Do injections improve knee pain?
Joint injections are often suggested or prescribed as conservative treatment for people with knee pain especially when its due to osteoarthritis. GP, surgeons and physiotherapists all often look to injection therapy as a valid method of treatment for knee pain. In this article I will touch on three of the major options for injections and what the evidence is to support their use.
Types of Injections
Corticosteroids are the oldest of the injections covered in this article, having been around since the 1950’s, and are well accepted within western society and its medical model. Also known as ‘Cortisone’, corticosteroids are essentially synthetic versions of the natural human hormone cortisol. Cortisone is an anti-inflammatory drug which is injected into joints, muscles, around nerves and into the blood in an attempt to reduce inflammation. This drug is often injected in conjunction with a local anaesthetic agent for further pain relief (2).
Hyaluronic Acid (HA)
In a synovial joint (most joints within the body), there is synovial fluid which maintains joint health and ease of movement. Hyaluronic acid is viscoelastic glycosaminoglycan that is naturally present in healthy synovial joint fluid and this is a relatively new type of injection. Injections come under the brand names of Synvisc & Osteoartz. The aim of these products is to provide protective properties to the joint fluid including shock absorption, traumatic energy dissipation, protective coating of the articular cartilage surface, and lubrication. The rationale, biologically, is that the viscosity of the joint fluid is increased and this will improve joint health (2).
PRP is an injection made from an autologous blood sample which is rich in, you guessed it, platelets. Blood is removed from the same person receiving the injection, spun in a centrifuge to separate the bloods components and then the PRP component is reinjected into the target site within the body. The plasma which is filled with platelets is high in growth factors and aids the body’s natural healing process. The science behind PRP has been around since the 1970’s however it has become more popularised in recent years for use in sporting injuries and musculoskeletal conditions (10).
Image: the process of separation of blood components for PRP injections
Do they work?
A 2009 systematic review of level 1 evidence found that corticosteroids were effective in pain reduction for 1-week post injection in knee OA patients. However, when compared to a placebo, there was no consistent evidence of better pain relief over longer periods (Hepper 2009). A 2004 study also found corticosteroids effective for 2-weeks but this study was also able to show some evidence of reduced pain at 16-24 weeks (11).
Several studies have shown that PRP injections are more efficacious for knee OA pain relief than placebo injections (1, 7). I will dive into PRP’s promising results in the next section.
It is worth noting The Royal Australian College of General Practitioners current recommendations for intra-articular injections of knee and hip osteoarthritis. At the time of writing in September 2020, they are as follows:
- Corticosteroid = recommended
- PRP = neutral recommendation
- Viscosupplementation (Hyaluronic Acid) = recommendation against (9)
This is helpful to know as this is what may inform your GP’s opinion on each of the discussed injections. Find the up to date guidelines HERE>>.
Which one is best?
The answer to this question is multifaceted and individualised. Treatments that are effective for some may not be effective for others. Further to this, there are factors such as ease of availability and the cost of each injection. PRP injections can cost hundreds of dollars per injection whereas corticosteroids may cost the patient nothing if it is bulk-billed.
In terms of scientific evidence, several meta-analyses have been published comparing PRP to other injection options. In 2020, a meta-analysis of 34 randomised control trials (RCT’s) looking at knee osteoarthritis found that PRP was (5):
- PRP was better than placebo overall at 12 months follow-up. PRP had reduced pain at 6-months and reduced stiffness at 3 and 6 months compared to placebo injections.
- PRP was better than hyaluronic acid at overall 6 and 12 month follow ups. Pain was better at 6 months and 12 months, stiffness was better at 3, 6 and 12 months.
- PRP was favourable over steroids in this study however this was based on limited data.
- There no real evidence that PRP was any better in short term (1-3months)
The superior effects of PRP for knee OA are replicated in the literature through multiple other meta-analyses and systematic review studies (3,4,6,8).
PRP injections are also being studied for use in augmenting healing for many other knee injuries. In 2020 a systematic review and meta-analysis study was published on the use of PRP for different knee pathologies, a summary of its results are as follows (12):
- Patella Tendinitis: a non-significant difference in favour of PRP over saline injection, dry needling, shockwave therapy.
- Muscle Injury: a small significant difference in return to sport time in favour of using PRP with a physiotherapy rehab program however the cost-effectiveness of this was questioned due to only a small improvement.
