Osteoarthritis (OA) is a common condition where the protective cartilage in the knee joint wears down, resulting in pain, stiffness, and reduced mobility. The treatment commonly known as “gel injections” is a non-surgical option for managing this discomfort. This procedure involves injecting a specialized substance directly into the knee joint to potentially alleviate symptoms when pain is not controlled by more conservative therapies.
Viscosupplementation: Defining Gel Injections
The treatment referred to as a “gel injection” is medically termed viscosupplementation, designed to address pain from knee osteoarthritis. This therapy involves injecting hyaluronic acid (HA), a gel-like substance, directly into the knee joint cavity. HA is a naturally occurring complex sugar molecule and a primary component of healthy synovial fluid, which lubricates and cushions the joint. The goal of viscosupplementation is to supplement the depleted synovial fluid found in an osteoarthritic joint. These prescription-only injections are regulated by the U.S. Food and Drug Administration (FDA) specifically for treating knee OA.
How Hyaluronic Acid Works in the Knee Joint
In a healthy knee, synovial fluid contains high concentrations of HA, giving the fluid its viscoelastic properties. This unique quality allows the fluid to function as a lubricant and shock absorber, reducing friction and protecting the articular cartilage during movement. When osteoarthritis develops, the quality and concentration of natural HA decrease, making the synovial fluid less effective at cushioning the joint.
The injected HA aims to restore the joint’s mechanical properties by increasing fluid viscosity. This helps reduce friction and mechanical stress between the cartilage surfaces and underlying bone. HA may also have biological effects, including mild anti-inflammatory properties that inhibit pro-inflammatory substances, potentially reducing pain and stiffness.
Patient Eligibility and Expected Efficacy
Viscosupplementation is typically reserved for patients with mild to moderate knee osteoarthritis. These injections are considered a second-line treatment option, meaning they are recommended after a patient has failed to find adequate relief from conservative treatments. Initial therapies include weight management, physical therapy, and nonsteroidal anti-inflammatory drugs (NSAIDs).
Patients with severe, advanced, or “bone-on-bone” osteoarthritis often see less benefit from the injections, as there is little cartilage remaining for the HA to protect. The injections are also sometimes used as a temporary measure to delay or avoid total knee replacement surgery. Efficacy can vary significantly among individuals, which contributes to the mixed scientific consensus on the treatment’s overall effectiveness.
Onset and Duration of Relief
For positive responders, the onset of pain relief is often delayed compared to corticosteroid injections, which offer rapid but short-lived relief. Patients may not notice symptom reduction until several weeks after the injection, or after completing a series of shots if multiple doses are required. The duration of pain relief typically lasts for several months, with benefits often reported for three to six months before a repeat injection is considered. Viscosupplementation can be comparable to or better than other non-operative treatments for long-term pain relief.
Potential Risks and Post-Injection Care
Like any intra-articular procedure, viscosupplementation carries potential risks, although the most common side effects are temporary and localized. Immediately following the injection, patients frequently experience mild, transient pain, swelling, or stiffness at the injection site. Applying ice to the knee for short intervals can help to manage this immediate discomfort.
A more serious, though rare, complication is an acute inflammatory reaction known as “injection flare” or pseudoseptic arthritis, which causes severe pain and swelling within the joint. The rarest and most serious risk associated with any joint injection is septic arthritis, a joint infection that requires immediate medical attention. Signs of a severe issue include a fever, escalating pain that does not subside after 48 hours, or significant warmth and redness around the injection site.
Post-Injection Care
Post-injection care is important for maximizing the treatment’s success and minimizing irritation. Patients are generally advised to rest the knee and avoid strenuous activity for at least 48 hours after the procedure. This means refraining from jogging, heavy lifting, or high-impact sports. Patients should also keep the injection site clean and dry for a full day and avoid submerging the knee in water for two days.