A gel injection can ease knee arthritis pain for some people, but in the largest and most careful trials the average benefit over a salt-water injection is small.[1, 2] This article explains what a hyaluronic acid injection is, how well it works, how it compares with cortisone, what the risks are and where it fits alongside other treatments for osteoarthritis of the knee.
At a glance
- Hyaluronic acid injections aim to ease pain and stiffness, but they do not regrow cartilage.
- The average benefit over a salt-water injection is small, and reviews and guidelines disagree on how useful it is.
- Cortisone works faster, while hyaluronic acid builds up over weeks and may last a little longer.
- Exercise, weight management and education remain the foundation of treatment, with or without an injection.
What is a hyaluronic acid injection and what is it meant to do?
Hyaluronic acid is a natural part of the fluid inside your knee. It helps the joint glide smoothly and absorbs some of the load when you walk. In osteoarthritis, the fluid becomes thinner and holds less hyaluronic acid.
A hyaluronic acid injection, also called a gel injection or viscosupplementation, places a manufactured form of this substance into the joint. The aim is to ease pain and stiffness. Some products are given as a single injection and others as a course of injections a week apart. They also differ in how thick the gel is and how it is made. Durolane, Euflexxa and Synvisc are common brands.[3]
The injection does not regrow worn cartilage or reverse arthritis. Over three years, X-ray signs of arthritis kept progressing in people who had hyaluronic acid injections, as they did in people who had cortisone.[4]
How well do hyaluronic acid injections work?
This is where the evidence is divided. On average, hyaluronic acid lowers pain by only about 2 points on a 100-point scale more than a salt-water injection. That is smaller than the change most people would notice.[1]
Not every expert reads the evidence the same way. Most published reviews, including the better-quality ones, report a statistically significant improvement in pain and function.[5] The benefit tends to look larger in small studies than in the largest ones, which is one reason the conclusions differ.[1]
Part of the relief people feel after any knee injection comes from the injection itself. A salt-water injection lowers pain by about 13 points on a 100-point scale for up to six months, and about half of people improve enough to count as a meaningful response.[6] So if you feel better after a gel injection, some of that improvement would probably have happened anyway.
When hyaluronic acid does help, the effect usually appears by about four weeks, is greatest at around eight weeks and fades over six months.[7]
How does it compare with a cortisone injection?
The two injections work on different timelines. Cortisone, a strong anti-inflammatory medicine, eases pain faster. It gives better relief at two weeks, the two are similar at four weeks, and hyaluronic acid does slightly better at three and six months.[8]
The most reliable evidence leans towards cortisone in the short term. A cortisone injection is the most likely of all knee injections to give a worthwhile benefit at two to six weeks, while hyaluronic acid shows no clear effect on pain compared with placebo.[2] When the two are compared directly, results are similar, with a small longer-term pain advantage for hyaluronic acid that falls short of a difference most people would notice.[9]
In practice, cortisone is often used to settle a painful flare quickly, and hyaluronic acid is sometimes chosen when a slower, longer-lasting effect is the goal.[10] If you are also weighing up platelet-rich plasma, the article on whether PRP injections work for knee osteoarthritis compares it with hyaluronic acid.
Who might consider a hyaluronic acid injection?
For everyone with knee osteoarthritis, the core treatments are education about the condition, a structured exercise programme and, where it applies, weight management.[11] Injections are an add-on for people whose pain persists despite these and simpler medicines. They are not a substitute for strengthening work. You can read more about these first steps in the guide to non-surgical options for knee osteoarthritis.
Guidelines disagree about hyaluronic acid. Some, including the American Academy of Orthopaedic Surgeons and the National Institute for Health and Care Excellence in the United Kingdom, advise against routine use. Others give it conditional support for selected people.[12] Where it is supported, it is suggested for people whose pain persists despite first-line treatment, including those who cannot take anti-inflammatory tablets.[11, 13] Reported benefits are greatest in mild to moderate arthritis.[12]
Hyaluronic acid is generally not injected into a hot, swollen knee during a flare. That situation needs to be assessed first.[14]
What are the risks?
Most side effects are mild and settle within a few days. About 1 in 7 people have short-lived pain, swelling or warmth in the knee after the injection, only slightly more often than after a salt-water injection.[15]
Less often, the knee becomes hot, swollen and very painful within a day or two. This is an inflammatory reaction to the gel, sometimes called a pseudoseptic reaction because it can look like infection. It happens after about 1 in 100 injections or fewer, although rates of a few in 100 have been reported.[16] Because it can be hard to tell apart from infection, a knee that becomes hot and swollen after an injection should be checked promptly.
Infection is rare, reported in about 1 in 1,000 people treated with hyaluronic acid.[17] Serious adverse events are slightly more common than after a salt-water injection, although it is not clear how many are caused by the injection itself.[1, 2]
Can it delay a knee replacement?
People who have hyaluronic acid injections tend to have a knee replacement later, by about 10 months on average.[18] This does not prove that the injection caused the delay, because people who choose injections may differ in other ways, such as their general health or how severe their arthritis is.[18]
The time from a first injection to total knee replacement is also similar after hyaluronic acid and after cortisone, at about 12 months.[19] If your pain and function already make surgery the right choice and you are ready for it, an injection given only to put off the operation is not recommended.[20] The article on when to have a knee replacement covers that decision in more detail.
