If you have knee pain from osteoarthritis and have been recommended an injection, you probably have many questions: which one is best? Will it hurt? How many can I get? Could they damage my knee? In this article, I explain with updated scientific evidence the differences between the three main options — corticosteroids, hyaluronic acid, and PRP — so you and your doctor can make the best decision.
What is a joint injection?
A joint injection delivers medication directly inside the knee joint. Think of it as bringing treatment exactly where it is needed most, without having to pass through the entire body. It is performed with a thin needle, in the office, and the procedure takes less than one minute.
Corticosteroids: fast relief, strategic use
Corticosteroid injections (commonly betamethasone in Latin America) combine a fast-acting form for immediate relief and a depot form for sustained anti-inflammatory effect over weeks.
How well do they work? A 2024 meta-analysis of 842 patients in controlled clinical trials showed that corticosteroids produce clinically significant pain relief in the short term (up to 6 weeks), but that benefit is lost after 6 months. Corticosteroids are excellent for calming acute inflammatory flares, but are not a medium or long-term solution.
How many can I get? A maximum of 3 to 4 injections per year is recommended, at least 3 months apart. The 2024 scoping review by Pirri et al., analyzing 65 articles on injectable safety, documented that betamethasone can cause cartilage toxicity (chondrotoxicity) at high doses. The key is dosage: at standard doses and proper frequency, the risk is manageable.
Important note on corticosteroid injections
The AAOS conditionally recommends corticosteroids for knee OA. Their strength is rapid relief of acute flares. Their weakness: the effect lasts only 2-6 weeks and frequent use may deteriorate cartilage. Use them strategically, not as chronic treatment.
Hyaluronic acid: lubrication, protection and time gained
Injected hyaluronic acid (HA) works as a joint lubricant that replicates the synovial fluid your knee has lost. But saying it "only lubricates" falls short: the latest evidence demonstrates that hyaluronic acid has biological effects that go beyond simple lubrication.
What the evidence shows in favor of hyaluronic acid
Pain reduction: a 2024 meta-analysis with 3,851 patients showed significant improvement in WOMAC pain and stiffness scores at 2-8 weeks compared to placebo. A 2025 umbrella review found that 20 of 22 reviews reported significant beneficial effects on pain and function.
Cartilage protection (chondroprotection): unlike corticosteroids — which have been associated with greater osteoarthritis progression and joint space narrowing — hyaluronic acid has demonstrated protective effects on cartilage. At the molecular level, HA binds to CD44 receptors on chondrocytes, stimulating endogenous production of hyaluronic acid and proteoglycans, while reducing metalloproteinases (the enzymes that degrade cartilage). Imaging studies have correlated HA injections with less cartilage deterioration compared to corticosteroids and untreated controls.
Delaying knee replacement surgery: a study with data from thousands of U.S. patients showed that those receiving hyaluronic acid took an average of 484 days to need knee replacement, compared to 114 days for non-recipients. Patients completing 5 or more HA courses delayed surgery an average of 3.6 years, compared to 0.7 years for non-users.
Molecular weight matters: high molecular weight (HMW) formulations show superior results: 57% responder rate vs. 34% for low molecular weight, with better anti-inflammatory effect.
Why hyaluronic acid deserves more credit than it gets
The AAOS does not routinely recommend it, but the EUROVISCO 2025 consensus — an expert panel from 7 European countries — does support its use in specific clinical scenarios. The evidence for delaying knee replacement, chondroprotection, and superior safety over corticosteroids gives it an important place in the therapeutic arsenal, especially for patients who are not yet surgical candidates.
PRP: the best medium and long-term evidence
Platelet-rich plasma (PRP) concentrates growth factors from your own blood and is injected into the joint. Accumulated evidence over recent years positions it as the injectable treatment with the best medium to long-term outcomes.
