Knee Arthritis Injections: PRP, Steroid, Hyaluronic Acid and Arthrosamid Explained
Clinical Summary from Dr David Samra
Dr David Samra is a Fellowship-trained Sport and Exercise Medicine Physician with clinical experience treating knee osteoarthritis and bone stress injuries in both athletes and the general population.
Several injections are used to manage symptomatic knee osteoarthritis, including corticosteroid, platelet-rich plasma (PRP), hyaluronic acid and more recently polyacrylamide hydrogel injections such as Arthrosamid. The evidence supporting these treatments varies.
Corticosteroid injections are supported for short-term pain relief, while evidence for PRP and hyaluronic acid remains mixed across studies. Arthrosamid is a newer treatment designed to remain permanently within the joint, and early studies suggest it may provide longer-lasting symptom improvement in some patients. Any permanent implant in a joint needs to be carefully considered. However, cost is very high, long-term evidence remains limited and further independent research is required.
Dr Samra discusses these options with patients as part of a broader management strategy for knee osteoarthritis that prioritises exercise therapy, load management and rehabilitation.
Last reviewed:
March 2026
Author Dr David Samra, MBBS (Hons), MD, FACSEP – Sport and Exercise Medicine Physician
Knee osteoarthritis is one of the most common reasons people develop ongoing knee pain, particularly as they move into their 40s, 50s and beyond. It is the most common reason for presentation to our Sports Medicine clinic. Many patients want to remain active and avoid or delay knee replacement surgery, which is why non-surgical treatments such as joint injections are frequently discussed. These injectable treatments are often considered when physiotherapy, exercise and lifestyle strategies are not providing enough functional benefit to patients.
Several types of injections are available for knee osteoarthritis. These include:
- corticosteroid injections
- hyaluronic acid injections
- platelet-rich plasma (PRP)
- polyacrylamide hydrogel injections such as Arthrosamid
Each injection works differently and the scientific evidence supporting them varies.
This article explains the research evidence, benefits, limitations and safety considerations of the most commonly used knee arthritis injections.
What causes Knee Osteoarthritis?
Knee osteoarthritis develops when the structures within the joint gradually deteriorate over time. The process typically involves thinning of the articular cartilage, changes in the underlying bone, inflammation of the synovial lining, and degeneration of the meniscus. These structural changes alter how forces are transmitted across the joint and can lead to symptoms such as knee pain, swelling, stiffness and reduced mobility.
Although osteoarthritis cannot currently be reversed, symptoms can often be managed effectively for many years with the right combination of exercise therapy, load management, rehabilitation and, when appropriate, injection treatments.
When are Knee Joint Injections Considered?
Most modern treatment guidelines recommend starting with non-surgical treatments.
These typically include:
- exercise therapy
- strength training
- weight management
- activity modification
- physiotherapy
- appropriate pain medication.
If symptoms persist despite these measures, injections may be considered.
Injections are primarily used to reduce pain, improve mobility, facilitate rehabilitation and delay surgery.
Types of injections for knee osteoarthritis
There are four commonly discussed injection options.
- Corticosteroid injections
- Hyaluronic acid injections
- Platelet-rich plasma (PRP)
- Arthrosamid (polyacrylamide hydrogel)
Each has different evidence, duration of benefit and cost.
Corticosteroid (cortisone) Injections for Knee Osteoarthritis
Corticosteroid injections have been used for decades to treat painful joints.
They work primarily by reducing inflammation inside the joint.
Effectiveness
Clinical guidelines suggest corticosteroid injections can provide short-term symptom relief, usually lasting several weeks to a few months.
Most guidelines (AAOS and others), show consensus that corticosteroid injections may provide short-term relief in knee osteoarthritis.
Advantages
- widely available
- inexpensive
- rapid onset of pain relief
Limitations
Repeated steroid injections may have negative effects on joint cartilage in some circumstances.
One study of multiple cortisone injections (4 per calendar year over 2 years!) demonstrated faster cartilage wear (McAlindon et al 2017)
A more recent study by Latourte et al in 2022 demonstrated that patients who had corticosteroid injections were no more likely to experience clinical or x-ray over 5 years.
Because of this, they are usually used sparingly rather than repeatedly over many years.
