![]() Inclusion of iodinated contrast medium allows fluoroscopic visualization during the injection. The mixture contains iodinated contrast medium, local anesthetic, and saline solution to achieve the correct dilution. TABLE 2: Examples of Medications Used and Volumes (mL) for Arthrographyįor MR arthrography, although a range of dilutions of gadolinium may be used, a 1:200 dilution affords excellent imaging in most cases. If a steep angle cannot be avoided, other methods of improving needle visibility include jiggling the needle and hydrodissection with anesthetic to locate the tip. Beam steering can also be used to improve nedle visibility. 1 ) can also help to produce an angle between the transducer and the needle that is closer to parallel. One strategy to accomplish this is to place the puncture site farther from the probe to achieve a longer but flatter trajectory with respect to the transducer. Planning a skin entry site that allows a shallow needle trajectory maximizes needle visibility: visualization markedly diminishes with angles approaching 40°. An in-plane approach, with the needle positioned parallel to the mid-line of the long axis of the transducer, is generally preferable to the out-of-plane technique so that the needle can be seen throughout the procedure. ![]() Ultrasound guidance has several advantages: patient positioning and needle trajectory are more easily fine-tuned soft-tissue anatomic features are directly visualized and either avoided (nerve, vessel) or targeted (effusion) the needle can be maneuvered in real time instead of intermittently observed and ionizing radiation is avoided. For patients with an allergy to iodinated contrast material, full-strength gadolinium or air may be used, or the injection may be performed under ultrasound guidance. Intraarticular position is confirmed when contrast medium can be injected with little resistance and flows freely into the joint recesses rather than clustering around the needle tip. An osseous backstop should be used whenever possible to ensure correct depth. In addition to adjustment of the needle hub to direct the position of the tip, the tendency of the needle tip to migrate away from its bevel allows the radiologist to steer the needle path to achieve subtle corrections, especially when muscle spasm or tissue planes divert the needle from the target. Centering the beam on the skin entry site avoids parallax and distortion. The fluoroscopic approaches described in this article rely on aligning the fluoroscopic beam with the needle trajectory so the needle appears as a small dot (bull's-eye technique). ![]() TABLE 1: Needle Sizes and Lengths Used for Joint Access Imaging provides an invaluable visual reference, but it is also important to develop a tactile sense of the needle encountering different tissue types and entering the joint. Appropriate needle gauge and length depend on the joint being targeted ( Table 1). The needle is advanced into the joint with either intermittent fluoroscopic guidance or under direct ultrasound visualization. Cutaneous and tract anesthesia are achieved with local anesthetic (1% lidocaine buffered with sodium bicarbonate) and small-gauge needles (25–30 gauge). Sterile technique is used, including mask, sterile gloves, and sterile preparation. For ultrasound-guided injections, preprocedural scanning is used to plan the needle trajectory, identify the target site, and localize adjacent neurovascular structures and tendons to avoid. For fluoroscopy, a radiopaque object is placed on the skin overlying the target to mark an appropriate skin entry site. Careful patient positioning before the procedure facilitates patient comfort and safe and efficient access to the joint.
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