Knee Joint 1

Knee Complex Consists of two distinct articulations namely 2. Tibiofemoral joint 3. Patellofemoral joint • In closed kinematic chain it works in conjunction with hip & ankle to support body weight in static erect posture • In open kinematic chain knee provides mobility for the foot in space •

Tibiofemoral Joint: • Double condyloid joint with 2° freedom of motion • Flexion/extension occur in saggital plane about a coronal axis • Medial/lateral rotation occur in transverse plane about a vertical axis Femoral articular surface: • consists of lateral and medial condyles and an intercondylar notch • medial condyle is slightly longer than the lateral one

Tibial articular surface: • consists of two concave asymmetrical medial and lateral condyles • medial tibial articulating surface is 50% larger than the lateral one • two tibial condyles are separated by a roughened area and two bony spines called as intercondylar tubercles • these tubercles become lodged in the intercondylar notch of femur during knee extension

Articulation: • When condyles of femur are placed on tibial condyles an incongruence develops • Accessory joint structure menisci are present to develop the congruency Menisci: • Asymmetrical fibrocartilage joint disks • Medial is semicircle and lateral is four-fifths of a ring • Both are open towards the intercondylar area,thick centrally,forming concavities • Wedge shaped menisci increase radius of curvature of tibial condyles and there fore joint congruency

Also play an important role in distributing weight bearing forces,reducing friction and serve as shock absorbers • Menisci are attached around its periphery to tibial condyle by coronary ligament •

Anterior horns are joined to each other by transverse ligament • Menisci are rich with free nerve endings and three different mechanoreceptors and hence act as a source of information about joint position, direction of movement and velocity of movement •

Menisci are important in distributing and absorbing large forces crossing the knee joint • Ordinarily compressive forces in the dynamic knee may reach 2-3 times body weight in normal gait and 5-6 times in activities such as running and stair climbing • Menisci assume 40% – 60% of the imposed load •

Tibiofemoral alignment & weight bearing forces: • Anatomic axis of femur is oblique directed inferiorly and medially from proximal to distal end • Anatomic axis of tibia is also directed almost vertically • Both axes normally form an angle medially at knee of 185°-190°,femur is angulated off vertical 5° -10° creating a normal valgus angle at knee

•

Mechanical axis of lower limb is weight bearing line from center of head of femur to superior surface of head of talus

Because weight bearing line follows mechanical rather than anatomic axes, the weight bearing stresses on the knee in bilateral stance are equally distributed between medial and lateral condyles • Deviations in normal force distribution may be caused by an increase or decrease in normal tibiofemoral angle •

If medial angle is greater than 195° Genu Valgum (knock knees) • This will increase compressive force on lateral condyle while increasing tensile stresses on medial structures •

If medial angle is 180° or less Genu Varum (bow knees) • This will increase compressive forces on medial condyle while increasing tensile stresses on lateral structures •

•

Constant overloading of stresses result in damage to cartilage