PRP Shots For Knee Arthritis – Are They Effective?

PRP Needle

PRP (platelet-rich-plasma) therapy has been gaining popularity recently owing to its promise in a number of areas such as hair regeneration, wound healing, skin rejuvenation, and slowing the progression of arthritis. A variety of high-profile athletes have also touted the benefits of PRP for the knee joint. Many claim the shots have helped them during their recovery from sport-related injury. Currently, over 80,000 athletes are treated with PRP every year.1 

Despite its growing usage, PRP’s therapeutic effect on muscle and bone-related injuries is not clear. If you are considering PRP shots for knee arthritis understand that this area has received limited attention by scientists. Therefore, it is difficult to predict how successful this treatment will be. Commercial PRP therapy clinics exhibit tremendous variability in their claims of PRP’s effectiveness (40-100%)2 in treating knee arthritis. Before committing to any invasive medical procedure, ensure that you are fully educated on the matter and have consulted your doctor. 

What is Platelet Rich Plasma (PRP)?

Your blood has four primary components: red blood cells, white blood cells, plasma, and platelets. PRP refers to a mixture of plasma and platelets isolated from the other aforementioned blood components. 


Plasma is a clear yellowish substance that composes 55% of your blood’s total volume. Despite being 95% water it contains a number of important substances such as electrolytes, proteins, and hormones. Think of it as the “liquid” portion of your blood.   

blood components after being centrifuged
Blood after being centrifuged. The yellowish liquid is the platelet-rich plasma (PRP).

Platelets (Thrombocytes) 

Ever had a papercut? Piercing the skin damages blood vessels and causes external bleeding. Fortunately, the bleeding eventually slows and then completely stops. We can thank our platelets for this. We have about 150,000 to 450,000 of them in every milliliter of our blood. These tiny cell fragments drive a process called coagulation. At sites of trauma, blood typically clots and turns into a semi-solid state; halting any bleeding. 

Individuals with a low platelet count are at a higher risk of excessive bleeding because they do not have enough platelets to cause the blood to coagulate around sites of trauma. While platelet’s primary role is blood clotting, they have secondary functions that can be leveraged to speed up tissue repair. Platelets contain a number of growth factors and signaling molecules. These substances can increase stem cell activity, blood supply and the growth of new cells.3 Put simply, the rationale for PRP therapy is that injecting a concentrated dose of these platelets into damaged tissue will trick the body into increasing the number of molecules that promote healing in the area. 

How do PRP Injections for Knee Arthritis Work? 

Knee arthritis affecting the left tibiofemoral compartment
Knee arthritis affecting the medial (inside) tibiofemoral compartment

Using a syringe, a physician withdraws approximately 60ml of your blood. It is then placed into a centrifuge. These devices spin at extremely high speeds generating high centrifugal forces. As a result, the blood separates with denser elements sinking to the bottom of the container. Once fully separated, the plasma and platelet components can be isolated into a solution (PRP). Approximately 2-6ml of PRP is then injected deep into the knee joint as close to the arthritic area as possible.3 

How Much Pain Relief can PRP Injections Provide?

Unfortunately, many scientists are still asking this question. Research examining the effect of PRP on knee arthritis is still fairly young. Thus drawing a firm conclusion regarding the benefits of PRP for knee arthritis remains challenging because: 

  • The number of studies examining the effect and time-course of PRP treatment are limited.4
  • Comparing PRP studies is challenging because there are a variety of types of PRP formulas used in the research.5
  • Some recent research shows that PRP does not outperform placebo injections.6

A study published in collaboration with Osteoarthritis Research Society International (OARSI) in 2019 compared the effects of PRP to a placebo injection of saline solution. After the injections, they followed patients for 24 weeks and assessed changes in knee arthritis symptoms along the way. Participants rated their knee pain on a ten-point scale. During the study period, those who received the placebo injection improved on average by 3.5 points. (figure 1a). Those who were administered with the PRP injection had a slightly inferior improvement of 2.9 points (figure 1a). Despite continued improvement for the PRP group at week 12 (figure 1b), by week 24, both the placebo and PRP groups reported similar levels of knee pain.

Graphs showing that placebo injections are equivalent in effectiveness to PRP
Figure 1: (a) Average decrease in pain of participants in the study shown on a 10-point scale (b) Fluctuation in symptoms over a 24 week period.

In contrast, a 2019 study published by the Journal of Arthroscopic Surgery found that PRP outperformed placebo injections.7 At 12 months patients who had received the PRP injection reported on average, a 21% increase in their overall knee function. While the knee function in those who received the placebo treatment remained unchanged. 

While there is potential that PRP may one day become a standard knee arthritis treatment, it will take time for the evidence to accumulate. As such, major medical authorities in the treatment of knee arthritis do not currently recommend the use of PRP for knee arthritis:

  • Osteoarthritis Research Society International (OARSI): We strongly recommended against the use of PRP because the evidence in support of these treatments is of extremely low quality, and the formulations themselves have not yet been standardized.” 8

It is possible PRP may provide you with pain relief, however, research into PRP shots for knee arthritis is still young. It is currently unclear how much pain relief this treatment can provide.

How Much do PRP Injections Cost?

