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Lecture-2 Located between the body’s two largest lever arms. Susceptible to injury. Largest motion in the sagittal plane. In extension, rotation limited by interlocking of tibial and femoral condyles. Rotation increases as the knee is flexed, reaching maximum at 90 degrees. Ext. rot 0-45 Int. rot 0-30 Beyond 90 degrees, range of int & ext rot is decreased due to soft tissues. Limited abd & add in full extension Increases with knee flexion up to 30 degrees. Motion in frontal plane again decreases beyond 30 degrees due to soft tissues. Range for ADLs= full ext to 117 degrees of flexion. The asymmetrical medial and lateral tibial condyles or plateaus constitute the distal articular surface of the knee joint The medial tibial plateau is longer in the anteroposterior direction than is the lateral plateau; however, the lateral tibial articular cartilage is thicker than the articular cartilage on the medial side. The proximal tibia is larger than the shaft and, consequently, overhangs the shaft posteriorly Accompanying this posterior overhang, the tibial plateau slopes posteriorly approximately 7° to 10°. The medial and lateral tibial condyles are separated by a roughened area and two bony spines called the intercondylar tubercles These tubercles become lodged in the intercondylar notch of the femur during knee extension. The tibial plateaus are predominantly flat, with a slight convexity at the anterior and posterior margins, which suggests that the bony architecture of the tibial plateaus does not match up well with the convexity of the femoral condyle. Because of this lack of bony stability, accessory joint structures (menisci) are necessary to improve joint congruency. The anatomic (longitudinal) axis of the femur, as already noted, is oblique, directed inferiorly and medially from its proximal to distal end. The anatomic axis of the tibia is directed almost vertically. Consequently, the femoral and tibial longitudinal axes normally form an angle medially at the knee joint of 180° to 185°; that is, the femur is angled up to 5° off vertical, creating a slight physiologic (normal) valgus angle at the knee If the medial tibiofemoral angle is greater than 185, an abnormal condition called genu valgum (“knock knees”) exists. If the medial tibiofemoral angle is 175° or less, the resulting abnormality is called genu varum (“bow legs”). Each condition alters the compressive and tensile stresses on the medial and lateral compartments of the knee joint. An alternative method of measuring tibiofemoral alignment is performed by drawing a line from the center of the femoral head to the center of the head of the talus This line represents the mechanical axis, or weight bearing line, of the lower extremity, and in a normally aligned knee, it will pass through the center of the joint between the intercondylar tubercles. The weight-bearing line can be used as a simplification of the ground reaction force as it travels up the lower extremity. In bilateral stance, the weight-bearing stresses on the knee joint are, therefore, equally distributed between the medial and lateral condyles (or medial and lateral compartments). However, once unilateral stance is adopted or dynamic forces are applied to the joint, compartmental loading is altered. In the case of unilateral stance (e.g., during the stance phase of gait), the weight-bearing line must shift medially across the knee to account for the now smaller base of support below the center of mass This shift increases the compressive forces on the medial compartment Abnormal compartmental loading may be also be caused by frontal plane malalignment (genu varum or genu valgum). Genu valgum, for instance, shifts the weight-bearing line onto the lateral compartment, increasing the lateral compressive force while increasing the tensile forces on the medial structures whereas the tensile stresses are increased laterally The presence of genu valgum or genu varum creates a constant overload of the lateral or medial articular cartilage, respectively, which may result in damage to the cartilage and the development of frontal plane laxity. Genu varum, for instance, may con-tribute to the progression of medial compartment knee In the case of genu varum, the weight-bearing line is shifted medially, increasing the compressive force on the medial condyle, causes osteoarthritis and lead to excessive medial joint laxity as the medial capsular ligament’s attachment sites are gradually approximated through the erosion of the medial compartment’s articular cartilage. Thank you