Hyaluronic Acid Injections for Knee Osteoarthritis
Hyaluronic acid (HA) injections are sometimes described as “joint lubrication injections.”
Hyaluronic acid is a normal component of joint fluid.
Effectiveness
Evidence for HA injections has been mixed.
Some patients report improvement in symptoms, but large guideline reviews have found the average benefit across studies is modest.
The Australian OA Knee Clinical Care Standard does not recommend routine use of hyaluronic acid injections for knee osteoarthritis.
Australian Commission for Safety and Quality in Healthcare
Advantages
- generally safe
- resorbable (the body eventually absorbs it, i.e not a permanent implant)
Limitations
- variable effectiveness and duration of benefit
- effect size of benefit may be modest.
Platelet-Rich Plasma (PRP) injections
PRP injections use a patient’s own blood.
Blood is processed to concentrate platelets, which contain growth factors involved in tissue healing.
The platelet-rich plasma is then injected into the joint.
Effectiveness
Many studies suggest PRP may improve pain and function in knee osteoarthritis.
However, results vary significantly because PRP preparation methods differ widely between clinics.
The AAOS guideline states PRP may reduce pain and improve function, but evidence quality remains limited.
A recent high quality RCT (the most believable form of clinical research) demonstrated no benefit to PRP injections over placebo for medial knee OA.
Bennell et al 2021
Advantages
- uses the patient’s own blood (autologous and safe)
- non-permanent
- may have longer effects than steroid injections
Limitations
- preparation methods vary (there is no established 'gold-standard')
- evidence quality varies between studies, and the higher the quality the lower the effect size of PRP
- usually requires multiple injections.
Arthrosamid injections for Knee Osteoarthritis
Arthrosamid is a newer injection that has received increasing attention internationally.
Unlike most other injections, Arthrosamid is not biodegradable.
It is a polyacrylamide hydrogel implant injected into the knee joint.
What is Arthrosamid made of?
Arthrosamid contains:
- 2.5% polyacrylamide hydrogel
- 97.5% water
Once injected into the knee joint, the hydrogel integrates with the synovial membrane, which lines the joint.
Unlike steroid, PRP or hyaluronic acid injections, the material is considered an "implant" and is designed to
remain permanently in the joint.
How does Arthrosamid work?
The proposed mechanism includes:
- integration into the synovial lining
- improved joint lubrication
- reduced friction between joint surfaces
- improved mechanical environment within the knee.
Preclinical research suggests the hydrogel becomes incorporated into synovial tissue rather than remaining freely floating.
Christensen L et al. Osteoarthritis Cartilage
Clinical research on Arthrosamid - Beware of Sources of Bias
Early studies
Initial observational studies reported improvements in pain and function following injection.
Henriksen et al. demonstrated improvements in WOMAC pain scores that persisted at 13 months.
Henriksen M et al. Clin Exp Rheumatol
https://pubmed.ncbi.nlm.nih.gov/30148430/
Because this study was NOT placebo controlled and there may be commercial conflicts of interest, the results should be interpreted cautiously.
Randomised controlled trial
A later randomised double-blind trial compared Arthrosamid with hyaluronic acid injections.
The study found:
- Arthrosamid was non-inferior to hyaluronic acid
- both groups improved significantly
- improvements were maintained at 12 months
Bliddal H et al. Clin Exp Rheumatol
https://pubmed.ncbi.nlm.nih.gov/38525999/
Long-term follow-up studies
Follow-up studies suggest improvements may last several years.
3-year outcomes
Patients continued to demonstrate improved WOMAC pain scores at three years.
Bliddal H et al. https://doi.org/10.55563/clinexprheumatol/5lofry
5-year outcomes
Five-year data also showed sustained improvements in symptoms.
Bliddal H et al. https://doi.org/10.55563/clinexprheumatol/bsper8
These studies indirectly suggest Arthrosamid may provide longer lasting symptom relief than many other injections (no direct comparison)
However, these longer-term studies were "extension studies" without control groups.
Does Arthrosamid cure Osteoarthritis?
No.
Current research suggests Arthrosamid is symptom-modifying rather than disease-modifying.
