Hyaluronic Acid Injections for Knee Arthritis

Hyaluronic acid (HA) injections — often called viscosupplementation — have been used for knee osteoarthritis for over thirty years. The treatment is well-established, broadly safe, and has a recognised role in modern knee care. Like all injections for arthritis, it works for the right patient and disappoints when used for the wrong one. This article explains what HA does, the evidence base, and where it fits between conservative care and more invasive options.

What is hyaluronic acid?

Hyaluronic acid is a naturally occurring component of joint fluid (synovial fluid). It contributes to the joint’s lubricating and shock-absorbing properties. In osteoarthritis, the concentration and quality of joint hyaluronic acid is reduced. Viscosupplementation aims to restore some of this lost fluid environment by injecting a high-molecular-weight hyaluronic acid preparation directly into the joint.

How it’s given

HA is injected into the knee in a single visit or a course of 3–5 weekly injections, depending on the specific product used. Modern single-shot products give similar outcomes to the older multi-injection regimens. Injection is performed under sterile conditions, sometimes with ultrasound guidance.

What the evidence shows

Meta-analyses of randomised controlled trials show:

• Modest but real pain relief and functional improvement in mild to moderate knee osteoarthritis, lasting 4–6 months on average
• Greatest benefit in patients with early to moderate disease and a clear inflammatory component
• Limited benefit in end-stage bone-on-bone arthritis
• Onset of effect is slow — typical full effect takes 4–6 weeks

Compared to cortisone, HA gives slower onset but longer-lasting relief. Compared to PRP, head-to-head studies suggest PRP may give greater pain relief and longer duration in early arthritis; both remain reasonable options.

Who benefits most

The ideal candidate is a patient with mild to moderate knee arthritis, mechanical symptoms but not significant deformity, who has tried conservative management without enough relief and who wants to delay or avoid surgery. Patients with very advanced arthritis are unlikely to benefit and are usually better served by other approaches.

Safety

HA is well tolerated. The most common side effect is a transient local reaction with warmth and mild swelling for 1–3 days. Serious complications are rare.

Where HA fits in the wider plan

HA injections are one tool in a stepped approach to knee arthritis. They are most effective when combined with weight management, structured strengthening, activity modification, and judicious use of oral analgesics. A repeat course every 6–12 months is reasonable for responders. When HA stops providing relief, that often signals the time to consider surgical options.