Gel injections, formally known as viscosupplementation, are a treatment option for individuals experiencing knee pain caused by osteoarthritis. This procedure involves injecting a gel-like substance directly into the knee joint to help restore the natural cushioning and lubricating properties diminished by the disease. This therapy aims to reduce pain and improve joint function for patients who have not found sufficient relief from initial treatments like pain relievers and physical therapy. This article evaluates the scientific basis of these injections, the procedure involved, and current evidence regarding their effectiveness.
What Gel Injections Are and How They Work
The substance used in these knee injections is hyaluronic acid, a polysaccharide naturally present in the body. Hyaluronic acid is a key component of healthy synovial fluid, the viscous liquid that fills the joint capsule. In a healthy knee, this fluid acts as both a lubricant to reduce friction and a shock absorber to protect the joint during movement.
In a knee affected by osteoarthritis, the concentration and quality of hyaluronic acid decrease, compromising the synovial fluid’s ability to protect the joint. Viscosupplementation restores the fluid’s viscoelastic properties by supplementing it with exogenous hyaluronic acid. By enhancing the fluid’s thickness and elasticity, the injected “gel” reduces mechanical friction between the bones, a major source of pain. The substance also appears to have biochemical effects, downregulating pro-inflammatory factors and enzymes associated with the disease, which contributes to decreased inflammation and improved mobility.
The Viscosupplementation Procedure and Safety Profile
The viscosupplementation procedure involves several steps. Before the injection, the physician cleanses and sterilizes the skin around the knee to minimize the risk of infection. A local anesthetic is often applied to numb the area, making the process more comfortable.
The physician may use image guidance, such as ultrasound or fluoroscopy (a type of X-ray), to ensure accurate needle placement into the joint space. If there is excess fluid or swelling, aspiration may be performed to draw out the fluid before the hyaluronic acid is injected. Depending on the specific product used, the patient may receive a single injection or a series of three to five injections spaced about a week apart.
Following the procedure, patients are usually advised to avoid strenuous activities like jogging or heavy lifting for the first 48 hours. The safety profile of viscosupplementation is favorable, with most adverse events being localized, mild, and temporary. Common side effects include mild pain, swelling, or warmth at the injection site. A more severe, though rare, adverse event is an “injection flare,” which involves significant temporary swelling and pain in the joint.
Measuring the Effectiveness of Gel Injections
The effectiveness of gel injections is often measured by patient-reported outcomes, such as pain reduction scales and improvements in daily functional activities. Scientific studies suggest that the onset of pain relief from viscosupplementation is slower than that of corticosteroid injections, often taking several weeks to reach its full effect. Once relief begins, it tends to be more sustained than with steroid shots, lasting three to six months, and sometimes longer.
Results from the treatment are variable, meaning not all patients respond equally to the injections. Viscosupplementation is considered a second-line treatment, recommended for individuals with mild to moderate knee osteoarthritis who have failed to find adequate relief from conservative methods like physical therapy and nonsteroidal anti-inflammatory drugs. It is also considered for patients who need to avoid systemic medications or who are not yet candidates for total knee replacement surgery.
The scientific consensus on the benefit of these injections has been mixed, leading to differing recommendations among major medical organizations. Some guidelines, such as those from the American Academy of Orthopaedic Surgeons, have expressed reservations due to inconsistent results in clinical trials. Other expert groups find hyaluronic acid to be an effective treatment with a favorable benefit-to-risk ratio, especially when compared to placebo or other injection types in the medium-term. For many patients, viscosupplementation offers a meaningful, non-surgical option that bridges the gap between early-stage conservative management and more invasive procedures.