Knee Injections:
"Regenerative" vs. Non-Regenerative
There are injections that merely control symptoms — and injections commercially labelled as "regenerative", which attempt to modify the biology of the knee. Understanding this distinction, and its real limits, is essential to making an informed decision.
Group 1
"Regenerative" Injections
A commercial and scientific label for substances that act on the joint microenvironment — potentially reducing inflammation in a more sustained way, improving lubrication or influencing cartilage metabolism. They do not rebuild destroyed cartilage.
- ✦They act on joint biology, not just on symptoms
- ✦Longer-lasting effects, but with a more gradual onset
- ✦Lower risk of joint deterioration with repeated use
- ✦Best candidates: mild to moderate knee osteoarthritis, tendinopathies
Group 2
Non-Regenerative Injections
They suppress inflammation rapidly and powerfully, but with no disease-modifying effect. They are a tool for symptomatic control — valuable in certain contexts, but with clear limitations.
- ▸Rapid relief — effect within 24 to 72 hours
- ▸Temporary effect: weeks to a few months
- ▸Repeated use may deteriorate the articular cartilage
- ▸Best candidates: acute inflammatory flares, preparation for surgery
How it works
A small sample of the patient's blood is centrifuged to concentrate the platelets. This preparation — rich in growth factors (PDGF, TGF-β, VEGF) — is injected into the joint, creating an anti-inflammatory and pro-anabolic environment that may reduce chronic synovitis and influence cartilage metabolism. There is no evidence of reconstruction of lost cartilage.
What to expect
- Initial analgesic effect in the first few weeks
- Peak efficacy between the 6th and 12th week
- Average duration: 6 to 12 months (varies with the degree of osteoarthritis)
- Usual protocol: 1 to 3 injections at intervals of 2 to 4 weeks
Main indications
Knee osteoarthritis grade I–III
Patellar tendinopathy
Cartilage injuries
After arthroscopic surgery
Safety profile
- Autologous product — no risk of systemic allergic reaction
- Local pain/swelling may occur within 48–72h after injection
- Does not deteriorate the cartilage with repeated use
- No interaction with oral anticoagulants in most protocols
Evidence: Recent meta-analyses (NEJM, JBJS) confirm the superiority of PRP over hyaluronic acid and placebo in mild to moderate knee osteoarthritis, with a statistically significant benefit at 12 months. The quality of the PRP (platelet concentration, leucocytes) and patient selection determine the outcome.
How it works
Hyaluronic acid (HA) is a natural component of synovial fluid. In osteoarthritis, its concentration and viscosity decrease. The injection of exogenous HA restores the viscoelastic properties of the joint fluid, reducing friction and improving cushioning. It also exerts an indirect anti-inflammatory effect via CD44 receptors. It does not regenerate cartilage, but may slow its degradation in some contexts.
What to expect
- Gradual effect: 4 to 8 weeks after the last injection
- Duration: 6 to 12 months (high molecular weight formulations)
- Protocol: 1 injection (cross-linked formulations) or 3–5 weekly
- Repetition possible without joint deterioration
Main indications
Knee osteoarthritis grade I–III
Early cartilage injuries
Patient not a candidate for corticosteroid
Adjunct to physiotherapy
Available types
- Low molecular weight (e.g. Ostenil) — 3 to 5 weekly injections
- High molecular weight cross-linked (e.g. Durolane, Monovisc) — single dose
- Formulations combined with PRP — emerging protocol
Evidence: The ESCEO (European Society for Clinical and Economic Aspects of Osteoporosis) and EULAR include viscosupplementation in their knee osteoarthritis guidelines. Efficacy varies with the degree of osteoarthritis and the molecular weight of the formulation. Advanced knee osteoarthritis (grade IV) responds less well. The combination with PRP shows promising preliminary results.
How it works
Intra-articular corticosteroids suppress the inflammatory cascade via glucocorticoid receptors in the synovial cells — inhibiting prostaglandins, pro-inflammatory cytokines (IL-1β, TNF-α) and pain mediators. The result is a rapid and powerful reduction in synovitis and joint effusion.
What to expect
- Relief within 24 to 72 hours after the injection
- Maximum effect: 1 to 2 weeks
- Duration: 4 to 8 weeks (varies between patients)
- Recommendation: maximum 3 to 4 injections per joint per year
Main indications
Acute inflammatory flare
Synovitis with effusion
Preparation for an event
Symptomatic advanced knee osteoarthritis
Risks and limitations
- Repeated use associated with loss of articular cartilage (MRI studies)
- May mask the progression of the underlying disease
- Increased risk of joint infection in diabetic patients (transient)
- Not to be used in patients planning a knee replacement within the following 3 months
- Post-injection "flare" in 2–10% of cases (pain in the first 48h)
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Important clinical note: Longitudinal MRI studies (Raynauld et al., NEJM; McAlindon et al., JAMA 2017) demonstrated greater loss of cartilage volume at 2 years in patients with knee osteoarthritis who received repeated corticosteroid injections vs. saline. This finding does not invalidate their use, but it should guide patient selection and the frequency of administration.
