Viscosupplementation treatment involves supplementing the diminished amount of hyaluronic acid in the diseased joint’s degraded synovial fluid with a hyaluronic acid product that possesses the rheological properties of healthy synovial fluid.
These medications are normally offered as second-line therapies, which are treatments that are used after the patient has not adequately responded to primary treatments such as pain medication and physical therapy. Viscosupplement preparations differ significantly in their molecular weight, concentration, rheological properties, manufacturing processes, and residence times in the joint.
The effects that viscosupplements confer are delayed but long-lasting. While it can sometimes take weeks or even several months for the full results of viscosupplements like Orthovisc and Synvisc to materialize, these medications can provide up to six months of improvement, including reduced pain and a greater range of motion.
As a pharmaceutical class, viscosupplements have been widely studied and consistently shown to be safe and effective for the treatment of knee osteoarthritis. They are widely used and accepted by many doctors and medical practitioners.
Knee Osteoarthritis and Hyaluronic Acid
Osteoarthritis of the knee is a painful degenerative condition of the knee joint in which the gradual breakdown of the protective cartilage around the ends of the bones leads to damage and the gradual destruction of the joint, causing symptoms of inflammation, stiffness, and pain.
Patients with this disease suffer from limited mobility that often interferes with daily activities. Typical strategies to cope with this progressive, degenerative disease include the use of analgesics, physical therapy, and weight loss management, or a combination of the above.
A critical component in the development of osteoarthritis is synovial fluid, the thick, viscous liquid found in synovial joints like the knees that is responsible for the lubrication and cushioning of the bones. Synovial fluid is primarily made up of hyaluronic acid, which provides synovial fluid with its highly viscoelastic properties.
In people with knee osteoarthritis, the quantity and size of the hyaluronic acid molecules in the synovial fluid is reduced, resulting in rheological changes to the fluid itself. The fluid becomes thinner and more watery, reducing its ability to lubricate and cushion the joint.
Orthovisc vs. Synvisc
• Composition: Synvisc injection for a knee is made of a complex of reticulated hylan, hylan A and hylan B. Hylan A is a soluble, high-molecular-weight molecule that comprises 80% of the complex, while hylan B is an insoluble gel-like continuous molecular network that makes up the remaining 20% of the complex. Orthovisc, on the other hand, comprises cross-linked, high-molecular-weight hyaluronan.
• Viscoelastic properties: Synvisc has viscoelastic properties that are more similar to those of the synovial fluid of young and healthy adults. This positively impacts the efficacy of the product’s lubrication and shock-absorption.
• Clinical outcomes: Researchers examined the differences in clinical and cost outcomes among different viscosupplements and found that Synvisc has a reduced effect in respect to delaying knee replacement surgery when compared to other products, including Orthovisc.
• Hyaluronan sources: While Synvisc is made from rooster and chicken combs, the hyaluronic acid used in Orthovisc is derived from bacterial cells. A study by Petrella et al. found evidence suggesting that products with non-avian-derived hyaluronic acid have a lower risk of causing side effects when compared to products with hyaluronic acid derived from avian sources.
• Adverse event profile: Synvisc is associated with greater incidences of acute local reactions, an occurrence that is not seen with treatment using other viscosupplements, including Orthovisc. These reactions seem to increase in frequency with repeated treatments. The incidence of acute local reactions with Synvisc treatment may be attributed to the product’s manufacturing process, which involves using chemical divinyl sulfone and formaldehyde to crosslink the native hyaluronan. These chemicals may provoke an immunological tissue reaction, leading to pseudosepsis.
Hyaluronic acid viscosupplement injections are a safe and efficacious way to help patients treat and manage their knee osteoarthritis symptoms in the long term. While Synvisc and Orthovisc have great results, there are considerable differences regarding their respective adverse event profiles, product composition, and clinical outcomes.
Patients should always consult a knowledgeable medical practitioner when deciding which of these products is the right one for them.