A “gel injection” into the knee, medically known as viscosupplementation, is a common treatment for the pain associated with knee osteoarthritis. This procedure involves injecting a hyaluronic acid-based fluid directly into the joint space to improve function. Patients are often concerned when their knee pain seems to worsen immediately after the injection. This initial discomfort is a well-recognized, temporary reaction to the procedure and does not mean the treatment has failed. Understanding the reasons for this pain and the treatment mechanism helps manage expectations and recovery.
Causes of Immediate Post-Injection Pain
The acute pain experienced immediately following viscosupplementation is a temporary inflammatory response. The introduction of any foreign material into the joint space can trigger a reaction from the body, even though hyaluronic acid is naturally occurring. This response is often referred to as a post-injection flare or transient synovitis, which is inflammation of the joint lining.
Mechanical irritation from the injection process itself also contributes to the immediate discomfort. The needle passing through the tissues and into the joint capsule can cause minor trauma to the surrounding structures. Furthermore, the injection temporarily increases the volume and pressure inside the joint capsule, stretching the sensitive tissue lining the joint.
This transient increase in pressure and fluid can lead to a sensation of fullness, stiffness, and increased pain. This expected inflammatory reaction is localized and is not a sign of a serious complication in the first 48 hours.
How Viscosupplementation Works
The purpose of a hyaluronic acid injection is to restore the synovial fluid, which acts as the natural lubricant and shock absorber within the joint. In an osteoarthritic knee, this fluid loses its viscosity and elasticity, contributing to pain and stiffness. Hyaluronic acid is a gel-like substance that mimics healthy joint fluid, helping to lubricate the joint surfaces.
The injected gel acts as a cushion, helping joint surfaces move smoothly against each other, reducing friction and absorbing impact forces. Although the injection causes temporary inflammation, it provides a long-term therapeutic effect, including anti-inflammatory properties, after the initial flare subsides. Pain relief is not immediate and often builds up over several weeks as the gel integrates into the joint environment.
Managing Discomfort and the Recovery Timeline
For the temporary soreness after the procedure, several self-care strategies can help manage the discomfort. Resting the knee and avoiding strenuous activity, like jogging, heavy lifting, or standing for long periods, is recommended for the first 48 hours. Applying a cold pack or ice wrapped in a towel to the injection site can help reduce localized swelling and pain.
Over-the-counter pain relievers such as acetaminophen can be used for post-injection soreness. Patients should confirm with their physician whether to use nonsteroidal anti-inflammatory drugs (NSAIDs), as doctors may advise against them. Soreness, warmth, and mild swelling should resolve quickly, typically within one to three days. Adhering to the recovery timeline and limiting weight-bearing activities ensures the best outcome.
Recognizing Serious Signs
While temporary pain is normal, it must be distinguished from serious complications that require immediate medical attention. If pain and swelling significantly worsen after the initial two to three days, or if they are accompanied by systemic symptoms, contact your doctor immediately.
Signs of a possible joint infection, known as septic arthritis, include fever, severe escalating pain, intense warmth, and noticeable redness of the entire joint. A less common but severe reaction is pseudo-sepsis, which mimics an infection with severe pain and swelling but is sterile. These severe acute localized reactions are urgent situations requiring medical evaluation, often through fluid aspiration, to rule out infection and treat the inflammation.