Which Knee Injection Is Best for Osteoarthritis? Steroid, Hyaluronic Acid, PRP and Hydrogel Compared

Written by the LSRI clinical team and medically reviewed by Dr Prashant Sankaye, Consultant MSK Radiologist, on 2 October 2026.

“Which knee injection is best for my arthritis?” is one of the questions we are asked most often. The honest answer is that there is no single best injection for everyone. Each option works differently, the quality of evidence varies a great deal, and the right choice depends on your symptoms, your scan findings and what you want to achieve. This guide compares the four main options: steroid, hyaluronic acid, platelet-rich plasma (PRP) and polyacrylamide hydrogel. You can read more about the condition in our knee osteoarthritis guide and about the procedures on our knee injections page.

Start with the foundations: exercise and weight

Before comparing injections, it is worth being clear about what the evidence supports most strongly. Therapeutic exercise tailored to each person, such as local muscle strengthening and general aerobic fitness, is recommended for everyone with osteoarthritis. For people living with overweight or obesity, weight loss improves quality of life and physical function and reduces pain, and any amount of weight loss is likely to help, with 10% of body weight likely to be better than 5%.

Injections are best seen as a way to support these foundations, for example by easing pain enough to make exercise possible, rather than as a replacement for them.

Steroid (corticosteroid) injections

A steroid injection delivers a strong anti-inflammatory medicine directly into the knee joint. It is most useful when the knee is flaring, swollen or inflamed.

A steroid injection is usually considered when other pain medicines are ineffective or unsuitable, or to support therapeutic exercise. It gives short-term relief, typically for 2 to 10 weeks. A 2015 Cochrane review found that effects tend to decrease over time, and found no evidence of an effect remaining six months after the injection. The reviewers also noted that whether there are clinically important benefits in the first one to six weeks remains unclear because of the quality of the trials.

NHS patient information from Guy’s and St Thomas’ notes that relief typically begins after 1 to 2 days³. In practice, a steroid injection can give a useful window of relief to get moving and start a rehabilitation programme. Steroid can temporarily raise blood glucose, so people with diabetes will be advised to monitor their levels closely afterwards³.

Hyaluronic acid injections

Hyaluronic acid is a natural component of joint fluid that helps lubricate and cushion the joint. Hyaluronic acid injections (sometimes called viscosupplementation) aim to supplement this.

A 2022 systematic review and meta-analysis in the BMJ, which pooled large placebo-controlled trials, concluded that hyaluronic acid leads to a small reduction in knee pain compared with placebo, but less than the difference considered clinically important. The same review found an increased risk of serious adverse events compared with placebo, and concluded that the findings do not support broad use⁵.

We offer hyaluronic acid injections at LSRI, for osteoarthritis and for some sports injuries. They may be an option, for example, if steroid is unsuitable for you or has not helped. Dr Sankaye will explain the evidence so that you can make an informed decision.

Platelet-rich plasma (PRP)

PRP is made from a sample of your own blood, which is spun in a centrifuge to concentrate the platelets. Platelets contain growth factors, and the idea is that injecting them into the knee may influence inflammation and pain.

The evidence is mixed. The 2021 RESTORE trial in JAMA compared PRP with a saline placebo in people with mild to moderate knee osteoarthritis and found no significant difference in pain or cartilage volume at 12 months⁶. On the other hand, a 2025 meta-analysis of 11 placebo-controlled trials in Joint Bone Spine found a weak benefit on pain at three and six months, but not at 12 months, and concluded that the clinical relevance of PRP is debatable⁷. One difficulty is that PRP preparations differ between studies, which makes results hard to compare.

If PRP is being considered, it is usually for people with milder osteoarthritis who understand the uncertainty.

Polyacrylamide hydrogel

Polyacrylamide hydrogel is a newer type of injection. It is given as a single injection and is designed to be longer-acting than hyaluronic acid.

The evidence is growing but still limited. A 2024 randomised trial in Clinical and Experimental Rheumatology of 239 adults with moderate to severe knee osteoarthritis found that a single hydrogel injection was non-inferior (not meaningfully worse) than hyaluronic acid for pain at one year⁹. A 3-year follow-up of people from the hydrogel group reported sustained improvement in pain, and no adverse events between years one and three were assessed as related to the injection¹⁰. However, the follow-up was open-label with no comparison group, a number of participants did not complete it, and some of the researchers have received funding from the manufacturer. Longer, independent comparisons against placebo are still needed.

