Thomas Magee, Presenter: Nothing to Disclose

David S. Williams MD, Abstract Co-Author: Nothing to Disclose

Meniscal extrusion (greater than 3mm extension beyond the tibial margin) has been described on previous studies as having a high index of association with meniscal root tears. These previous studies were limited by a lack of exact arthroscopic correlation. We correlated MR exams with meniscal extrusions greater than 3 mm beyond the tibial margin and correlated MR findings with arthroscopic findings.

A retrospective review of 300 consecutive knee MR exams was performed. All patients had a complete MR exam performed on a 3 Tesla GE MR. MR exams were reviewed for medial meniscal extrusion greater than 3 mm from the tibial margin.

Forty two of the MR exams demonstrated medial meniscal extrusion greater than 3 mm from the tibial margin. Thirty three of these patients had meniscal degeneration, complex tear or a large radial tear involving the meniscal root on arthroscopy. Nine of these patients had no meniscal tear demonstrated on arthroscopy despite MR findings consistent with degenerative tearing at the meniscal root using currently accepted MR criteria for such.. Four of the nine arthroscopy reports indicated there was no evidence of medial subluxation of the meniscus. All nine of these patients were fifty years or greater in age.

There may be a subset of patients in which the meniscal root is stretched rather than torn. Additionally there may be some dynamic subluxation of the meniscus resulting in intermittent extrusion. This is not evident on static MR images but is evident on arthroscopy. Medial meniscal extrusion in patients greater than age 50 may be a significant source of false positive readings of meniscal tears on MR examinations as compared with arthroscopy.

Magee, T, Williams, D, MR Findings of Extruded Medial Menisci Correlated with Arthroscopy.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4407451.html