The role of meniscal root pathology and radial meniscal tear in medial meniscal extrusion.

OBJECTIVE: The purpose of our study was twofold: to better understand the relationship between medial meniscal extrusion (MME) and degenerative joint disease (DJD), and to determine whether a relationship exists between MME and medial meniscal root (MMR) pathology, radial tear and joint effusion.

DESIGN AND PATIENTS: Two hundred and five consecutive MR imaging examinations of the knee were prospectively evaluated, regardless of indication, for the presence and degree of MME, medial compartment marginal osteophytes, medial compartment articular cartilage loss, joint effusion, medial meniscal tear and MMR pathology. MME >or=3 mm was considered abnormal. All studies were performed using a 1.5 T GE Signa MR unit with a quadrature knee coil. The standard protocol included oblique sagittal, coronal and axial imaging.

RESULTS: We found a strong association ( P<0.0001) between >or=3 mm MME and medial joint line osteophytosis (77%), medial compartment articular cartilage loss (69%), MMR pathology (64%) and radial tear (58%) when compared with knees without these findings. Fifty-one percent of cases with a moderate/large joint effusion had <3 mm MME. We found that 20% (31/155) of patients with minimal or no evidence of DJD had >or=3 mm MME. Of this group, 62% (19/31) had either MMR pathology and/or radial tear, 13% (4/31) had joint effusion as their only abnormality and 6% (2/31) had a normal examination (other than the presence of MME). The remaining 19% consisted of three cases of different types of meniscal tear and three cases of small joint effusions but no other detectable pathology.

CONCLUSION: MME >or=3 mm is strongly associated with DJD, MMR pathology and radial tear. A significant number of cases with no or minimal evidence of DJD (20%) had >or=3 mm MME, suggesting that MME precedes, rather than follows, the development of DJD. We also found that joint effusion was not strongly associated with >or=3 mm MME.