The gel injection for knees is called viscosupplementation, and the substance injected is hyaluronic acid (also called sodium hyaluronate or hyaluronan). You may hear it referred to as a “gel shot,” “rooster comb injection,” or simply by one of its brand names, with Synvisc-One, Euflexxa, and Monovisc being among the most widely recognized. There are currently 12 FDA-approved viscosupplementation products in the United States, all designed to treat knee osteoarthritis pain.
How Hyaluronic Acid Works in the Knee
Your knee joint naturally contains a thick fluid called synovial fluid, and hyaluronic acid is a key component of it. In a healthy knee, hyaluronic acid molecules link together to form a viscous solution that acts as both a lubricant and a shock absorber. When osteoarthritis breaks down cartilage, the concentration and quality of natural hyaluronic acid in the joint drops. The joint loses its cushioning, and bones start grinding more directly against each other.
Injecting hyaluronic acid back into the joint does more than just add lubrication. It triggers the joint’s own cells to produce more hyaluronic acid on their own. It also reduces the activity of inflammatory enzymes and proteins that drive osteoarthritis progression, lowers nerve sensitivity in the joint (which directly reduces pain), and stimulates cartilage cells to produce more collagen. So the injection works both mechanically, by restoring cushion, and biologically, by calming inflammation and supporting cartilage repair.
FDA-Approved Brand Names
Not all gel injections are the same. They differ in how many shots you need and in their molecular weight. Here are the 12 FDA-approved options:
Single-injection brands:
- Synvisc-One (hylan G-F 20)
- Monovisc (hyaluronan)
- Durolane (hyaluronic acid)
- Gel-One (hyaluronate)
Two-injection brands:
- Hymovis (hyaluronan), given as 2 weekly injections
Three-injection brands:
- Euflexxa (sodium hyaluronate)
- Gelsyn-3
- Orthovisc (hyaluronan)
- Supartz FX
- Synvisc (hylan G-F 20)
Five-injection brands:
- Genvisc 850 (sodium hyaluronate)
- Hyalgan (sodium hyaluronate), which can also be given as 3 injections
Your doctor will typically choose based on your insurance coverage, how many office visits you can manage, and their own clinical experience with a particular product.
Who Is a Good Candidate
Gel injections are considered appropriate for adults with mild to moderate knee osteoarthritis confirmed by X-ray. A panel of specialists rated hyaluronic acid as an appropriate treatment for both mild and moderate osteoarthritis regardless of whether patients had already tried other treatments. For severe osteoarthritis, with large bone spurs and significant joint space loss, the evidence is less clear and the appropriateness rating drops to “uncertain.”
In practical terms, the best candidates are people whose knee pain interferes with daily activities like walking or standing for long periods, who still have some cartilage left in the joint, and who haven’t gotten enough relief from other options. If your knee is bone-on-bone with major structural damage, your doctor may recommend a knee replacement instead.
What to Expect: Timeline and Results
Gel shots don’t provide instant relief. It generally takes 4 to 6 weeks before you feel the full benefit. This is different from cortisone injections, which often reduce pain within days. The tradeoff is duration: once hyaluronic acid kicks in, relief typically lasts about six months before symptoms start returning. At that point, you can receive another round of injections.
It’s worth knowing that gel shots don’t work for everyone. Some people experience significant pain relief and improved mobility, while others notice little difference. If you do respond well to a first round, that’s a good sign that repeat treatments will also help.
Side Effects
The most common side effects are mild and localized: temporary pain, swelling, or warmth at the injection site. Some people experience what’s called a “gel flare,” where the knee swells and becomes painful in the hours or days after the injection. This reaction looks alarming but typically resolves on its own with ice and rest. Serious complications like joint infection are rare.
Insurance Coverage Requirements
Most insurance plans, including Medicare, cover viscosupplementation, but with conditions. Medicare considers the treatment reasonable and necessary only when all of the following are documented: your knee pain interferes with daily activities like walking, X-rays confirm osteoarthritis, you’ve tried and failed at least 3 months of conservative treatment (physical therapy, exercise, weight management, over-the-counter pain relievers), and you’ve either tried corticosteroid injections without success or have a reason you can’t receive them.
For repeat treatments, insurers typically require that at least 6 months have passed since your last round and that you experienced measurable improvement from the previous series. If your doctor recommends gel injections, expect a prior authorization process where your insurance reviews your treatment history before approving coverage. Out-of-pocket costs without insurance can range from several hundred to over a thousand dollars per treatment series, depending on the brand and number of injections required.