Short answer
Some help a little, for a while. Steroid (corticosteroid) injections can ease knee osteoarthritis pain for a few weeks, but the benefit fades by around three to six months.2 Hyaluronic acid (“gel” or viscosupplement) injections give a reduction in pain too small for most people to notice, and platelet-rich plasma (PRP) did no better than salt-water placebo in a large trial.34 Injections are usually a short-term aid alongside exercise and weight management, not a substitute for them.1
Key points
- Steroid injections: moderate short-term pain relief; little or no effect by 3 to 6 months.
- Repeated steroid injections every 3 months for 2 years did not reduce pain and were linked to more cartilage loss.
- Hyaluronic acid: pain benefit below what patients notice, with more serious adverse events than placebo.
- PRP: no difference from placebo in pain or cartilage at 12 months in a large trial.
- Exercise remains one of the most important treatments.
The main types of knee injection
All of these are intra-articular injections, meaning they go directly into the knee joint. They differ in what is injected and in how good the evidence is.
| Injection | What it is | What the evidence shows | Evidence |
|---|---|---|---|
| Corticosteroid | An anti-inflammatory steroid | Pain relief for weeks; no clear effect at 6 months | Moderate |
| Hyaluronic acid | A gel-like substance similar to natural joint fluid | Pain reduction too small to matter; more serious adverse events than placebo | Strong |
| Platelet-rich plasma (PRP) | Concentrated platelets from your own blood | No better than placebo at 12 months in a large trial | Moderate |
Steroid injections
The NHS says steroid injections work quickly and can ease pain for several weeks or months, and are offered when other treatments have not worked.1 A 2015 Cochrane review of 27 trials with 1,767 people found a moderate benefit at 1 to 2 weeks, a smaller one at 4 to 6 weeks, a small and uncertain effect at 13 weeks and no evidence of effect at 26 weeks.2
In practical terms, at about one month 44% of people reported improvement after a steroid injection compared with 31% after a placebo injection.2 The reviewers rated the certainty as low because many trials were small and of variable quality. Side effects were reported at similar rates to placebo, but the authors said reliable safety data were lacking.2
Repeated injections raise a further question. In a trial of 140 people with knee osteoarthritis, steroid injections every 12 weeks for two years did not reduce pain compared with saline, and were associated with greater loss of cartilage thickness (about 0.21 mm compared with 0.10 mm).5 The authors concluded the findings did not support this treatment, although short-lived benefits between injections could have been missed.5
Hyaluronic acid (viscosupplementation)
Hyaluronic acid is a natural component of joint fluid, and injections were developed to “top up” lubrication. A 2022 BMJ systematic review included 169 trials with over 21,000 people.3 In the 24 largest placebo-controlled trials, the pain reduction was about 2 mm on a 100 mm scale, well below the threshold that patients would notice as meaningful.3
Serious adverse events were about 50% more common than with placebo (relative risk 1.49).3 The authors concluded that the findings do not support broad use of viscosupplementation for knee osteoarthritis.3
Platelet-rich plasma (PRP)
PRP is made by spinning a sample of your blood to concentrate the platelets, which carry growth factors, and injecting it into the knee. It is often promoted as able to repair cartilage. The RESTORE trial, published in JAMA in 2021, randomised 288 people aged 50 or over with knee osteoarthritis to three weekly injections of PRP or saline placebo.4
At 12 months there was no significant difference in pain, and no difference in cartilage volume measured on MRI scans. The authors stated that the findings do not support the use of PRP for knee osteoarthritis.4 Claims that PRP regrows cartilage are not supported by this trial.
Where injections fit in treatment
The NHS describes exercise as one of the most important treatments for osteoarthritis, whatever your age or fitness, along with losing weight if needed.1 Topical anti-inflammatory creams can be particularly effective for knee osteoarthritis, while paracetamol often does not work very well.1
The NHS positions steroid injections as an option when other treatments have not worked.1 For severe arthritis that does not respond, joint replacement or osteotomy (realigning the bone) may be discussed.1 Keyhole surgery is not an effective alternative; see does keyhole knee surgery help osteoarthritis.
Common questions
How long does a steroid injection last in the knee?
Usually a few weeks, sometimes longer. Trials show the clearest benefit in the first 6 weeks, with little evidence of effect at 3 to 6 months.2
Can injections regrow cartilage?
No injection has been shown to do this. PRP did not change cartilage volume compared with placebo, and repeated steroid injections were linked to more cartilage loss.45
Why do some people say gel or PRP injections worked for them?
Placebo injections themselves produce noticeable improvement. In the steroid review, 31% of people improved after placebo, and in RESTORE pain fell in both groups by similar amounts.24
Bottom line
A steroid injection can buy a few weeks of relief in knee osteoarthritis but does not change the course of the disease, and frequent repeat injections are questionable. Hyaluronic acid and PRP injections have not shown meaningful benefit in the best trials. Exercise and weight management remain the foundation.
Related reading
- Orthopaedics overview
- Does Keyhole Knee Surgery Help Osteoarthritis?
- Partial vs Total Knee Replacement: What Is the Difference?
- Does Exercise Before Joint Replacement Help?
Sources
- NHS. Osteoarthritis: treatment. NHS website. https://www.nhs.uk/conditions/osteoarthritis/treatment/ Accessed 5 November 2026.
- Jüni P, Hari R, Rutjes AWS, Fischer R, Silletta MG, Reichenbach S, da Costa BR. Intra-articular corticosteroid for knee osteoarthritis. Cochrane Database of Systematic Reviews; 2015;(10):CD005328. https://www.cochrane.org/CD005328/MUSKEL_intra-articular-corticosteroid-knee-osteoarthritis Accessed 5 November 2026.
- Pereira TV, Jüni P, Saadat P, et al. Viscosupplementation for knee osteoarthritis: systematic review and meta-analysis. BMJ; 2022;378:e069722. https://doi.org/10.1136/bmj-2022-069722
- Bennell KL, Paterson KL, Metcalf BR, et al. 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; 2021;326(20):2021–2030. https://doi.org/10.1001/jama.2021.19415
- McAlindon TE, et al. Randomised trial of intra-articular triamcinolone vs saline every 12 weeks for two years in knee osteoarthritis. JAMA; 2017. https://doi.org/10.1001/jama.2017.5283 (summary via EurekAlert news release: https://www.eurekalert.org/news-releases/498783 Accessed 5 November 2026.)
Article history
- — First published.