Summary
It is reasonable to discuss a hyaluronic acid injection if your knee arthritis pain persists despite exercise, weight management and simple medicines, provided you expect a modest and temporary benefit and understand that the evidence is divided.
If you would like to discuss how this applies to your knee, you can book a consultation with Dr Vishal Pai.
References
Show all 20 referencesHide references
- Pereira TV et al. 2022. Viscosupplementation for knee osteoarthritis: systematic review and meta-analysis. BMJ.
- Pereira TV et al. 2024. Effectiveness and safety of intra-articular interventions for knee and hip osteoarthritis based on large randomized trials: a systematic review and network meta-analysis. Osteoarthritis and Cartilage.
- Peck J et al. 2021. A comprehensive review of viscosupplementation in osteoarthritis of the knee. Orthopedic Reviews.
- Bensa A et al. 2025. Effect of corticosteroids and hyaluronic acid injections on knee osteoarthritis trajectory. Journal of Experimental Orthopaedics.
- Bruyère O et al. 2025. Effects of intra-articular hyaluronic acid injections on pain and function in patients with knee osteoarthritis: an umbrella review of systematic reviews and meta-analyses of randomized placebo-controlled trials. Maturitas.
- Previtali D et al. 2020. The long-lasting effects of “placebo injections” in knee osteoarthritis: a meta-analysis. Cartilage.
- Bannuru RR et al. 2011. Therapeutic trajectory following intra-articular hyaluronic acid injection in knee osteoarthritis: meta-analysis. Osteoarthritis and Cartilage.
- Bannuru RR et al. 2009. Therapeutic trajectory of hyaluronic acid versus corticosteroids in the treatment of knee osteoarthritis: a systematic review and meta-analysis. Arthritis Care and Research.
- Bensa A et al. 2024. Corticosteroid injections for knee osteoarthritis offer clinical benefits similar to hyaluronic acid and lower than platelet-rich plasma: a systematic review and meta-analysis. EFORT Open Reviews.
- Pesare E et al. 2023. Italian Orthopaedic and Traumatology Society (SIOT) position statement on the non-surgical management of knee osteoarthritis. Journal of Orthopaedics and Traumatology.
- Bannuru RR et al. 2019. OARSI guidelines for the non-surgical management of knee, hip, and polyarticular osteoarthritis. Osteoarthritis and Cartilage.
- Glinkowski W et al. 2025. Intra-articular hyaluronic acid for knee osteoarthritis: a systematic umbrella review. Journal of Clinical Medicine.
- Arden NK et al. 2020. Non-surgical management of knee osteoarthritis: comparison of ESCEO and OARSI 2019 guidelines. Nature Reviews Rheumatology.
- Conrozier T et al. 2024. EUROVISCO consensus guidelines for the use of hyaluronic acid viscosupplementation in knee osteoarthritis based on patient characteristics. Cartilage.
- Miller LE et al. 2019. Safety of intra-articular hyaluronic acid for knee osteoarthritis: systematic review and meta-analysis of randomized trials involving more than 8,000 patients. Cartilage.
- Sherman SL et al. 2025. Severe acute localized reaction/pseudosepsis in patients with knee osteoarthritis receiving injections of hyaluronic acid: a targeted literature review. Orthopedics. Funded by Sanofi.
- Bensa A et al. 2025. Safety profile comparison of intra-articular corticosteroids, hyaluronic acid, platelet-rich plasma, and cell-based injections for knee osteoarthritis: a systematic review and meta-analysis by the ESSKA Orthobiologics Initiative. Knee Surgery, Sports Traumatology, Arthroscopy.
- Berkani S et al. 2022. Time to total knee arthroplasty after intra-articular hyaluronic acid or platelet-rich plasma injections: a systematic literature review and meta-analysis. Journal of Clinical Medicine.
- Gesheff MG et al. 2024. Time to total knee arthroplasty (TKA) post intra-articular injection. Journal of Clinical Medicine.
- Tang A et al. 2021. Do preoperative intra-articular corticosteroid and hyaluronic acid injections affect time to total joint arthroplasty? Journal of Clinical Orthopaedics and Trauma.
Frequently Asked Questions
How soon will I notice a difference, and how long does it last?
Any benefit usually builds over the first four weeks and is greatest at around eight weeks.[7] It then fades gradually, with a small effect still detectable at six months. Not everyone notices a change.
Will it stop my arthritis getting worse?
There is no good evidence that hyaluronic acid slows or reverses arthritis. Over three years, X-ray changes progressed after hyaluronic acid injections, as they did after cortisone.[4] The injection is a way to manage symptoms, not to repair the joint.
Can I have one if I am planning a knee replacement?
Injections are usually avoided in the three months before joint replacement surgery. Injections given at least three months beforehand do not appear to increase complications after surgery.[20] If you have had an injection recently, tell your surgeon when you discuss the timing of your operation.
Wondering whether an injection suits your knee?
Dr Vishal Pai assesses and treats knee arthritis, from non-surgical care through to knee replacement. You can arrange a consultation to talk through the options that may suit your circumstances.
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.