Objective  To identify the MR image type of mediopatellar plica by comparing direct MR arthrography  with arthroscopy findings.   Methods  The MR image and arthroscopic findings of 67 patients were retrospectively compared. Among them

33 cases (Group A)who underwent diagnostic and operative video arthroscopy and diagnosed as mediopatellar plica were divided to 4 types according to Sakakibara’s criteria. Then the width of their plica on MR image were measured and the results were compared with anthroscopic findings. Another 34 patients (Group B) receiving MR image examination were divided according to the width of plica

then the results were further testified when undergoing arthroscopy.   Results  In group A

the width of type A plica was (0.226±0.039)

type B (0.463±0.053)

type C (0.738±0.037)

and type D (0.825±0.026). There was significant difference between type A and type C

and type B and type C. In group B

the agreement Kappa test and Wilcoxon signed rank test showed that the type diagnosis made by MRA was almost concordance with that of arthroscopy (Kappa0.6

P0.05).   Conclusion  The features of  direct MR arthrography is coordinate with the arthroscopic findings in mediopatellar plica. MRA is a valuable diagnostic technique

and a very important examination before arthroscopy for mediopatellar plica syndrome.