Comparison of magnetic resonance imaging findings with arthroscopic findings in discoid meniscus

It is widely accepted that although valuable in the diagnosis of the discoid meniscus and tears, magnetic resonance imaging (MRI) can be insufficient in determining the type of the tear. This study calculates the sensitivity and specificity of MRI in determining the presence and absence of tears and how these values differ for different types of tears.

This study is a retrospective review of 10 years of our experience with arthroscopic discoid meniscus treatment between 1999 and 2009. MRI findings were compared with the intraoperative arthroscopic findings in 52 patients with 50 lateral and two medial discoid menisci of which 24 were complete and 28 were incomplete. Tears were classified into six groups: (1) no tear, (2) simple horizontal tear, (3) radial tear, (4) combined horizontal tear, (5) complex tear and (6) longitudinal tear. Sensitivity, specificity, positive and negative predictive values of MRI were calculated for each group separately and for the presence and absence of tears in general. In addition, the effect of age, type of discoid meniscus, and presence and absence of shift on the distribution of tear types were analysed.

MRI was found to be 100 % specific and 97.8 % sensitive for determining the presence or absence of a tear with a negative predictive value of 85.7 % and a positive predictive value of 100 %. The specificities were 80 % for simple horizontal, 50 % for radial, 66.7 % for combined horizontal, 55.6 % for complex and 14.3 % for longitudinal tears, whereas the sensitivities were 66.7 % for simple horizontal, 96.9 % for radial, 87.5 % for combined horizontal, 94.6 % for complex and 100 % for longitudinal tears. The presence and absence of shift and type of the discoid were found to affect the distribution of the tear type.

MRI is successful in determining the presence or absence of tears in discoid menisci; however, its ability to determine the tear type is questionable. Complete discoid menisci were found to have tendency towards having a simple horizontal or longitudinal tear, whereas incomplete discoid menisci tend to have radial or combined horizontal tears. Determination of the shift prior to surgery is important since it alters the surgical technique.