Knee injections are a common non-surgical intervention used to treat joint pain and stiffness, primarily targeting conditions like osteoarthritis or acute injuries. These procedures involve delivering medication or other therapeutic substances directly into the knee joint space (intra-articularly) for localized relief. The goal is to reduce inflammation, temporarily manage pain, and improve the overall function of the knee. Several types of injections are available, each with a distinct mechanism of action and intended outcome.
Anti-Inflammatory Options: Corticosteroids
Corticosteroid injections, often called “steroid shots,” are a long-standing and widely used treatment for rapid relief from knee pain. They deliver a powerful anti-inflammatory medication directly into the joint capsule, suppressing the inflammatory cascade. This action reduces the production of pro-inflammatory substances, decreasing swelling and lessening the sensitization of nerve endings, which quickly reduces pain.
Relief typically begins within a few days and can last from several weeks to a few months. A local anesthetic, such as lidocaine, is often mixed with the steroid to provide immediate, short-lived pain relief.
Patients may experience a temporary increase in pain, known as a “steroid flare,” in the first 24 to 48 hours after the shot. This discomfort is usually managed with rest and ice. Corticosteroid injections are most appropriate for managing acute flares of arthritis or bursitis rather than serving as a long-term solution.
Viscosupplementation: Hyaluronic Acid
Viscosupplementation involves injecting hyaluronic acid (HA), a gel-like substance, into the knee joint. This treatment is primarily aimed at patients with mild to moderate osteoarthritis. HA is a natural component of synovial fluid, acting as a lubricant and shock absorber.
In an arthritic knee, natural HA degrades, reducing joint protection. The injected HA supplements this diminished fluid, improving lubrication and cushioning the joint surfaces. Therapeutic effects can last up to six months, potentially by stimulating the joint to produce its own HA.
The full benefit of HA injections is slower than steroids, sometimes taking several weeks after the final injection in a series. Depending on the product, HA is often administered as a series of one to five shots, typically spaced one week apart. Patients should avoid strenuous activity for a couple of days following the procedure.
Biologic Treatments: PRP and Stem Cells
A newer category of treatments, known as orthobiologics, uses the body’s own materials to promote healing and tissue repair. Platelet-Rich Plasma (PRP) therapy begins by drawing the patient’s blood and placing it in a centrifuge to concentrate the platelets. This creates a plasma solution with 2 to 8 times the normal platelet count.
Platelets contain hundreds of proteins called growth factors that are released upon injection into the knee, stimulating reparative cells and enhancing the body’s natural healing process. PRP is injected to promote tissue healing and reduce pain in conditions like osteoarthritis or chronic tendon injuries. The benefits are gradual, taking several weeks or months to become fully noticeable.
Stem cell treatments involve harvesting the patient’s own cells, typically from bone marrow or fat tissue. These cells are then injected into the knee with the theoretical goal of regenerating damaged cartilage or tissue.
Both PRP and stem cell therapies are often considered investigational due to a lack of extensive long-term evidence. Consequently, patients seeking these treatments should anticipate paying out-of-pocket, as they are frequently classified as experimental and are not covered by most standard health insurance providers.
The Injection Process and What to Expect
The procedure for receiving a knee injection follows a consistent protocol to maximize safety and efficacy. Patients may be instructed to temporarily stop taking certain medications, such as blood thinners or some anti-inflammatory drugs, to minimize the risk of bleeding. The injection site is thoroughly cleaned with an antiseptic solution to prevent infection.
To ensure precise delivery into the joint space, the practitioner often uses imaging guidance, such as ultrasound or fluoroscopy. These technologies allow the doctor to visualize the joint and confirm accurate needle placement.
Post-care instructions typically include resting the knee for at least 24 hours and avoiding strenuous activities for up to 48 hours. Applying ice to the injection site can help manage any mild, temporary discomfort or swelling.