It improves pain and function but there is no convincing evidence yet that it reverses osteoarthritis or prevents knee replacement surgery.
Is Arthrosamid really a lifetime injection?
The hydrogel itself is designed to remain permanently in the joint.
However, clinical evidence currently demonstrates improvement for up to five years, not a lifetime.
Therefore it is more accurate to describe Arthrosamid as a long-acting implant, rather than a proven lifetime cure.
Safety of Arthrosamid Injections
Clinical studies suggest short- and medium-term safety is generally reassuring.
In the randomised trial comparing Arthrosamid with hyaluronic acid:
- adverse events were more frequent with Arthrosamid
- most were mild or moderate
- no serious device-related complications were reported.
Bliddal H et al.
https://pubmed.ncbi.nlm.nih.gov/38525999/
Common side effects include:
- temporary swelling
- pain after injection
- Baker’s cyst swelling.
Infection risk appears low but exists with any joint injection.
Could Permanent Implants Cause Problems Later? Are Foreign Body Reactions Possible?
The permanent nature of Arthrosamid is both its main advantage and its main uncertainty.
Because the material is not absorbed by the body:
- rare inflammatory reactions could persist
- removal may be difficult
- long-term biological effects remain under investigation.
For this reason careful patient selection and counselling are important.
Histological research suggests polyacrylamide hydrogel integrates into synovial tissue.
Christensen LH and Daugaard S
However, rare inflammatory reactions have been reported with other polyacrylamide hydrogel products.
Tonbul M et al. Case Reports in Orthopedics
These reports involved different products and should not be directly extrapolated to Arthrosamid.
Which Knee Injection is Best?
There is no single injection that works best for every patient.
Choice depends on:
- severity and "phenotype" of osteoarthritis
- age and activity level
- patient preference
- cost considerations
- clinician experience
| Injection | Duration | Evidence | Advantages | Limitations | Cost per injection (approx) |
|---|---|---|---|---|---|
| Corticosteroid | weeks - 6 months | Strong for short-term relief | Inexpensive, rapid relief | Short duration in some | < $50 |
| Hyaluronic Acid | 9-15 months | Mixed evidence | Safe, resorbable | Modest average benefit | >$500 |
| PRP | months- 1 year | Variable but promising | Biologic treatment | Variability between protocols | $300 to >$1000 |
| Arthrosamid | years (data to 5 yrs) | Emerging evidence | Single injection, long duration | Permanent implant, expensive | $4,500 |
Who may consider Arthrosamid?
Arthrosamid may be considered for patients who:
- have knee osteoarthritis causing persistent pain
- wish to delay knee replacement surgery
- have not improved with physiotherapy and exercise
- prefer a longer-acting injection.
However, the benefits, cost and uncertainties should be discussed carefully.
Take-Home Points
• knee injections can reduce pain and improve function in osteoarthritis
• corticosteroid injections provide short-term relief
• PRP may provide longer benefits in some patients
• hyaluronic acid evidence is mixed
• Arthrosamid is a
permanent hydrogel implant with emerging evidence
For selected patients it may offer longer-lasting relief, but the long-term safety and effectiveness beyond several years continue to be studied.
Specialist Osteoarthritis Assessment
If you are experiencing persistent joint pain or osteoarthritis, a detailed assessment can help determine the most appropriate treatment options.
At Progressive Sports Medicine, we provide comprehensive evaluation of:
- joint structure
- biomechanics
- muscle strength
- metabolic health
to develop an individualised management plan.
Medical Disclaimer
This article is intended for educational purposes only and does not constitute medical advice. Individual treatment decisions should always be discussed with a qualified healthcare professional. Progressive Sports Medicine has no commercial relationships with pharmaceutical companies or manufacturers of pentosan products.
Scientific References:
Bennell, K.L., Paterson, K.L., Metcalf, B.R., et al. (2021)
Effect of intra-articular platelet-rich plasma vs placebo injection on pain and medial tibial cartilage volume in patients with knee osteoarthritis: a randomised clinical trial. JAMA, 326(20), pp.2021–2030.
This randomised placebo-controlled trial found that platelet-rich plasma injections did not significantly improve knee pain or medial tibial cartilage volume compared with placebo at 12 months. The study highlights that PRP outcomes may vary depending on preparation methods and patient selection.
