and options.
Written by Dr Vishal Pai
Vishal is an experienced knee surgeon based in Bayside, Melbourne. He consults at Sandringham Orthopaedic Specialists and operates at The Avenue Hospital and Calvary Holmesglen Private Hospital. His practice focuses on sports knee surgery, including ACL reconstruction and meniscal repair, as well as robotic knee replacement.