Hyaluronic acid is a natural component that occurs within synovial fluid. It helps to lubricate the joint, increases viscosity, and helps to protect the joint by providing shock absorption. As the knee starts to degenerate or we succumb to injury, the relative concentration of hyaluronic acid within our synovial fluid begins to decrease. As a result of this, we are more prone to injury, our shock absorption is reduced, and we may encounter pain.

How Do They Work?

Hyaluronic acid injections, also called viscosupplementation, directly affect the concentration of hyaluronic molecules within your joint fluid. By injecting this viscous supplementation, we are aiming to increase the shock absorbing capacity of your synovial fluid, improve the lubrication of the joint, and therefore, reduce your pain and improve joint mobility.

How Can It Help Joint Arthritis

Knee osteoarthritis is often triggered by defects in the cartilage or subchondral bone. This can happen over a long period of time but can also be brought on by injury. Additionally, metabolic factors such as a sedentary lifestyle and being overweight can contribute to development of osteoarthritis. When osteoarthritis sets in, the joint is more vulnerable to injury, inflammatory processes that are initiated through microtrauma begin to degenerate and injure the articular cartilage and the subchondral bone.

Chondrocytes within the cartilage become metabolically active and begin to secrete inflammatory cytokines that work to stimulate the synthesis of enzymes that begin to break down cartilage. Key cytokines include interleukin-one, tumour necrosis factor and interleukin-six. These commonly increase in inflamed joints and the cytokine activity, which increases inflammation, causes pain, further degeneration, and reduced mobility.

Hyaluronic acid that naturally occurs within your joints is a polysaccharide. It’s produced by the chondrocytes and the synoviocytes within the cartilage. While it is mostly thought of as a physical compound, it also helps to maintain the cartilage matrix and has an influence on inflammation within the knee.

Hyaluronic molecules are measured in molecular weight. This refers to the concentration of hyaluronic acid within the synovial fluid. As the joint progresses towards osteoarthritis, the relative molecular weight of hyaluronic acid reduces resulting in reduced fluid viscosity and elasticity.

What Is The Evidence?

Studies have shown that hyaluronic acid injections increase synovial fluid viscosity by enhancing the molecular weight of HA within synovial fluid. Because of its effect on the cellular matrix of the cartilage, it can also therefore, help to suppress the overall inflammatory cytokine response within osteoarthritis.

Can I Have A Hyaluronic Acid Injection?

Studies have shown that any patient at any stage with osteoarthritis can benefit from having a hyaluronic acid injection. Studies have definitely supported that pain and mobility can improve. However, a period of six weeks to three months is often required for the hyaluronic acid to take effect. There are no contraindications to having a HA injection and patients who have previously had steroid with no effect often feel the benefit of HA injections.

How Is It Injected?

When we assess the knee, we also use an ultrasound scan to survey the knee and establish the best access to the joint.  By using an aseptic no-touch ultrasound-guided technique, the HA can be safely injected into the joint.  It is important to ensure the access to the joint is clear to ensure the injectate is in the joint and not in the surrounding tissue.

How Long Do I Need To Wait Before It Takes Effect?

Some studies have shown that viscosity of fluid tended to increase over a three to six month period, meaning that patients sometimes have to wait a little time and modify their activity for longer before they see a significant reduction in pain. This is because of the way that hyaluronic acid, being a natural substance within the joints, not only has a physical effect, but also has a cumulative effect where it stimulates the production of properties that enable the knee and the synovial fluid to acquire and reestablish fluid viscosity, weight bearing capacity, and inflammatory reduction.

Verdict?

Overall, HA is a sensible option for knee pain with good evidence. However, injections must be coupled with activity modifications, rehabilitation and the passage of at least 3 months to see the full effect of Hyalruonic acid injections.