- ACL Reconstruction: no significant difference with the use of PRP.
- Meniscal Repair: there was a significant difference in favour of PRP for improving repair failure rates but no significant difference for improving function.
Take Home Points
- There is evidence in the scientific literature that corticosteroids, hyaluronic acid, and platelet rich plasma injections can be effective for reducing knee pain.
- The scientific evidence is limited by poor quality evidence and differences between study methods.
- Corticosteroids likely have a short-term effect on pain when used for chronic conditions such as knee osteoarthritis.
- PRP appears to be the most effective type of injection for long-term pain and stiffness relief.
- Injections can be a helpful adjunct treatment option but should not be stand-alone treatment. Exercise and weight loss are still the gold-standard treatments for knee osteoarthritis.
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- Laudy ABM, Bakker EWP, Rekers M, et al Efficacy of platelet-rich plasma injections in osteoarthritis of the knee: a systematic review and meta-analysis British Journal of Sports Medicine 2015;49:657-672.
- Bannuru, R. R., Natov, N. S., Obadan, I. E., Price, L. L., Schmid, C. H., & McAlindon, T. E. (2009). Therapeutic trajectory of hyaluronic acid versus corticosteroids in the treatment of knee osteoarthritis: A systematic review and meta-analysis. Arthritis & Rheumatism, 61(12), 1704-1711.
- Campbell, K. A., Erickson, B. J., Saltzman, B. M., Mascarenhas, R., Bach, B. R., Cole, B. J., & Verma, N. N. (2015). Does Intra-articular Platelet-Rich Plasma Injection Provide Clinically Superior Outcomes Compared With Other Therapies in the Treatment of Knee Osteoarthritis? A Systematic Review of Overlapping Meta-analyses. Arthroscopy: The Journal of Arthroscopic & Related Surgery, 31(11).
- Dai, W., Zhou, A., Zhang, H., & Zhang, J. (2017). Efficacy of platelet-rich plasma in the treatment of knee osteoarthritis: A meta-analysis of randomized controlled trials. Arthroscopy: The Journal of Arthroscopic & Related Surgery, 33(3), 659-670.e1.
- Filardo, G., Previtali, D., Napoli, F., Candrian, C., Zaffagnini, S., & Grassi, C. (2020). PRP Injections for the Treatment of Knee Osteoarthritis: A Meta-Analysis of Randomized Controlled Trials. Cartilage.
- Han, Y., Huang, H., Pan, J., Lin, J., & Zeng, L. (2019). Meta-analysis Comparing Platelet-Rich Plasma vs Hyaluronic Acid Injection in Patients with Knee Osteoarthritis. Pain Medicine, 20(7).
- Meheux, C. J., McCulloch, P. C., Lintner, D. M., Varner, K. E., & Harris, J. D. (2016). Efficacy of intra-articular platelet-rich plasma injections in knee osteoarthritis: A systematic review. Arthroscopy: The Journal of Arthroscopic & Related Surgery, 32(3), 495-505.
- Moen, M., Weir, A., Bakker, E., Rekers, M., & Laudy, G. (2016). Efficacy of platelet-rich plasma injections in osteoarthritis of the knee: An updated systematic review and meta-analysis. Osteoarthritis and Cartilage, 24, S520-S521.
- The Royal Australian College of General Practitioners. (n.d.). Intra-articular injections. RACGP – The Royal Australian College of General Practitioners. Retrieved September 17, 2020, from https://www.racgp.org.au/clinical-resources/clinical-guidelines/key-racgp-guidelines/view-all-racgp-guidelines/knee-and-hip-osteoarthritis/recommendations/pharmacological-interventions/intra-articular-injections
- Wasterlain, A. S., Braun, H. J., Dragoo, J. L., Harris, A., & Kim, H. J. (2012). The systemic effects of platelet-rich plasma. American Journal of Sports Medicine.
- Arroll Bruce, Goodyear-Smith Felicity. Corticosteroid injections for osteoarthritis of the knee: meta-analysis BMJ 2004; 328 :869
- Trams, E., Kulinski, K., Kozar-Kaminska, K., Pomianowski, S., & Kaminski, R. (2020). The clinical use of platelet-rich plasma in knee disorders and surgery—A systematic review and meta-analysis. Life, 10(6), 94