In 2018, the average cost for a PRP shot for knee arthritis was $744.00.10 Depending on your region it is common for the cost of treatment to differ by $150.00.10 In comparison, a single injection of Hyaluronic Acid (HA) costs approximately $400.00-800.00.11 Keep in mind that these are the costs for a single injection. If PRP is effective for you – more injections may be required to sustain any benefits. It is not uncommon to require up to three PRP injections within a six months time frame which could cost more than $2000.00.13 If you respond well to a course of PRP treatment, you may experience relief from symptoms for up to a year.13 

Are PRP Shots for Knee Arthritis Safe? 

PRP shots for knee arthritis are relatively safe with no serious complications reported.11 However, patients should expect some moderate pain and swelling immediately after receiving the injection. Discomfort around the knee joint typically resolves in several days.11

What are the Alternatives to PRP therapy? 

PRP shots for knee arthritis are attractive to many because they are perceived as a natural and low-risk treatment. In contrast, corticosteroids – another popular injection have the opposite reputation. If you want to avoid surgery and the side-effects of anti-inflammatory painkilling drugs here are several viable options:

Elderly Woman Exercising
  • Experts unanimously recommend exercise for patients suffering from knee arthritis. While exercise can provide tremendous benefit, performing the wrong type of exercise could be counter-productive. Check out this free guide to exercises for knee arthritis. Here you’ll learn the most effective types of exercise and be able to access free exercise programs designed for different stages of the disease. 

Additional Resources


  1. Wasterlain, A. S., Braun, H. J., Harris, A. H., Kim, H. J., & Dragoo, J. L. (2013). The systemic effects of platelet-rich plasma injection. The American journal of sports medicine, 41(1), 186-193.
  2. Piuzzi, N. S., Ng, M., Kantor, A., Ng, K., Kha, S., Mont, M. A., & Muschler, G. F. (2018). What is the price and claimed efficacy of platelet-rich plasma injections for the treatment of knee osteoarthritis in the united states?. The journal of knee surgery.
  3. Alves, R., & Grimalt, R. (2018). A review of platelet-rich plasma: history, biology, mechanism of action, and classification. Skin appendage disorders, 4(1), 18-24.
  4. Han, Y. H., Huang, H. T., Pan, J. K., Lin, J. T., Zeng, L. F., Liang, G. H., … & Liu, J. (2018). Comparison of platelet-rich plasma vs hyaluronic acid injections in patients with knee osteoarthritis: a protocol for a systematic review and meta-analysis. Medicine, 97(44).
  5. O’Connell, B., Wragg, N. M., & Wilson, S. L. (2019). The use of PRP injections in the management of knee osteoarthritis. Cell and tissue research, 376(2), 143-152.
  6. Dório, M., Pereira, R. M., Oliveira, R. M., Luz, A. G., & Fuller, R. (2019). Platelet-rich plasma and plasma for treatment of knee osteoarthritis: a double-blind placebo-controlled randomized clinical trial. Osteoarthritis and Cartilage, 27, S481–S482. doi:10.1016/j.joca.2019.02.531 
  7. Lin, K. Y., Yang, C. C., Hsu, C. J., Yeh, M. L., & Renn, J. H. (2019). Intra-articular injection of platelet-rich plasma is superior to hyaluronic acid or saline solution in the treatment of mild to moderate knee osteoarthritis: a randomized, double-blind, triple-parallel, placebo-controlled clinical trial. Arthroscopy: The Journal of Arthroscopic & Related Surgery, 35(1), 106-117.
  8. Bannuru, R. R., Osani, M. C., Vaysbrot, E. E., Arden, N. K., Bennell, K., Bierma-Zeinstra, S. M. A., … & Blanco, F. J. (2019). OARSI guidelines for the non-surgical management of knee, hip, and polyarticular osteoarthritis. Osteoarthritis and cartilage.
  9. Jevsevar, D. S., Brown, G. A., Jones, D. L., Matzkin, E. G., Manner, P. A., Mooar, P., … & Goldberg, M. J. (2013). The American Academy of Orthopaedic Surgeons evidence-based guideline on: treatment of osteoarthritis of the knee. JBJS, 95(20), 1885-1886.
  10. Belzile, E. L., Deakon, R. T., Vannabouathong, C., Bhandari, M., Lamontagne, M., & McCormack, R. (2017). Cost-utility of a single-injection combined corticosteroid-hyaluronic acid formulation vs a 2-injection regimen of sequential corticosteroid and hyaluronic acid injections. Clinical Medicine Insights: Arthritis and Musculoskeletal Disorders, 10, 1179544117712993.
  11. Ayhan, E., Kesmezacar, H., & Akgun, I. (2014). Intraarticular injections (corticosteroid, hyaluronic acid, platelet rich plasma) for the knee osteoarthritis. World journal of orthopedics, 5(3), 351.
  12. McGibbon, C. & Mohamed, A. Knee Load Reduction From an Energy Storing Mechanical Brace. Canadian Society for Biomechanics (2018)
  13. Cook, C. S., & Smith, P. A. (2018). Clinical update: why PRP should be your first choice for injection therapy in treating osteoarthritis of the knee. Current reviews in musculoskeletal medicine, 11(4), 583-592.

By Simon Watts

Simon Watts is a former strength and conditioning coach with an extensive background in orthopedics and athletic therapy. He has a wealth of experience with the rehabilitation of common knee injuries such as osteoarthritis, meniscus tears, ligament injuries, and tendonitis. Simon studied Kinesiology at Dalhousie University, and as a track and field student-athlete was a national champion in the high jump and triple jump. He continues to be actively involved in the track and field community in Nova Scotia as a coach.

More posts by Simon Watts