Factors affecting meniscal extrusion: correlation with MRI, clinical, and arthroscopic findings.

The existence of meniscal extrusion is well known in the natural history of the osteoarthritic knee. However, extruded menisci are also seen in non-pathologic knees. To ascertain the prevalence of meniscal extrusion in non-arthritic patients, the MRIs of 100 knees were prospectively studied. The data were correlated both with clinical and operative arthroscopic findings. The results showed 68.5% of the medial menisci to have some degree of extrusion, averaging at 28% of the meniscal size. While the lateral meniscus were extruded in 18.8% of cases at an average of 15% of the meniscal size. Furthermore, a relationship between the anterior insertion variant of the anterior medial meniscus and meniscal extrusion was found (P=0.001) in this series. The results suggest meniscal extrusion to be much more common in non-arthritic knees than previously estimated. The results also suggest that when the anterior horn of the medial meniscus inserts anteriorly in the tibial plateau, the meniscus tends to be extruded. It must be kept in mind that one of the limitations of this work is that the MRIs are taken in a non-weightbearing position.