Intramuscular (IM) injections deliver medications directly into muscle tissue for rapid absorption. While generally effective and well-tolerated, administering these injections requires precision to avoid complications. Proper technique, including careful site selection and adherence to established procedures, is important to ensure both medication effectiveness and patient safety.
Why Sciatic Nerve Avoidance Matters
The sciatic nerve is the longest and widest nerve in the human body, originating from the lower spine (L4 to S3 nerve roots) and extending down the back of each leg into the foot. It controls motor function and provides sensation to the legs. The sciatic nerve passes through the gluteal muscles, making it susceptible to injury during injections.
Accidental injury to the sciatic nerve during an injection can lead to severe and long-lasting consequences. Patients may experience immediate, sharp, or electric shock-like pain radiating down the leg. This can progress to numbness, tingling, muscle weakness, or even partial or permanent paralysis, particularly affecting foot movement (known as foot drop). Such injuries are preventable, emphasizing the need for careful injection practices.
Identifying Safe Injection Sites
Selecting the correct anatomical site is important to avoid sciatic nerve injury during intramuscular injections. The ventrogluteal site is the safest and preferred location for adults and children due to its substantial muscle thickness and distance from major nerves and blood vessels, including the sciatic nerve. To locate this site, position the patient on their side with the knee and hip flexed to relax the muscle. Place the palm of the hand opposite the injection site on the greater trochanter of the hip, with the thumb pointing towards the groin. Extend the index finger to the anterior superior iliac spine and spread the middle finger along the iliac crest, forming a V-shape; the injection is administered in the center of this V.
The dorsogluteal site, located in the upper outer quadrant of the buttock, was once a common injection area but is now discouraged due to its proximity to the sciatic nerve and higher risk of nerve damage.
Other safe intramuscular injection sites include the vastus lateralis and the deltoid. The vastus lateralis muscle, located on the outer thigh, is a preferred site for infants and children and can accommodate up to 5 mL in adults. To landmark, locate the area between one hand’s breadth below the greater trochanter and one hand’s breadth above the knee, injecting into the middle third of this region. The deltoid muscle in the upper arm is suitable for smaller volumes, up to 2 mL, and is located about 2.5 to 5 cm (1 to 2 inches) below the acromion process, the bony prominence of the shoulder.
Proper Injection Techniques
Beyond selecting a safe site, proper technique ensures medication delivery into the muscle while minimizing harm. Patient positioning is important, as relaxed muscles allow for easier and safer injection. For instance, the ventrogluteal site benefits from the patient lying on their side with the hip and knee bent.
Accurate landmarking is important for each site to ensure the needle enters the intended muscle mass and avoids underlying structures. Once the site is identified and cleaned with an alcohol swab, allow the skin to dry completely to prevent stinging. The needle should be inserted with a quick, dart-like motion at a 90-degree angle to the skin.
Aspiration, which involves pulling back on the plunger for about 5 seconds before injecting, is a common practice to check for blood return, indicating the needle has entered a blood vessel. If blood appears, the needle should be withdrawn, discarded, and the injection re-prepared and administered at a new site. Aspiration is not performed for immunizations, as major blood vessels are avoided in recommended vaccine injection sites. The Z-track method, where the skin is pulled laterally before injection and released after, helps seal the medication in the muscle and prevents leakage into the subcutaneous tissue. After injection, apply gentle pressure with gauze to the site without rubbing.
Recognizing Nerve Contact
Even with careful technique, it is important to recognize signs of nerve contact. If the needle touches a nerve, the patient may experience immediate, sharp, shooting pain, often described as an electric shock sensation, radiating down the limb. Other signs include sudden numbness or tingling in the affected area.
If any of these symptoms occur during an injection, the needle should be withdrawn immediately. Persistent or worsening symptoms, such as ongoing pain, numbness, or muscle weakness, warrant prompt medical attention to assess potential nerve damage and determine appropriate treatment, which may include physical therapy or pain management.