Molecular Weight
The size of a molecule measured in daltons. In hyaluronic acid products, molecular weight affects how thick and long-lasting the injection is, with higher molecular weight typically providing longer relief.
Extended Definition
Molecular weight (MW) is a critical property that distinguishes different hyaluronic acid (HA) products used for viscosupplementation. It refers to the mass of a molecule, measured in units called daltons (Da). For HA products, molecular weight typically ranges from about 500,000 Da to over 6 million Da.
The molecular weight of hyaluronic acid significantly influences its behavior in the joint. High molecular weight HA (typically above 1-2 million Da) forms longer molecular chains that create a thicker, more viscous gel. These larger molecules tend to remain in the joint longer and may provide more cushioning effect. Products like Synvisc and Synvisc-One use high molecular weight HA. Lower molecular weight HA (under 1 million Da) produces a thinner solution that may penetrate tissues more easily but may be broken down more quickly by the body.
Some products use cross-linked hyaluronic acid, where HA molecules are chemically bonded together to create even larger, more stable structures. This can further extend the duration of effect. However, the relationship between molecular weight and clinical outcomes isn’t always straightforward—different patients may respond better to different molecular weight formulations. Factors like the degree of joint damage, activity level, and individual body chemistry can all influence which HA product works best. Research comparing different molecular weight HA products shows mixed results, with some studies suggesting advantages for higher MW products in terms of duration of relief, while others show similar effectiveness across different formulations.
Related Terms
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A powerful anti-inflammatory medication similar to cortisol (a hormone naturally produced by the body) that can be injected into joints to quickly reduce swelling and pain.
Hyaluronic Acid
A naturally occurring substance found in synovial fluid that gives it its thick, gel-like consistency and lubricating properties. Also used as an injection treatment for joint pain.
NSAID
Non-Steroidal Anti-Inflammatory Drug - a type of medication that reduces pain, inflammation, and fever by blocking enzymes that produce inflammatory chemicals in the body.
Nerve Block
An injection of anesthetic near specific nerves to temporarily block pain signals. Used for diagnosis, pain relief, or before surgery. Effects last hours to months depending on medication used.
Orthotic
A custom or prefabricated device worn to support, align, or correct joint and limb function. For knee arthritis, includes braces, shoe inserts, and wedged insoles that reduce joint stress.