Latourte, A., Rat, A.C., Omorou, A., et al. (2022)
Do glucocorticoid injections increase the risk of knee osteoarthritis progression over 5 years? Arthritis & Rheumatology, 74(8), pp.1343–1351.
This longitudinal cohort study examined whether repeated intra-articular corticosteroid injections were associated with progression of knee osteoarthritis. The authors reported that corticosteroid injections were associated with greater structural progression of osteoarthritis compared with hyaluronic acid injections, raising questions about repeated long-term use.
Felson, D.T. (2020)
Evidence suggests that intra-articular corticosteroids are effective (short term) and safe (long term). Annals of Internal Medicine, 173(9), pp.740–741.
Felson reviewed the available evidence on corticosteroid injections and concluded that intra-articular corticosteroids can provide meaningful short-term pain relief, while available long-term data suggest they remain generally safe when used appropriately, particularly when injections are not given excessively frequently.
Henriksen, M., Christensen, R., Klokker, L., et al. (2018)
Intra-articular 2.5% polyacrylamide hydrogel for the treatment of knee osteoarthritis: an observational proof-of-concept cohort study. Clinical and Experimental Rheumatology, 36(6), pp.1082–1085.
This early clinical study reported significant improvements in pain and function following injection of polyacrylamide hydrogel, supporting further investigation of the treatment.
Bliddal, H., Beier, J., Hartkopp, A., et al. (2024)
Polyacrylamide hydrogel versus hyaluronic acid for the treatment of knee osteoarthritis: a randomised controlled study. Clinical and Experimental Rheumatology.
This randomised study found polyacrylamide hydrogel injections were non-inferior to hyaluronic acid injections in improving symptoms of knee osteoarthritis at one year.
Bliddal, H., Beier, J., Hartkopp, A., et al. (2025)
Three-year follow-up from a randomised controlled trial of a single intra-articular polyacrylamide hydrogel injection in subjects with knee osteoarthritis. Clinical and Experimental Rheumatology.
The three-year extension study showed sustained improvements in pain and function in patients treated with polyacrylamide hydrogel.
Bliddal, H., Beier, J., Hartkopp, A., et al. (2026)
Sustained symptom relief and safety over five years following a single intra-articular injection of 2.5% polyacrylamide hydrogel in patients with knee osteoarthritis. Clinical and Experimental Rheumatology.
Five-year follow-up data suggested long-term improvement in symptoms, although the study lacked a concurrent control group.
Christensen, L.H., Breiting, V.B., Aasted, A., et al. (2016)
Synovial incorporation of polyacrylamide hydrogel after injection into normal and osteoarthritic animal joints. Osteoarthritis and Cartilage, 24(11), pp.1996–2003. doi:
Preclinical research demonstrated that polyacrylamide hydrogel becomes integrated into synovial tissue, supporting the concept of long-term intra-articular residence.
Christensen, L.H. and Daugaard, S. (2016)
Histological appearance of the synovial membrane after treatment of knee osteoarthritis with polyacrylamide gel injections. Journal of Arthritis.
Histological analysis suggested polyacrylamide hydrogel integrates with the synovial lining and does not appear to provoke aggressive inflammatory reactions in examined tissue samples.
Tonbul, M., Adas, M., Bekmez, S., et al. (2014)
Intra-articular polyacrylamide hydrogel injections are not innocent: a case report. Case Reports in Orthopedics.
This case report described a significant inflammatory reaction following injection of another polyacrylamide hydrogel product, highlighting the importance of ongoing safety monitoring for permanent intra-articular materials.
American Academy of Orthopaedic Surgeons (AAOS) (2021)
Management of osteoarthritis of the knee (non-arthroplasty): clinical practice guideline.
The AAOS guideline concludes that corticosteroid injections may provide short-term symptom relief, while routine use of hyaluronic acid injections is not recommended due to inconsistent evidence.
Kolasinski, S.L., Neogi, T., Hochberg, M.C., et al. (2020)
2019 American College of Rheumatology/Arthritis Foundation guideline for the management of osteoarthritis of the hand, hip and knee. Arthritis Care & Research, 72(2), pp.149–162.
