Biceps Tendon Sheath Injection

Excerpt

Ultrasound (US) is well suited for use in clinical practice given its affordability, portability, and lack of radiation exposure for image acquisition. These features allow clinicians from almost any specialty the ability to perform image-guided evaluations and interventions. Radiologists are uniquely suited to perform these types of evaluations and procedures given their extensive training, knowledge of human anatomy, and understanding of varied anatomical appearances on multiple imaging modalities.

Part of a radiologist’s training comprises an understanding of medical physics, including how medical images are obtained. In ultrasound, the sonographer or physician utilizes a transducer to interrogate the area of interest. Within the transducer are piezoelectric crystals that vibrate when exposed to an alternating current. These vibrations generate sound waves transmitted into the patient’s soft tissues via a layer of ultrasound gel. The sound waves then interact with the tissue and are ultimately reflected back to the transducer. Once the sound waves return to the transducer, they are converted back into an electric current. The computer then calculates the time interval between when the sound wave was initially generated and when it was received back at the transducer to determine the location (depth) of the tissue, which reflected the sound wave.

When planning a procedure, one must consider the type of transducer which will yield the highest quality images. There are a variety of transducers that can be used with varied frequency and shape. In general, higher frequency transducers are utilized for imaging more superficial structures as they offer better resolution. However, the higher frequency sound wave is more easily attenuated and has decreased ability to penetrate tissue, limiting their use in the evaluation of deeper structures. For deeper structures or larger patients, one might choose a lower frequency or curved transducer. When imaging small body parts, such as a finger, a small transducer (hockey stick) may help.

Image guidance for procedures includes the use of ultrasound, fluoroscopy, computed tomography (CT), or in some cases, MRI. In general, ultrasound is particularly helpful in the guidance of soft tissue procedures such as therapeutic tendon sheath injection, soft tissue biopsy, as well as cyst or abscess aspiration/drainage. Ultrasound, CT, and fluoroscopy guidance can be used for both joint aspiration and therapeutic injection. The chosen modality may depend on availability, user expertise, the body part to be treated, and patient body habitus. Advantages to US include lack of ionizing radiation and direct real-time visualization of the needle and surrounding soft tissues during the procedure. During fluoroscopic guidance, the needle is intermittently imaged, and its position is judged only in relation to the associated osseous structures. The involved soft tissue structures must be inferred by knowledge of anatomy. Also, fluoroscopy often requires a contrast agent to verify needle placement as opposed to US, which allows for direct visualization of the needle position. CT is useful for biopsy of osseous structures or therapeutic injection of deep anatomic structures, which can be difficult to visualize with US or palpate on physical examination.