Hyaluronic Acid Knee Injections: Who Benefits, How Long?

Hyaluronic Acid Knee Injections: Who Benefits, How Long?

What is a hyaluronic acid knee injection, who may benefit, how is it done and how long does it last? The evidence, side effects, aftercare and why the cost varies from patient to patient.

A hyaluronic acid knee injection is placed inside the knee joint to temporarily support the slippery, cushioning qualities of the joint fluid. It is mainly considered for mild to moderate knee osteoarthritis. Any effect usually starts within a few weeks and, in people who respond, may last several months. However, not everyone responds, the research results are mixed, and the injection does not rebuild worn cartilage.

This article explains how these injections, often called "gel shots" or viscosupplementation, work, who they may and may not suit, how the procedure is done, how long the effect lasts, the possible side effects and why the cost varies between patients.

What is hyaluronic acid and what does it do in the knee?

Hyaluronic acid is a natural molecule produced by the joint lining that gives joint fluid its thick, slippery consistency. In a healthy knee this fluid lets the cartilage surfaces glide smoothly and acts like a shock absorber under load. In osteoarthritis, both the amount and the structure of hyaluronic acid change, so the fluid becomes thinner and less protective.

Injected hyaluronic acid aims to support these properties for a while and to calm inflammation within the joint. One common misunderstanding is worth correcting: the injection does not "replace lost fluid" or reverse cartilage wear. Its purpose is to reduce pain so that movement and exercise become easier.

Who might it suit?

• People with mild or moderate arthritis on X-ray whose pain continues despite exercise, weight control and medication
• Patients for whom cortisone is less suitable, for example because of diabetes
• People who cannot take painkillers long term because of stomach, kidney or heart problems
• Patients who are not yet candidates for surgery, or who wish to delay it, and want symptom control

In advanced, bone-on-bone arthritis or when the knee is clearly deformed, benefit is less likely, and options such as osteotomy or joint replacement may need discussing. For background on symptoms and stages, read what is knee osteoarthritis?

Who should not have it?

• Anyone with an active infection in the knee or in the skin over the injection site
• People allergic to the product (some products are animal-derived; tell your doctor about egg or poultry allergies)
• People whose pain comes from outside the joint, such as bursitis, tendon problems or pain referred from the hip

People on blood thinners, those with blood disorders and pregnant women need a separate assessment first.

What does the evidence say?

Although hyaluronic acid injections have been used for many years, their effectiveness is still debated. Some studies and analyses show a small but measurable reduction in pain compared with placebo, while others question whether that difference is large enough to matter in daily life. Some international orthopedic and rheumatology guidelines advise against routine use, while others say it can be considered in selected patients.

In practice, some patients describe clear relief while others notice no change, and there is no reliable way to predict who will respond. Hyaluronic acid should be seen as a complement to an exercise program, not a replacement, approached with realistic expectations.

How is the injection done?

1. The skin around the knee is cleaned with antiseptic.
2. If the knee is noticeably swollen, the excess fluid may first be drained with a fine needle.
3. The hyaluronic acid is injected into the joint; ultrasound guidance is used when needed to confirm accurate placement.
4. A small plaster is applied, and you can walk out shortly afterwards.

Products differ in molecular structure and concentration, so some are given as a single injection and others as a series of three to five weekly injections. Your doctor will choose the product and schedule.

Aftercare

• Avoid long walks, running, heavy lifting and demanding sport for the first 24–48 hours; normal walking is fine.
• If the site is sore or swollen, use a towel-wrapped ice pack for 15–20 minutes.
• A mild increase in pain for a day or two can happen; steadily worsening pain is not normal.
• Return to physiotherapy and home exercises when your doctor advises.

When does it start working and how long does it last?

Hyaluronic acid does not act as quickly as cortisone. In responders, relief usually builds gradually over a few weeks and may last several months, although this varies. If the first course helped meaningfully, a repeat may be considered when pain returns, after medical review. If it did not help at all, repeating the same treatment is usually of limited value.

Why exercise still matters

Any period of relief after the injection is a good opportunity to strengthen the muscles around the knee. As the quadriceps and hip muscles get stronger, load on the joint is spread more evenly. Keeping up the program your physiotherapist recommends, rather than stopping once pain eases, may help you maintain better function after the injection wears off. Losing excess weight also reduces the load the knee carries.

Is it used in the hip or other joints?

Hyaluronic acid is sometimes used in the hip, ankle or shoulder, but the evidence in these joints is weaker than in the knee. Because the hip lies deep, injections there are usually done under ultrasound or X-ray guidance. Hip pain can also come from problems such as a labral tear or impingement, so a thorough assessment is needed first.

Possible side effects

• Temporary pain, swelling, warmth or bruising at the injection site
• A flare of pain and swelling lasting a day or two
• Rarely, a marked inflammatory reaction in the joint that can mimic infection
• Very rarely, joint infection or an allergic reaction

Why does the cost vary?

Cost is one of the most common questions. In line with health advertising rules we do not publish prices, but it helps to know why there is no single figure: the type and concentration of the product, single versus multiple injections, whether ultrasound guidance is needed and whether one or both knees are treated all affect the total. Most importantly, whether the injection is suitable for you should be decided by examination and imaging; in the wrong patient it will not deliver the hoped-for benefit, whatever it costs.

When should you see an orthopedic surgeon?

• Knee pain lasting several weeks despite exercise and home measures
• Recurrent swelling, morning stiffness and a shrinking walking distance
• Locking, giving way or being unable to straighten the knee fully
• Previous injections that seem to work for shorter and shorter periods

Urgent: worsening pain, redness, warmth and swelling with fever in the days after an injection may signal infection and need same-day assessment.

At Prof. Dr. Gökhan Polat's clinic, injection decisions are based on the examination, X-ray findings, the stage of arthritis, other health conditions and the patient's expectations. For other non-replacement options, see alternative treatment methods to prosthetic surgery, and for our approach to biological treatments, our cellular therapies (PRP, stem cell) page. Response to treatment varies from person to person.

Summary

• Hyaluronic acid injections aim to support joint fluid temporarily and are mainly considered in mild to moderate knee arthritis.
• Effects start over a few weeks and may last several months in responders; not everyone responds and the evidence is mixed.
• The injection does not rebuild cartilage and should be combined with exercise and weight control.
• Increasing pain, redness and fever after an injection need prompt assessment.

This article is for general information only; diagnosis and treatment decisions are made individually after examination and the necessary tests.