Circumferential collagen fibers in menisci absorb compressive forces, resisting longitudinal loading (hoop stress) and meniscal extrusion. The normal hoop tension for the meniscus is reduced by radial tears that extend to the capsular margin of the meniscus. Functionally speaking, the loss of hoop tension of a meniscus is equivalent to total meniscectomy and leads to early degenerative change.
Root tears are more commonly seen in the posterior horn of the medial meniscus. Complete radial tear of the medial meniscus root leads first to meniscal extrusion and subsequently to the development of osteoarthritis. The image above shows a complete radial tear of the posterior root of the medial meniscus on the coronal image (pink arrow) with a ghost meniscus on the sagittal image (white arrow held by Casper) and meniscal extrusion (blue arrow). Bone marrow T2 hyperintensity is seen in the medial femoral condyle and the medial tibial plateau, with loss of articular cartilage at the medial compartment and a small subchondral fracture at the medial tibial plateau.