The anteroposterior elevation between the tibial condyles corresponds to the femoral intercondylar notch. If the surfaces of the tibial condyles are projected anteriorly, they coincide with the articular surface of the patella which corresponds to, and is almost congruent with, the anterior surfaces of the femoral condyles. If the intercondylar eminence of the tibia is projected anteriorly, its plane is continuous with the vertical ridge on the patella just as the intercondylar notch of the femur continues in the central groove of the patellar surface of the femur. This arrangement resembles a twin-wheel rolling on a central rail (Fig. 1a). During flexion and extension, tibia and patella act as one structure in relation to the femur.1 The rounded surfaces of the femoral condyles in relation to the flatter tibial ones might suggest that the former roll during flexion–extension. In fact this is not so. As long ago as 1836 the Weber brothers demonstrated that the femoral condyles roll and slide almost simultaneously, and that these movements are in opposite directions. During flexion, the femoral condyles roll backwards and slide forwards on the tibia, whereas during extension they roll forwards and slide backwards (see Standring, Fig. 82.20). The ratio of rolling to sliding differs with the degree of flexion or extension, which means that during the first 30° of flexion the movement is almost entirely rolling, whereas at nearly full flexion the condyles slip over the tibial plateau without rolling.2 There are two menisci in the space between the femoral and tibial condyles. They are crescent-shaped lamellae, each with an anterior and a posterior horn, and are triangular in cross section. The superior and inferior surfaces are in contact with the femoral and tibial condyles, respectively, and the peripheral surfaces are adherent to the synovial membrane of the capsule. The anterior and posterior horns are anchored to the tibial condyle in the anterior and posterior intercondylar fossae, respectively. The horns of the medial meniscus are further apart than those of the lateral, which makes the former nearly semilunar and the latter almost circular. The menisci correct the lack of congruence between the articular surfaces of tibia and femur, increase the area of contact and improve weight distribution and shock absorption.3–6 They also help to guide and coordinate knee motion, making them very important stabilizers of the knee. Movement between the tibial surface and the menisci is limited by the coronary ligaments connecting the outer meniscal borders with the tibial edge (Fig. 3, see Standring, Fig. 82.9). The coronary ligaments of the medial meniscus are shorter (4–55 mm) and stronger than those of the lateral meniscus (13–20 mm).7 The medial collateral ligament of the knee is attached by its deep fibres to the outer border of the medial meniscus. In contrast, there is no connection between the lateral meniscus and the corresponding collateral ligament (Fig. 4). These anatomical differences between the medial and the lateral meniscus may explain the lesser mobility and the greater vulnerability of the former (see Fig. 3).8 Menisci do not contain pain-sensitive structures and are consequently insensitive to trauma. Their outer third has some blood supply and therefore a slight ability to heal. The inner non-vascularized part receives nutrition through diffusion of synovial fluid.9,10
Applied anatomy of the knee
Articular surfaces
The menisci
anatomy of the knee
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