Knee Injections —
PRP, Gel and Cortisone

What Happens in Knee Arthritis

Knee osteoarthritis occurs when the smooth bearing surface of the joint (articular cartilage) gradually wears out, often accompanied by changes in the underlying bone and the joint lining. As cartilage thins, the knee becomes stiff, painful and swollen, especially with weight-bearing activities like walking, stairs and prolonged standing.

Over time, many patients find that pain limits simple daily tasks such as shopping, housework, or work duties. Sleep can be disturbed by night pain or aching after activity. Exercise and sport are scaled back or abandoned, which can then affect weight, general health and mood.

Most non-operative treatments are designed to reduce pain and improve function, not to rebuild lost cartilage. International guidelines describe knee osteoarthritis care as a continuum, moving from education, exercise and weight management through to joint replacement when symptoms severely impact quality of life.

Hyaluronic Acid (Synvisc, Euflexxa and Similar "Gel" Injections)

Hyaluronic acid (HA) is a lubricant naturally found in joint fluid; commercial preparations such as Synvisc and Euflexxa aim to restore some of that lubrication. Clinical trials and meta-analyses suggest that many patients experience modest pain relief for several weeks to a few months after a series of HA injections. Some studies show benefit over saline placebo, while others show little or no difference at 6–12 months. HA does not appear to regenerate cartilage in arthritic knees; the effect is best described as temporary cushioning and lubrication.

Because improvements are modest and short term, and because costs can be high, several major guidelines now recommend against routine use of HA for knee osteoarthritis. In Australia, recent standards emphasise avoiding low-value care and prioritising effective non-surgical management instead.

Platelet-Rich Plasma (PRP): Biologic, But Still Symptom-Focused

PRP is prepared from your own blood and contains a concentrated mix of platelets and growth factors that theoretically may influence inflammation and cell behaviour in the joint. Over the last decade, many studies have compared PRP to placebo, steroids and HA.

A 2025 meta-analysis of 18 randomised trials (1,995 patients) found that PRP provided better pain and function scores than placebo up to 12 months, with clinically relevant improvements at 3 and 6 months. Earlier studies also show better symptom relief with PRP than with HA in many patients, especially those with milder osteoarthritis. Adverse events are generally mild (such as transient swelling or synovitis) and serious complications appear rare in the short term.

Despite this, current evidence still frames PRP as a symptom-modifying treatment, not a cartilage-regenerating cure. Reviews of cartilage regeneration techniques emphasise that while various injectable biologics, including PRP, can improve pain and function, robust long-term evidence of true structural cartilage regrowth in human knees is lacking. Some imaging studies show subtle changes in cartilage quality, but this has not translated into consistent, durable reversal of arthritis.

Why These Injections Are Best Seen as Temporary Measures

Across steroids, HA and PRP, several themes repeat in high-quality studies. All three are time-limited in their benefit: steroids peak in the first 1–4 weeks and are often gone by 2–3 months; HA offers potential pain reduction over several months, but responses are variable and sometimes indistinguishable from placebo by 6–12 months; PRP in good-quality trials can extend to 6–12 months, but the effect still wanes over time.

No injection has demonstrated proven, durable cartilage regeneration. Human clinical data do not show consistent rebuilding of normal joint cartilage from these injections. Recent reviews of cartilage regeneration research highlight that emerging injectable biomaterials and cell-based therapies are still largely experimental, with promising animal results but limited long-term human evidence.

Guideline positions are also consistent. The OARSI non-surgical management guidelines regard intra-articular steroids as an "appropriate" option for short-term relief, not as a disease-modifying therapy. PRP is considered promising for some patients, but heterogeneity of preparation and lack of long-term structural data mean it is not yet universally recommended as standard of care.

From a patient perspective, it can be helpful to think of these injections as tools that may buy time — months of reduced pain or better function — rather than treatments that repair the underlying mechanical problem of severely worn cartilage.

