The menisci are two crescentic fibrocartilaginous structures made predominantly of Type 1 collagen. The collagen bundles are arranged in a circumferential pattern that is optimal for absorption of compressive loads. Radial fibres are woven between the circumferential fibres, which help to provide structural integrity.
The arrangement of the collagen fibres enables them to resist the hoop stresses that are produced at the meniscus during weight bearing.
The menisci are triangular in cross section, the peripheral border of each meniscus being thick, convex, and attached to the capsule of the joint and the opposite border tapering to a thin, free edge. The posterior horn of the medial meniscus is larger than the anterior horn, whereas the anterior and posterior horns of the lateral menisci are typically of similar size. The proximal surfaces of the menisci are concave and in contact with the femoral condyles; the distal surfaces are flat and rest on the tibial plateau. The medial meniscus covers approximately 64% of the medial tibial plateau. The lateral meniscus covers approximately 84% of the lateral tibial plateau.
Embryologically, the menisci form from mesenchymal tissue and appear as distinct structures by the eighth to tenth week of gestational development. Initially highly cellular, the perinatal meniscus also has an abundance of blood vessels. Progressive and gradual changes occur from birth to mid-adolescence, consisting of decreasing cellularity, decreasing vascularity, and increasing collagen content.
The medial meniscus is firmly attached to the posterior intercondylar fossa of the tibia directly anterior to the PCL insertion.
The lateral meniscus anterior horn is attached to the intercondylar fossa, directly anterior to the lateral tibial tubercle and adjacent to the ACL. The posterior horn is attached to the intercondylar fossa directly posterior to the lateral tibial tubercle and anterior to the posterior horn of the medial meniscus. the meniscofemoral ligaments, connect the posterior horn of the lateral meniscus to the intercondylar wall of the medial femoral condyle.
Peripherally, the medial meniscus is continuously attached to the capsule of the knee. The tibial attachment of the meniscus, sometimes known as the coronary ligament, attaches to the tibial margin a few millimeters distal to the articular surface. The anterior horn of the medial meniscus has the largest insertion site surface area (61.4 mm2), and the posterior horn of the lateral meniscus has the smallest (28.5 mm2).The anterior attachment is more variable (4 Types described by Ohkoshi) -
Classic Fairbank's signs postmeniscectomy - squaring of femoral condyle, joint space narrowing and osteophytes.
Thompson (1991) studied meniscal motion with 3-dimensional MRI and cinematic MRI. Medial meniscal excursion was approximately 5.1 mm, and lateral meniscal excursion, 11.2 mm. The posterior horn excursion has been noted to be less than that of the anterior horn, both medially and laterally. DePalma has demonstrated that most lateral meniscal motion occurs after 5 to 10 degrees of flexion, whereas most medial meniscal displacement occurs after 17 to 20 degrees of flexion. The posterior oblique ligament is firmly attached to the posterior medial meniscus, thereby limiting its displacement and rotation. This possibly accounts for the increased risk of injury to the medial meniscus. Conversely, the relatively increased mobility of the lateral meniscus is also responsible for the more frequent occurrence of injuries on the medial side.
The meniscus in a neonate is entirely vascular. By the age of 10, the meniscal vascularity is similar to the adult meniscus. Studies by Arnoczky and Warren have demonstrated that only the outer 10% to 25% of the lateral meniscus and 10% to 30% of the medial meniscus are vascular.These vessels are derived from the middle, medial, and lateral geniculate arteries. The inner two thirds of the meniscus is avascular and is nourished by the synovial fluid through diffusion.
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Our knowledge and under- standing of the anatomy and function of the meniscus has evolved significantly over the past few decades.
This understanding combined with advances in arthroscopic surgery, have dramatically changed our surgical philosophy.
Open total meniscectomy is no longer acceptable treatment, Commonly accepted treatment of meniscal disorders now include arthroscopic partial meniscectomy, as well as meniscal repair. Efforts are now increasingly directed at meniscal preservation and even restoration