[An analysis of meniscal extrusion and associated knee joint lesions by magnetic resonance imaging]

We investigated the frequency of meniscal extrusion and associated knee joint lesions by magnetic resonance imaging (MRI) in patients with meniscal tears.

We retrospectively evaluated MRI findings of 100 patients (41 males, 59 females; mean age 54 + or - 10 years; range 27 to 76 years) with meniscal tears in 126 knee joints. Using coronal images, extrusion was defined as a distance of = or > 3 mm between the peripheral border of the meniscus and the edge of the tibial plateau. All the knees were assessed with respect to the localization and type of meniscal tear and extrusion, accompanying joint effusion, cruciate ligament pathologies, and degenerative bone and cartilage changes.

Meniscal extrusion was detected in 31 knee joints (24.6%), with a mean extrusion of 3.72 mm. All extrusions were found to be in the posterior horn of the medial meniscus and were associated with radial tears (n=18, 58.1%), radial-oblique tears (n=9, 29%), complex tears (n=2, 6.5%), and flap tears (n=2, 6.5%). Meniscal tears with extrusion differed significantly from those without extrusion with respect to the localization of all the tears being in the posterior horn of the medial meniscus (100% vs. 60%) and the higher frequency (58.1% vs. 20%) of radial tears (p<0.05). There were no significant differences in the types and frequencies of accompanying pathologies seen in meniscal tears with and without extrusion (p>0.05).

Meniscal extrusion is a common finding particularly in osteoarthritis. It is mostly seen in the medial meniscus and accompanied by radial tears. Therefore, its presence should alert to the possibility of a radial tear extending to the meniscal root.