Hillary Elizabeth Boortz MD, Presenter: Nothing to Disclose

Kambiz Motamedi MD, Abstract Co-Author: Nothing to Disclose

Miriam Parsa, Abstract Co-Author: Nothing to Disclose

Benjamin David Levine MD, Abstract Co-Author: Nothing to Disclose

Leanne Louise Seeger MD, Abstract Co-Author: Nothing to Disclose

Deborah McCurdy, Abstract Co-Author: Nothing to Disclose

Knee effusions commonly occur with injury or inflammation.  Imaging is more accurate in detecting small amounts of joint fluid compared with clinical examination.  MRI in particular is extremely sensitive for detecting effusions.  Cadaveric studies have demonstrated that in the supine position an effusion tends to pool laterally in the knee.  The purpose of this paper is to further localize the fluid distribution of knee effusions in patients on MR imaging, which can be used to optimize assessment of effusions with sonography.

We retrospectively reviewed 80 knee MRIs of adult outpatients (ages 18-80) who were reported to have a joint effusion and no history of prior surgery or fracture.  All knees were imaged on a 3T MR scanner.  On axial fat-saturated T2 weighted images, using standardized PACS measurement tools, the thickest area of fluid collection in the midline, medial, and lateral recesses of the central and/or suprapatellar synovial compartments was measured.  Statistical analysis was performed using a paired T-test.

The fluid thickness in the lateral recess of the synovial compartment with an average thickness of 7.5 mm, was significantly more prominent than centrally, averaging 6.7 mm (p<0.02).  The fluid thickness in the medial recess, averaging 5 mm, was significantly less than centrally (p<0.01).

A significantly larger amount of fluid accumulates in the lateral aspect of the central and suprapatellar synovial recesses when compared to the midline and medial aspects on knee MRI.  Ultrasound traditionally relies on the appearance of the suprapatellar recess at midline to assess for a knee joint effusion.  Our results suggest that in order to avoid underestimating the presence or size of a knee effusion, sonographic evaluation of the knee joint should routinely include an assessment of the lateral recess.

Predominant distribution of intraarticular fluid into the lateral recess in supine patients with knee effusion on MRI is relevant and applicable to sonographic evaluation of the joint for effusion.

Boortz, H, Motamedi, K, Parsa, M, Levine, B, Seeger, L, McCurdy, D, Comparative Measurements of Fluid Thickness on Knee MRI in the Midline vs Lateral Recesses: Where to Look for a Knee Joint Effusion with Ultrasound.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11004243.html