Hyaluronic acid injections are used to treat knee osteoarthritis and improve the functions of the knee joint. This treatment method is called viscosupplementation.
During a hyaluronic acid injection (viscosupplementation), a small amount of hyaluronic acid, often just 2 mL, is injected directly into the knee joint capsule.1
The goals of treating knee osteoarthritis with hyaluronic acid injections are to:
- Reduce pain
- Improve joint movement by increasing joint lubrication and reducing joint friction and inflammation
- Perhaps slow osteoarthritis progression
Hyaluronic acid injections are usually given at a doctor’s office. Depending on the brand used, this treatment involves 1, 3, 4, or 5 injections. If more than one injection is needed, injections are given one week apart.2
What Does Hyaluronic Acid Do in the Knee Joint?
A healthy knee joint contains up to 4 mL of joint fluid.3 Hyaluronic acid is a key component of the joint fluid. It gives the joint fluid its viscous, slippery quality, which does the following:
- Enables the bones' cartilage-covered surfaces to glide against each other, thereby reducing joint friction
- Adds cushion to protect joints during impact (e.g. weight-bearing activity)
See Knee Anatomy
Joints affected by osteoarthritis typically have a lower concentration of hyaluronic acid in their joint fluid than healthy joints, and therefore less protection against joint friction and impact.4 Experts believe this further accelerates the joint degeneration process, setting in place a vicious cycle.
Who Can Get Hyaluronic Acid Injections for Knee Osteoarthritis?
Hyaluronic acid injection is not a first-line treatment for knee osteoarthritis.5 This treatment may be considered for those who:
- Have moderate knee osteoarthritis with symptoms that affect daily living.6-7
- Do not take pain medication because they:
- Have little or no benefit from pain relieving medications, such as non-steroidal anti-inflammatory drugs (NSAIDs), and/or steroids (tablets or injectable).4-5 Some people may also choose to avoid these medications.
- Are at a risk of side effects such as kidney damage, heart problems, and/or abdominal bleeding with long-term use of NSAIDs.5,6,8
- Have other conditions, such as diabetes or high blood pressure, and cannot take medications such as steroids.
- Show improvement after the first round of treatment. Such cases may benefit from additional hyaluronic acid injections when the osteoarthritis symptoms reappear.5-6
- Are not eligible for surgery, want to postpone surgery, or do not want to have surgery.
While people of any age can get hyaluronic acid injections, this treatment may be more effective in people under 65 years of age.2
When Are Hyaluronic Acid Injections Not Appropriate?
Hyaluronic acid injections may not be appropriate in some people, including, but not limited to:
- Women who are pregnant or breast-feeding.2
- Children and adolescents.2
- Those with bacterial and other infections in and/or around the osteoarthritic knee.2
- Those with a known allergy to hyaluronate products.2
Additionally, those who are allergic to eggs or other bird products (e.g. poultry) are advised to inform their doctor.4 This is because certain hyaluronate products are made from rooster combs and may not be suitable for such patients.
Questions to Ask When Choosing Hyaluronic Acid Injection Treatment for Knee Osteoarthritis
While deciding to choose hyaluronic acid injections for the knee, it may help to ask the doctor a few questions regarding the treatment. Asking relevant questions will help weigh the potential risks and benefits of these injections and set reasonable expectations.
A few examples of questions that can be asked are:
- What is the typical outcome for a patient like me?
- Will there be an immediate reaction in my knee after the injection?
- What are the risks associated with this injection?
- How long will my recovery be?
- Is it recommended to take time off work?
- How might this injection affect the chances of postponing my knee replacement surgery?
- Do I need to do anything to prepare for the injection?
- What other treatments can be considered?
By asking these questions, patients can discuss concerns specific to their health and lifestyle and make the necessary adjustments for a better treatment outcome.