Chapter 21

Joint pain and swelling are common complaints in the acute care setting. Diagnostic arthrocentesis may be required to rule out an infectious process or hemarthrosis. Joint aspiration may also relieve joint pain and allow for infusion of medications when appropriate. Much of the technique and equipment for ultrasound-guided arthrocentesis is the same as for a landmark-based approach. The use of ultrasound can determine the presence of a joint effusion and increase the success rate of arthrocentesis while decreasing complications. Ultrasound may also assist in directing a needle into a joint space even when no effusion exists (ie, for injection of dye to determine joint disruption in trauma or for injection of medications).

Bedside ultrasound-guided arthrocentesis should be used for:

• The patient with nontraumatic joint pain
• Large or painful joint effusions
• The diagnosis of traumatic arthrotomy
• The injection of medications into the joint space

### Linear-Array Probe with a Frequency of 5.0–12.0 MHz

A linear-array probe is best suited for arthrocentesis because of its high resolution and linear configuration. A curvilinear abdominal probe with a 3.0–5.0 MHz frequency can also be used for deeper joints such as the hip or in obese patients. A "hockey stick" or pediatric linear probe may be used for smaller joints.

### Machine Preset

If available, a superficial or bone preset should be utilized on the machine in order to optimize the image obtained.

### Focus

The focus should be adjusted so that it is at the level of the joint of interest. This will help to improve the lateral resolution of the image.

### Depth

The sonographer should initially start off deep and survey the whole joint. The depth should then be reduced so that the area where the needle will be introduced takes up most of the screen.

### Gain or Time-Gain Compensation

The overall gain should be adjusted in order to enhance the brightness of the image as needed. It is often better for the sonographer to increase the far gain of the image only, using time-gain compensation (TGC), in order to improve the quality of the deeper structures. It is important to not use too much gain, which can result in obscuring other important structures within the joint, such as anechoic blood vessels.

### Sterile Precautions

Arthrocentesis is an invasive procedure, and therefore, sterile precautions with a sterile probe cover and gel should always be used.

### Dynamic versus Static Ultrasound Guidance

Like many procedures, ultrasound guidance for arthrocentesis can be performed by either a static or dynamic technique. Static ultrasound guidance involves using the image to identify the synovial space, depth, angle of entry, and vessels/nerves or other obstacles. The sonographer then marks a spot on the skin where success is ...

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