Knee injections are a widely used non-surgical approach for managing pain and inflammation within the joint, most commonly associated with osteoarthritis or bursitis. These procedures involve delivering a therapeutic substance directly into the knee joint space (intra-articularly) to provide localized relief. A licensed medical professional, such as an orthopedic surgeon, rheumatologist, or pain management specialist, performs the injection in an outpatient setting. The goal is to reduce discomfort, improve mobility, and potentially delay the need for more invasive treatments like surgery.
Common Types of Knee Injections
The two most frequently administered substances are corticosteroids and hyaluronic acid, each serving a distinct purpose. Corticosteroid injections, often called cortisone shots, are anti-inflammatory medications. They work by suppressing the localized immune response and inflammation that cause pain and swelling in the joint. Pain relief is typically short-term, beginning within a few days to a week and lasting for a few weeks to several months.
Viscosupplementation involves injecting hyaluronic acid (HA), a complex sugar molecule naturally found in healthy joint fluid, into the joint space. In a knee affected by osteoarthritis, natural HA can become depleted, reducing its ability to act as a lubricant and shock absorber. Injecting synthetic HA restores the fluid’s properties, improving the joint’s gliding motion. This treatment often involves a series of three to five weekly injections, and the therapeutic effect may take several weeks after the final shot to become noticeable.
Other options, often termed regenerative therapies, include Platelet-Rich Plasma (PRP) and stem cell injections. PRP is created by concentrating a patient’s own platelets and growth factors from a blood sample, which is then injected to stimulate a healing response. Stem cell treatments, typically using cells harvested from the patient’s bone marrow or fat, are considered for more severe joint damage. These newer treatments are generally less standardized and more costly than corticosteroids or hyaluronic acid.
Preparing for the Procedure
Preparation for a knee injection begins with a thorough medical consultation where the physician reviews the patient’s history, including any known allergies. Patients must disclose all medications, particularly blood thinners (such as aspirin or warfarin) and non-steroidal anti-inflammatory drugs (NSAIDs). The medical team will advise if and for how long these medications must be temporarily stopped to minimize the risk of bleeding at the injection site, a decision carefully balanced against the patient’s risk of blood clots.
For corticosteroid injections, patients with diabetes should be aware that the steroid can temporarily raise blood sugar levels, requiring a monitoring and adjustment plan. On the day of the procedure, wearing loose-fitting clothing that allows easy access to the knee is recommended. Patients are often advised to arrange for a ride home, especially if a local anesthetic is used, as temporary numbness or weakness could affect driving ability. Before the procedure, the patient provides informed consent after discussing potential risks like infection or nerve damage.
The Injection Process
The procedure begins with the patient positioned appropriately, often lying supine with the knee slightly flexed, to allow easy access to the joint space. The medical professional then uses an aseptic technique to rigorously clean the injection area with an antiseptic solution to prevent infection. A local anesthetic, such as lidocaine, is typically injected into the skin and underlying tissues to numb the area before the larger needle is inserted for the main injection.
Modern knee injections routinely use imaging guidance, primarily ultrasound or fluoroscopy (a type of real-time X-ray). This guidance allows the clinician to visualize the needle’s trajectory and confirm its precise placement within the joint capsule, which dramatically increases accuracy compared to a “blind” injection. Once the needle is positioned correctly, the clinician may first aspirate, or withdraw, any excess fluid or swelling from the joint, especially if a large effusion is present.
Following aspiration, the therapeutic substance—whether a corticosteroid, hyaluronic acid, or a regenerative therapy—is slowly injected into the joint. A test dose of anesthetic may be used to confirm proper placement before the full dose of medication is delivered. The injection should meet minimal resistance, confirming the needle is freely positioned within the joint space. The needle is then quickly removed, and a small bandage is applied. The entire injection process is usually brief, often taking less than 15 minutes.
Recovery and Post-Procedure Instructions
Immediately following the injection, patients are asked to rest the knee and avoid strenuous activity for the next 24 to 48 hours. This restriction includes avoiding high-impact activities, heavy lifting, and prolonged standing, allowing the injected substance to settle without excessive joint stress.
Patients may experience mild pain, swelling, or soreness at the injection site for a couple of days. Applying ice for short intervals can help manage this localized discomfort, but heat should be avoided for the first 48 hours. A temporary worsening of joint pain, known as a “steroid flare,” can occur within the first 48 hours after a corticosteroid injection. This is a self-limiting reaction caused by the body’s response to the steroid crystals and typically resolves within a few days.
The timeline for pain relief varies depending on the substance injected. Corticosteroids typically start providing relief within two to five days, though the initial anesthetic may wear off in a few hours. Hyaluronic acid’s effects are often delayed, sometimes taking several weeks after a series of injections to feel the full benefit. Patients must monitor the injection site for warning signs of a serious complication, such as infection. Symptoms like severe, increasing pain, spreading redness, warmth, discharge, or a fever above 100.4°F require immediate medical attention.