MENISCAL POSITION ON ROUTINE MR-IMAGING OF THE KNEE

Objective. To determine the prevalence of meniscal protrusion (i.e. lo cation of the outer edge of a meniscus beyond the tibial articular sur face), and to determine its relationship with internal derangement, jo int effusion, and degenerative arthropathy. Design and patients. Sagit tal and coronal MR images of 111 abnormal and 46 normal knees were eva luated for the presence of meniscal protrusion. We set 25% as the mini mum amount of displacement considered abnormal because this was the sm allest amount of displacement we could confidently discern. Presence o f meniscal tear, anterior cruciate ligament (ACL) injury, joint effusi on, or osteophytosis was also recorded. Results and conclusion. Normal examinations demonstrated protrusion of the medial meniscus in 6.5% o f sagittal images and 15% of coronal images, and of the lateral menisc us in 2% and 13%, respectively. Fisher's exact test demonstrated a sta tistically significant difference between the normal and abnormal grou ps for the medial meniscus on both sagittal (P<0.0001) and coronal (P= 0.01) images, but not for the lateral meniscus in either plane (P>0.2) . A protruding medial meniscus was associated with effusion and osteop hytosis (P<0.05) but not with meniscal or ACL tear (P>0.1). Posterior protrusion of the lateral meniscus was only associated with ACL injury (P<0.0001); protruding anterior horns and bodies of lateral menisci w ere not associated with any of the four abnormalities. It is concluded that the medial meniscus may occasionally protrude mere than 25% of i ts width, but protrusion is more often due to effusion and osteophytes . Protrusion of the posterior horn of the lateral meniscus is associat ed with ACL insufficiency, while protrusion of the body and anterior h orn of the lateral meniscus is a normal variant.