Injection Therapies for Knee Osteoarthritis: A Review of the Evidence

A review of current evidence on injection therapies for knee osteoarthritis finds most offer limited or uncertain long-term benefit, with no treatment shown to repair the joint. Guidelines conditionally recommend only corticosteroid injections for short-term pain relief during flare-ups, while other common injections are not recommended.

Guidelines conditionally recommend only corticosteroid injections for short-term pain relief during flare-ups, while other common injections are not recommended.

Condition Overview and Prevalence

Knee osteoarthritis is a condition affecting the entire joint, including bone, cartilage, ligaments, and muscles. It is a common cause of pain and movement difficulty. In Australia, 8.3% of people are reported to be affected by the condition.

Assessment of Injection Treatments

Clinics commonly offer four types of injections for knee osteoarthritis pain: corticosteroids, hyaluronic acid, platelet-rich plasma (PRP), and stem cells. The evidence for each varies.

• What they are: Anti-inflammatory medications.
• Guideline Position: Conditionally recommended for short-term relief during pain flare-ups.
• Evidence: A 2024 systematic review found meaningful benefits primarily in the first few weeks, with effectiveness diminishing after approximately six weeks. One trial found that injections administered every three months over two years did not improve pain and were associated with greater cartilage loss compared to a placebo.
• Recommendation: Guidelines recommend cautious use for short-term relief rather than ongoing treatment.

• What they are: A substance naturally found in joint fluid; injections aim to improve lubrication.
• Guideline Position: Not recommended for knee osteoarthritis.
• Evidence: A large systematic review concluded benefits are small and unlikely to be meaningful. The review also found a higher risk of serious adverse events compared to placebo.

• What they are: Injections using a person's own blood, processed to concentrate platelets, which contain growth factors.
• Guideline Position: Not currently recommended.
• Evidence: Systematic reviews report varying findings, with some showing benefits and others finding weak effects compared to placebo. Some larger, rigorous trials show little or no benefit. A key limitation is the lack of standardization in preparation methods and concentrations across clinics. There is no evidence that PRP injections repair or regrow joint cartilage.
• Cost: Typically ranges from A$300–$900 per injection, or up to $2,700 for a course of three.

• What they are: Cells promoted as a way to regenerate damaged tissue, which can be sourced from a person's own body or from donor cells.
• Guideline Position: Recommended against due to limited evidence, high costs, and regulatory concerns.
• Evidence: A recent Cochrane review found stem cell injections may provide small improvements in pain and function, but the results were uncertain and based on low-quality evidence. No published studies have evaluated whether they repair cartilage or change osteoarthritis progression. More high-quality research is underway.
• Cost: Often $5,000 or more per injection.

Limitations of the Evidence Base

Research on injection therapies faces several challenges:

• Many existing studies are small or of low quality.
• Placebo effects are particularly large with injections, meaning studies without proper controls may overestimate benefits.
• For PRP and stem cell injections, variable methods used across clinics complicate the interpretation of results.

Recommended Treatments with Stronger Evidence

Treatments for knee osteoarthritis that are supported by high-quality evidence include:

• Any type of exercise.
• Weight loss, if appropriate.
• Over-the-counter medications, such as the short-term use of anti-inflammatories.

These approaches are generally considered safe and are less expensive than injections.

General Considerations for Injection Therapies

Key points for individuals considering injections include:

• All joint injections carry a small risk of infection.
• The exact mechanism of action for some injections is unclear.
• Some reported benefits may be related to placebo effects.
• For corticosteroids, any reduction in pain should become apparent within six weeks.