Gel injections, or viscosupplementation, offer a treatment option for individuals experiencing pain from knee osteoarthritis (OA). This procedure involves injecting a gel-like substance directly into the knee joint to supplement the natural fluid degraded by the condition. Osteoarthritis causes the protective cartilage to break down, leading to pain, stiffness, and reduced mobility. The goal is to restore some of the joint’s natural lubrication and cushioning properties to help the bones glide more smoothly. This approach is considered when conservative treatments, such as oral pain relievers and physical therapy, have not provided sufficient relief.
The Role of Hyaluronic Acid Injections
The injected substance is a form of hyaluronic acid (HA), a molecule that occurs naturally in the body and is a major component of healthy synovial fluid. In a healthy joint, this fluid acts as a shock absorber and lubricant, enabling smooth movement and protecting the articular cartilage. However, in a knee affected by osteoarthritis, the concentration and quality of the naturally occurring HA decrease significantly.
The injection supplements the depleted natural HA, restoring the viscoelastic properties of the synovial fluid. This process provides a mechanical benefit by improving joint lubrication, which reduces friction and pain. HA may also exert anti-inflammatory effects by reducing pro-inflammatory substances within the joint. This treatment is typically used after initial measures like nonsteroidal anti-inflammatory drugs (NSAIDs) or corticosteroid injections have failed, but before considering total knee replacement.
Comparing Available Viscosupplementation Treatments
The question of which gel injection is “best” does not have a single answer, as products differ primarily in their chemical structure and dosing schedules. These differences are categorized by the HA’s molecular weight, its source, and the number of injections required. HA preparations are classified by molecular weight (MW) into low, medium, high, and ultra-high categories, which affects how viscous, or thick, the gel is.
Some evidence suggests that higher-molecular-weight HA formulations may provide a greater reduction in pain compared to lower-molecular-weight products, particularly in the short to mid-term (up to six months). These thicker preparations better mimic the viscosity of healthy joint fluid and may possess stronger shock absorption. However, the thicker nature of high MW products can be associated with a slightly higher incidence of injection-site side effects, such as temporary swelling or pain.
The most notable practical difference for patients is the dosing schedule, which can range from a single injection to a series of three or five injections. Single-injection products offer considerable convenience, requiring only one office visit to complete the full treatment course. Multiple-injection series, typically given once a week, spread the total dose over a longer period.
Studies comparing single-dose versus multi-dose regimens have not consistently shown one to be universally superior. The choice often comes down to patient preference for convenience versus a more gradual therapeutic effect. Another distinction is the source of the HA, which can be derived from avian sources or produced non-avianly through bacterial fermentation. Patients with known allergies to poultry or eggs should avoid avian-derived products.
What to Expect During the Injection Process
The injection process is a quick, in-office procedure that begins with preparation of the site. The healthcare provider cleans and sterilizes the area around the knee to minimize the risk of infection. A local anesthetic may be injected first to numb the skin and the joint area, reducing discomfort during the procedure.
The provider may use imaging guidance, such as ultrasound or fluoroscopy, to ensure the needle is positioned accurately within the joint space. If there is excess fluid buildup in the knee, aspiration may be performed to drain the fluid before the HA is injected. The HA product is then slowly injected into the joint, the needle is removed, and a small bandage is applied.
Following the injection, patients are generally able to go home immediately. It is recommended to avoid strenuous activities like jogging, heavy lifting, or prolonged standing for the first 48 hours to allow the joint to settle. Patients may use ice packs to help with any minor post-injection soreness or swelling.
Potential Side Effects and Contraindications
Potential Side Effects
Most people tolerate viscosupplementation well, with the most common reactions being mild and temporary. These mild side effects include local pain, warmth, slight swelling, or redness at the injection site. These symptoms are usually short-lived and can often be managed with ice application and rest.
A less common but more severe reaction, occurring in about 1% of patients, is an injection flare or pseudo-sepsis. This involves significant pain, swelling, and warmth in the knee, mimicking a joint infection, though it is not caused by bacteria. True joint infection, known as septic arthritis, is an extremely rare but serious complication that requires immediate medical attention.
Contraindications
Certain conditions serve as contraindications, meaning the injection should not be administered. Patients with a known hypersensitivity or allergy to hyaluronic acid or any components of the formulation should not receive the treatment. The injection should also be avoided in patients with an active skin infection near the injection site.