| Parameter |
Corticosteroid |
Hyaluronic Acid |
PRP |
| Type |
Non-regenerative |
"Regenerative" |
"Regenerative" |
| Onset of effect |
24–72 hours |
4–8 weeks |
4–12 weeks |
| Duration of effect |
4–8 weeks |
6–12 months |
6–12+ months |
| Effect on cartilage |
Potentially negative |
Neutral / protective |
No regeneration; may slow degradation |
| No. of injections |
1 |
1–5 (depending on product) |
1–3 (protocol) |
| Repeated use |
Limited (<4/year) |
Safe |
Safe |
| Best indication |
Acute flare, synovitis |
Mild-to-moderate chronic knee osteoarthritis |
Knee osteoarthritis + active injury |
| Pre-surgical use |
Avoid in the 3 months before |
No contraindication |
May accelerate recovery |
Which one is right for your case?
Every clinical situation is different. These scenarios illustrate the reasoning, but the final decision is always made after assessment.
Scenario A
"I have had severe pain for 3 days, my knee is swollen and I want rapid relief."
Acute inflammatory flare with synovitis. The corticosteroid is the most appropriate option for rapid control of symptoms.
→ Corticosteroid
Scenario B
"I have grade II knee osteoarthritis. The pain is chronic and I want to avoid surgery."
Chronic disease without an acute flare. PRP or hyaluronic acid (depending on the degree of injury and the patient's profile) are the first-line options.
→ PRP or Hyaluronic Acid
Scenario C
"I have patellar tendinopathy. I have already tried physiotherapy for 3 months without improvement."
Refractory chronic tendinopathy. PRP has the best evidence in this context. Corticosteroids are contraindicated in tendons (risk of rupture).
→ PRP
Scenario D
"I am having knee surgery in 6 months. Can I have an injection to manage the pain in the meantime?"
Avoid corticosteroids in the 3 months preceding surgery (increased infection risk). Hyaluronic acid or PRP are safe alternatives.
→ Hyaluronic Acid or PRP
1
Assessment
Confirmation of the indication, review of imaging tests, exclusion of contraindications.
2
Preparation
Strict asepsis. Positioning of the knee. Ultrasound-guided whenever indicated for greater precision.
3
Injection
A procedure of 2 to 5 minutes. Minimal discomfort. Aspiration of effusion if present.
4
Post-procedure
Relative rest for 24–48h. Resumption of usual activity in 2 to 3 days. Scheduled follow-up.
Will the injection cure my osteoarthritis?
No injection cures osteoarthritis — it is a chronic degenerative disease with no known definitive cure (other than knee replacement). What injections can do is control the symptoms, slow the progression (especially PRP and HA) and improve quality of life. The aim is to manage osteoarthritis over the long term, not to eliminate the disease.
Can I have corticosteroids repeatedly if they help me?
This is one of the most important questions in clinical practice. Corticosteroids are effective in the short term, but long-term MRI studies show loss of cartilage volume with repeated use. The current recommendation is not to exceed 3 to 4 injections per joint per year, and to explore so-called "regenerative" alternatives — PRP or hyaluronic acid — for chronic pain control.
Is PRP reimbursed by the NHS or by health insurance?
In Portugal, PRP is currently not reimbursed by the public health service (SNS) for knee osteoarthritis. Some private health insurance plans cover it partially, but this varies with the policy. Hyaluronic acid is reimbursed by the SNS under certain conditions. Intra-articular corticosteroid is widely reimbursed. I recommend confirming coverage with your insurer before the appointment.
Can I have an injection and then have knee surgery?
It depends on the type. Intra-articular corticosteroids increase the risk of peri-surgical infection — the recommendation is a minimum interval of 3 months before any joint surgery. Hyaluronic acid and PRP do not have this contraindication. It is essential to inform the surgeon of any recent injection before an operation.
I have diabetes. Can I have a corticosteroid injection?
Yes, but with caution. Intra-articular corticosteroids may cause a transient rise in blood glucose in the 24 to 72 hours after the injection — especially in diabetics with less rigorous control. The risk is real but generally manageable. Always inform your doctor about the state of your diabetes. In diabetic patients with chronic knee osteoarthritis, the so-called "regenerative" options — PRP or hyaluronic acid — are often preferable for repeated use.
What is the difference between the brands of hyaluronic acid (Ostenil, Durolane, Monovisc)?
The main difference lies in the molecular weight and the presence or absence of cross-linking (cross-links between HA chains). High molecular weight cross-linked products (Durolane, Monovisc) are administered in a single injection and have a longer theoretical duration. Low molecular weight products (Ostenil) require 3 to 5 weekly injections but have a lower unit cost. The choice depends on the degree of osteoarthritis, patient preference and the clinical context.
Want to know which injection is right for your knee?
The correct selection depends on the diagnosis, the degree of osteoarthritis, the clinical history and your objectives. Book an appointment for an individualised assessment.
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