A 2024 meta-analysis with 3,348 patients directly compared PRP vs. corticosteroids vs. hyaluronic acid. PRP was superior to corticosteroids at short, medium, and long-term, and comparable to HA short-term but superior at medium and long-term. A 2024 network meta-analysis of 9,338 knees gave PRP a SUCRA score of 91.5 out of 100, compared to 53.1 for HA and 15.2 for corticosteroids.
The ESSKA-ICRS 2024 consensus granted PRP a Grade A recommendation for mild-to-moderate osteoarthritis (Kellgren-Lawrence grades I-III). This is the highest possible evidence-based recommendation.
Comparative table: three injections head to head
| Parameter | Corticosteroid | Hyaluronic Acid | PRP |
|---|---|---|---|
| Onset of effect | 1-2 weeks | 2-6 weeks | 2-4 weeks |
| Duration of effect | 2-6 weeks | 4-6 months | 6-12 months |
| Protocol | 1 injection; max 3-4/year | 1 injection every 6-12 months | 3 sessions every 1-2 weeks |
| Effect on cartilage | Potential damage with frequent use | Chondroprotective (protective) | No documented damage |
| Delays surgery? | Not demonstrated | Yes (up to 3.6 years with multiple courses) | Not directly evaluated |
| Best for | Acute inflammatory flares | Maintenance, medium-term protection | Best long-term functional outcome |
| Ideal KL grades | I-II (flares) | I-III | I-III |
| Society endorsement | AAOS: conditional | EUROVISCO 2025: yes (with conditions) | ESSKA 2024: Grade A (KL I-III) |
| Relative cost | Low | Moderate | High |
The therapeutic ladder: what to use based on your OA grade
Stepwise approach for knee osteoarthritis
When are injections no longer enough?
Persistent pain >6/10
Despite 2+ complete injection courses in the last 12 months.
Severe functional limitation
Unable to walk more than 500 meters, climb stairs, or perform daily activities.
Grade IV OA on X-ray
Complete joint space loss with bone-on-bone contact. Injections have minimal yield.
No WOMAC improvement
If you don't improve at least 9 points on the WOMAC scale after adequate treatment.
For more information on which therapies actually repair cartilage and which don't, read our article on cartilage repair: myths and truths.
Looking for exercises for this condition?
We have step-by-step rehabilitation guides with illustrated exercises and evidence-based protocols.
View guide: Grade IV Osteoarthritis →View guide: Chondromalacia →
Frequently asked questions
Does a knee injection hurt?
Most patients describe mild, brief discomfort during application. Local anesthetic is used and ultrasound-guided technique improves precision and reduces pain. The entire procedure takes less than one minute.
How many corticosteroid injections can I get per year?
A maximum of 3 to 4 corticosteroid injections per year is recommended, with at least 3 months between each one. More frequent injections have been associated with increased cartilage deterioration on imaging studies.
Can hyaluronic acid delay knee replacement surgery?
Yes. A study with data from thousands of patients showed that those who received hyaluronic acid took an average of 484 days to need knee replacement, compared to 114 days for non-recipients. With 5 or more courses, the average delay was 3.6 years.
Can hyaluronic acid and PRP be combined?
Yes. Recent studies show that combining hyaluronic acid with PRP produces better pain and function outcomes than either alone, at 3, 6, and 12 months follow-up. Their biological mechanisms are complementary.
How long do knee injections take to work?
Corticosteroids act within 1-2 weeks with peak relief at 2-4 weeks. Hyaluronic acid improves gradually over 2-6 weeks. PRP begins working in 2-4 weeks and progressively improves over 8-12 weeks.
When are injections no longer enough and surgery is needed?
When pain persists above 6/10 despite 2 or more injection courses, functional limitation is severe, or X-rays show grade IV osteoarthritis, it is time to evaluate surgical options such as arthroscopy, osteotomy, or knee replacement.
Not sure which injection is right for you?
A clinical evaluation with X-rays can determine your osteoarthritis grade and the best treatment for your case — with no generic prescriptions.
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