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Can you name the key structures/layers in this transverse suprapatellar image of the knee??

Below are the major structures of interest labeled in this transverse suprapatellar knee ultrasound image. 

Image 3: Image courtesy of Matthew Negaard, author’s own annotations

Can you label the structures in the transverse suprapatellar ultrasound image of the knee?

What is your diagnosis

This is a knee effusion as seen in the suprapatellar recess. 

1. Bonus: the quadriceps tendon in this case is severely inflamed and much less compact than traditional. In the patient used for this image, there was significant concern for septic arthritis. There is also debris in the effusion which suggests an infectious process as well. 

2. Pro Tip: The amount of muscle and size of quadricep tendon seen will be proportional to how close you are to the patella with your transverse view with more muscle and less tendon as you scan proximally.

How would you perform an ultrasound guided arthrocentesis of the knee joint?

Steps for ultrasound guided knee arthrocentesis (see GIFs below for examples):

1. Place the probe in a transverse fashion in the suprapatellar area. 

2. Identify the effusion. 

1. For a native knee, this effusion will lie between the prefemoral fat pad and the suprapatellar fat pad (which lies underneath the quadriceps tendon)

2. For a total arthroplasty (like our case had), the prefemoral and suprapatellar fat pads may be removed to a varying degree and it may be hard to identify them

3. Mark the lateral thigh based on the depth of the anechoic fluid seen on the ultrasound

4. Using an in-plane approach, guide the needle under US-guidance, aspirating as you go. 

5. As you visualize the needle in the anechoic fluid, you should be getting synovial fluid return

Image 6: Author’s own images. Demonstration of the tissue layers moving around the effusion with external lateral pressure

Image 7: Author’s own images. Needle tracking into the effusion