An arthrogram is a specialized medical imaging test that provides a detailed view of the soft tissues inside a joint space. This procedure involves the direct injection of a contrast agent, often called a dye, into the joint capsule. The contrast material coats and fills the structures within the joint, illuminating areas difficult to see on standard images. The injection is immediately followed by a conventional imaging technique, such as X-ray, Computed Tomography (CT), or Magnetic Resonance Imaging (MRI). By combining the contrast with these modalities, the arthrogram significantly enhances the visualization of internal anatomy, including the ligaments, cartilage, tendons, and the joint capsule itself.
Common Uses and Target Joints
A physician typically orders an arthrogram when a patient has persistent, unexplained joint pain or loss of function not fully diagnosed by standard X-rays or non-contrast MRI scans. The enhanced detail is particularly useful for evaluating subtle soft tissue tears, such as partial-thickness tendon tears or labral tears in the hip and shoulder. This technique also helps assess the integrity of the joint capsule and detects loose fragments of bone or cartilage, sometimes called loose bodies, that may be causing mechanical issues.
The procedure is most commonly used to examine larger, complex joints containing significant soft tissue. Frequent targets include the shoulder and hip joints, often to investigate issues like rotator cuff tears or labral damage. Other joints that benefit from this detailed imaging include the knee, examined for meniscal or ligament problems, as well as smaller joints like the wrist, ankle, and elbow.
Preparing for an Arthrogram
Patients must discuss all medications with their physician and the radiologist before the appointment. Blood-thinning drugs, such as anticoagulants or over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs), may need to be temporarily paused for a specific period to minimize the risk of bleeding at the injection site. It is also important to communicate any known allergies to iodine, contrast material, or local anesthetics used during the procedure.
Patients are generally advised to avoid heavy meals immediately prior to the injection, though a full fast is often not required. If the procedure involves a weight-bearing joint (like the hip or knee) or if a sedative is administered, patients must arrange for a responsible adult to drive them home. Additionally, patients should inform the medical team of any recent or current infections, as an active joint infection is a reason to delay the arthrogram due to the risk of spreading bacteria.
The Arthrogram Procedure Step-by-Step
The arthrogram begins with the patient positioned comfortably on an examination table. A radiologist or trained physician cleans the skin over the joint with a sterile, antiseptic solution and places sterile drapes around the area to prevent infection. Next, a local anesthetic, such as lidocaine, is injected through a small needle to numb the skin and deeper tissues leading into the joint space.
To ensure precise delivery into the joint cavity, the physician uses real-time imaging guidance. This guidance is typically fluoroscopy (a live X-ray video) or sometimes ultrasound. A thin needle is advanced toward the joint, and the imaging guidance allows the physician to confirm correct placement before the contrast is introduced. A small amount of contrast is often injected first, and the spread of the dye verifies the needle tip is within the joint capsule.
Once the needle position is confirmed, the main volume of the contrast agent is slowly injected into the joint space. MRI arthrograms typically use a diluted gadolinium solution, while CT arthrograms use an iodine-based contrast. The patient may feel a temporary sensation of fullness or pressure as the fluid enters. Sometimes, a small amount of joint fluid is first aspirated for analysis or to make room for the contrast.
After the injection, the needle is removed. The patient is usually asked to gently move the joint to ensure the contrast thoroughly coats all internal structures. This movement is crucial for the dye to seep into small tears or irregularities, making them visible on subsequent scans. Following this preparation, the patient is immediately transferred to the CT or MRI scanner for the final diagnostic images, as the contrast agent begins to be absorbed by the body relatively quickly.
After the Procedure and Safety Considerations
After imaging, the injection site is covered with a small bandage, and patients are advised to rest the joint for the remainder of the day. Mild swelling, soreness, or a feeling of fullness in the joint is common for 12 to 24 hours. Patients may also feel an audible clicking or cracking sensation as the contrast fluid moves. Discomfort can be managed by applying ice intermittently and taking over-the-counter pain relievers like acetaminophen.
Patients should avoid strenuous activity or heavy lifting with the affected limb for about a day to allow the injection site to heal and to prevent irritation of the joint. While arthrograms are generally safe, risks include bleeding, bruising, or a mild allergic reaction to the contrast dye. The most serious, though rare, complication is a joint infection, which is estimated to occur in about 1 out of 40,000 procedures.
Patients should contact their doctor immediately if they develop signs of a potential complication:
- Fever
- Excessive redness or increasing warmth
- Significant pain that worsens instead of improving after the first day
- Persistent or increasing swelling or any discharge from the injection site