Injections and Infection Risk Around Knee Replacement

One crucial consideration for anyone contemplating a future knee replacement is infection risk. A deep infection after total knee arthroplasty is a major complication that can require further surgery, prolonged antibiotics, and sometimes removal of the implant.

Large database studies have found that in a cohort of 22,240 patients, an injection into the knee within 3 months before knee replacement doubled the odds of postoperative infection in the first 3 months, and increased infection risk out to 6 months. An analysis of 83,684 knee replacements found that any prior intra-articular injection within the year before surgery was associated with higher infection rates (4.4% vs 3.6%). Injections given within 6 months of surgery carried significantly higher odds of any surgical site infection; when the injection was more than 6 months before surgery, this excess risk was no longer evident. For infections serious enough to need a return to theatre, elevated risk persisted when injections were within 7 months of the knee replacement.

A 2021 focused study on timing of corticosteroid injections suggested that the period of highest risk may be the first 4 weeks after injection, with risk gradually declining thereafter, but still elevated when surgery is performed within 3 months. Taken together, these studies support a cautious approach: avoid intra-articular injections in the 3 months before a planned knee replacement. Many surgeons extend that window to 6 months or more, especially if there are other infection risk factors.

This is an important discussion to have early with your surgeon so that short-term pain relief strategies do not compromise the safety of a future joint replacement.

Non-Operative Management: What Actually Helps

Non-surgical care remains the cornerstone of knee osteoarthritis management at all stages, and international and Australian guidelines are consistent on this point. Steroid, HA and PRP injections, when used, should sit on top of this foundation — not replace it. They can help "take the edge off" symptoms so that you can participate in exercise and everyday life while you and your surgeon monitor progression over time. Key elements of effective non-operative care include the following.

1. Education and self-management. Understanding what arthritis is — and what it is not — reduces anxiety and helps you make informed decisions. Simple strategies such as pacing activities, using handrails on stairs and choosing supportive footwear can make daily life easier.
2. Targeted exercise. Land-based exercise programs focusing on quadriceps and hip strengthening, balance and general aerobic fitness improve pain and function. Both supervised physiotherapy and well-designed home programs are effective; the best program is the one you can stick with long term.
3. Weight management. For people carrying excess weight, even a 5–10% reduction can significantly reduce knee load and symptoms. Diet changes combined with exercise are more effective than diet alone.
4. Simple pain-relief medications. Paracetamol, topical anti-inflammatory gels and short courses of oral anti-inflammatories can help, used carefully and under medical supervision. Other options (such as duloxetine) may be considered for persistent pain in selected patients.
5. Supports and activity modification. Braces, walking aids, or off-loading devices can reduce pain in some patients, particularly with one-sided compartment disease if you can tolerate them. Modifying high-impact activities — for example, substituting deep squats and running with cycling, swimming or elliptical machines — often allows patients to remain active while protecting the knee.

When Knee Replacement Becomes a Good Option

Despite best non-operative care, many people reach a point where knee arthritis dominates daily life. Common signs that a total knee replacement may be appropriate include daily pain that persists despite optimised non-surgical measures and limits walking distance, stairs or work; night pain that disturbs sleep on a regular basis; marked stiffness or deformity with X-rays showing advanced joint space loss; and a feeling that you are planning your day around your knee, rather than your knee fitting into your life.

Current Australian clinical care standards emphasise that joint replacement is a good option when symptoms are severe, non-operative treatments have been trialled, and quality of life is significantly impaired. Modern knee replacement surgery is highly successful for relieving pain and improving function, particularly when performed by high-volume surgeons using contemporary techniques.

From a decision-making point of view, it is helpful to remember that injections (steroid, gel, PRP) are temporary symptom-relief tools with no proven ability to rebuild cartilage or permanently halt arthritis. They should be timed carefully if a knee replacement is likely in the medium term, to avoid raising the risk of infection. When your knee consistently stops you from doing the things that matter to you — work, caring for family, sport or simply enjoying daily life — moving from short-term fixes to a definitive surgical solution becomes a reasonable next step to discuss with your surgeon.

Common Patient Questions