At a glance: comparison table

This table summarises the options in general terms. Individual responses vary.

Why ultrasound guidance and aspiration matter

At LSRI, knee injections are given under ultrasound guidance by a consultant musculoskeletal radiologist. The scan comes first. It shows whether there is fluid in the joint, whether there is thickening of the joint lining, and whether another problem, such as a Baker’s cyst or a tendon or bursa problem, could be contributing to your pain. This helps decide whether an injection is appropriate and which one.

If there is a significant effusion (fluid on the knee), it can often be drained (aspirated) through the same needle before the injection. This can relieve pressure and allows the fluid to be sent for testing if there is any concern about infection or crystal arthritis such as gout. Watching the needle on screen also lets the clinician confirm that the medicine is placed in the joint rather than the surrounding tissue.

Frequently asked questions

Which knee injection lasts the longest?

Polyacrylamide hydrogel has been followed for the longest period in studies, but that evidence is limited. Steroid has the shortest expected duration. How long any injection helps varies from person to person.

Will an injection repair my cartilage?

No injection has been shown to regrow cartilage. The aim is to reduce pain and improve function so that you can stay active.

Can I have more than one type of injection?

Sometimes. For example, a steroid injection might be used to settle a flare, with other options discussed later. Dr Sankaye will consider your history and scan findings before advising.

Is an injection an alternative to knee replacement?

For some people, injections help manage symptoms for a period. They do not prevent osteoarthritis from progressing, and for severe osteoarthritis, a referral to discuss surgery may be more appropriate.

Do I need a scan first?

At LSRI, every injection begins with an ultrasound scan of the knee. If you already have an X-ray or MRI, please bring the report.

Book an appointment

Call 0203 633 5040 or book online. Clinics at Harley Street (W1G 9QJ) and Harrow (HA2 7SJ).

References

1. Bannuru RR, Osani MC, Vaysbrot EE, et al. OARSI guidelines for the non-surgical management of knee, hip, and polyarticular osteoarthritis. Osteoarthritis Cartilage 2019;27(11):1578-1589. doi:10.1016/j.joca.2019.06.011
2. Kolasinski SL, Neogi T, Hochberg MC, et al. 2019 American College of Rheumatology/Arthritis Foundation guideline for the management of osteoarthritis of the hand, hip, and knee. Arthritis Care Res (Hoboken) 2020;72(2):149-162. doi:10.1002/acr.24131
3. Guy’s and St Thomas’ NHS Foundation Trust. Steroid injections for joint and tendon pain (patient information, last reviewed February 2026). https://www.guysandstthomas.nhs.uk/health-information/steroid-injections-joint-and-tendon-pain
4. Jüni P, Hari R, Rutjes AW, et al. Intra-articular corticosteroid for knee osteoarthritis. Cochrane Database Syst Rev 2015;CD005328. doi:10.1002/14651858.CD005328.pub3
5. Pereira TV, Jüni P, Saadat P, et al. Viscosupplementation for knee osteoarthritis: systematic review and meta-analysis. BMJ 2022;378:e069722. doi:10.1136/bmj-2022-069722
6. 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. doi:10.1001/jama.2021.19415
7. Auroux M, Debionne T, Mainbourg S, Chapurlat R. Efficacy of intra-articular platelet-rich plasma compared with placebo in knee osteoarthritis: a systematic review and meta-analysis. Joint Bone Spine 2025;92(6):105947. doi:10.1016/j.jbspin.2025.105947
8. American College of Rheumatology. 2026 update of the ACR recommendations for the management of osteoarthritis of the knee, hip, and hand: summary of recommendations (approved 8 September 2026). https://assets.contentstack.io/v3/assets/bltee37abb6b278ab2c/bltb3d12c34020da842/oa-guideline-summary-2026.pdf
9. Bliddal H, Beier J, Hartkopp A, Conaghan PG, Henriksen M. Polyacrylamide gel versus hyaluronic acid for the treatment of knee osteoarthritis: a randomised controlled study. Clin Exp Rheumatol 2024;42(9):1729-1735. doi:10.55563/clinexprheumatol/i3fqee
10. Bliddal H, Beier J, Hartkopp A, Conaghan PG, Henriksen M. Three-year follow-up from a randomised controlled trial of a single intra-articular polyacrylamide hydrogel injection in subjects with knee osteoarthritis. Clin Exp Rheumatol 2026;44(5):996-1003 (online 2025). doi:10.55563/clinexprheumatol/5lofry