Ultrasoundguided Injections

Certain articular compartments are amenable to ultrasound-guided anesthetic injections. This technique is especially useful in satellite imaging centers or clinical settings where fluoroscopy units are unavailable. It is also cost effective because iodinated contrast material is not needed. In addition, the lack of ionizing radiation with sonographic guidance is an added benefit.

FIGURE 13 Patient positioning for elbow injection.

Sonographically guided injections of the knee and hip have been described (13). An effusion within these joints facilitates verification of intra-articular needle position by providing a sonographic window through which the hyperechoic needle tip is visualized. Small amounts of air can also be injected to demonstrate hyperechoic bubbles within the joint fluid. This guidance technique is more difficult to perform in the absence of a joint effusion.

Sonographically guided injections of the knee are performed by localizing fluid (Fig. 15A) within the suprapatellar synovial bursa typically with a transverse orientation (Fig. 15B) of a linear, high-frequency transducer, that is, 13 MHz. The needle is then placed into the joint fluid entering the skin superolateral to the patella (Fig. 15C). If no fluid is present within the knee, the needle is placed into the lateral patellofemoral compartment by palpation alone. Intra-articular placement can then be assessed by injecting small amounts of air through a syringe attached to the needle. The echogenic bubbles of air should then be visualized by sonographic interrogation of the suprapatellar bursa (Fig. 16).

FIGURE 14 Lateral fluoroscopic image during elbow injection.

FIGURE 15 (A) Sonographic visualization of suprapatellar fluid with echogenic needle shaft (arrow) and femoral shaft. (B) Transducer positioning for knee injection. (C) Needle/transducer positioning for knee injection. Abbreviations: Fl, suprapatellar fluid; Fs, femoral shaft. Source: Courtesy of Henning Bliddal M.D., The Parker Institute, H:S Frederiksberg Hospital, Copenhagen, Denmark.

FIGURE 15 (A) Sonographic visualization of suprapatellar fluid with echogenic needle shaft (arrow) and femoral shaft. (B) Transducer positioning for knee injection. (C) Needle/transducer positioning for knee injection. Abbreviations: Fl, suprapatellar fluid; Fs, femoral shaft. Source: Courtesy of Henning Bliddal M.D., The Parker Institute, H:S Frederiksberg Hospital, Copenhagen, Denmark.

FIGURE 16 Sonographic image demonstrating layering air bubbles (small arrows), needle shaft (large arrow) and femoral shaft, and joint fluid. Abbreviations: Fl, joint fluid; Fs, femoral shaft. Source: Courtesy of Henning Bliddal M.D., The Parker Institute, H:S Frederiksberg Hospital, Copenhagen, Denmark.

FIGURE 16 Sonographic image demonstrating layering air bubbles (small arrows), needle shaft (large arrow) and femoral shaft, and joint fluid. Abbreviations: Fl, joint fluid; Fs, femoral shaft. Source: Courtesy of Henning Bliddal M.D., The Parker Institute, H:S Frederiksberg Hospital, Copenhagen, Denmark.

FIGURE 17 Transducer positioning for hip injection. Source: Courtesy of Henning Bliddal M.D., The Parker Institute, H:S Frederiksberg Hospital, Copenhagen, Denmark.

Hip injections are performed with the patient supine and with a lower frequency linear transducer such as 8 MHz, which is needed for deeper penetration of the thicker soft tissues overlying the hip. The transducer is placed parallel to the femoral neck (Fig. 17) and the needle is inserted 8 to 10 cm below the inguinal ligament to enter the anteroinferior joint capsule just below the femoral head (Fig. 18A and B). As with knee injections, this technique is facilitated by a joint effusion but can be performed successfully without an effusion. Injection of a small amount of air verifies the intra-articular needle position (Fig. 19A and B). A distinct advantage of sonography during hip injections is the real-time visualization of the femoral artery and vein, utilizing color Doppler evaluation, thus increasing safety and reducing the risk of vascular complications.

FIGURE 18 (A) Needle/transducer positioning for hip injection. (B) Needle trajectory relative to sonographically visualized femoral neck and femoral head. Source: Courtesy of Henning Bliddal M.D., The Parker Institute, H:S Frederiksberg Hospital, Copenhagen, Denmark.
FIGURE 19 (A) Layering echogenic air bubbles within hip joint capsule (arrows). (B) Diagram. Source: Courtesy of Henning Bliddal M.D., The Parker Institute, H:S Frederiksberg Hospital, Copenhagen, Denmark.

The choice of imaging guidance should be based on personal preference and operator experience.

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