KTJ comparison

notes notes notes notes radiological profile joint tracing radiologica l profile joint tracing radiological profile jointtracing radiologica l profile joint tracing During flexion up to 30-35°, the KTJ hinge permits rotation around the initial centre of rotation; as flexion continues, this action gradually combines with a linear movement which imitates the anterior slide of the femur on the tibia thus reproducing the rotation translation that is characteristic of the knee The tr ajector y of the hinge with a variable centre of rotation r eproduces precisely the physiological knee movement thr oughout the entire f lexion-extension y Thehingewit ha fix edcentreofrota tion is composed of a central axis around which there is rotation. Thehinge with2 centresofrotation develops rotationsimultaneously around2 centresof rotation leading to an inversely cyclical trajectory. With this hinge, during the first 25° of flexion, the central axis placed in correspondence with the initial centre of rotation, carries out anterior translation. Itrotatesarou ndtheaxisplacedonthe periph eralcent erofrotationandsimula tes anterior sliding of the head of the femur. After 25° the centre of rotation “skips” toa centralaxisdetermining arotation whichcontinuesuntil themaximum degrees of flexion. Thus there is a translation-rotation movement. 0 30° 60° 90° 110° 0 30° 60° 90° 110° 0 30° 60° 90° 110° X 1 y Y 1 From the beginning of flexion, the hinge tracing tends to move backwards with regard to the radiological profile. Towards maximum flexion the hinge tracing is actually behind and below the flat articulator surfaces of the tibia. Y Y 1 -X 1 X Y - Y 1 X 1 X Y 1 Y X 1 X A correct movement is maintained until 30-35 0 of flexion. Beyond that the hinge tracing tends to move vertically (Y1) away from the radiological profile of the knees physiological trajectory. Y<Y1 ! ! t r a c t i o n Y<Y1 X>X1 ! ! t r a c t i o n o n a l l a x i s Y>Y1 X<X1 ! ! t r a c t i o n a n d c o m p r e s s i o n 0 30° 60° 90° 110° x= y Y X 1 X Y 1 Y=Y1 X=X1 c o r r e c t m o v e m e n t ! Comparisionbetweentheradiological profileand thejoint tracingobtained using 1 a hinge with a variable centre of rotation Comparisionbetweentheradiological profileand thejoint tracingobtainedusing Comparisionbetweentheradiological profileand thejoint tracingobtainedusing Comparisionbetweentheradiological profileand thejoint tracingobtainedusing 3 a hing with 2 centres of rotation 4 a hing with skipping centre of rotation At the beginning of the movement, the hinge tracing (-X1) moves backwards dramatically in comparison to the radiological profile and as flexion continues the hinge tracing moves away vertically as well. 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 40 41 42 43 44 39 45 46 47 61 62 64 65 66 67 68 63 69 70 71 72 73 74 75 76 78 79 80 81 82 77 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 17 19 20 21 16 22 23 24 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 40 41 42 43 44 39 45 46 47 61 62 64 65 66 67 68 63 69 70 71 72 73 74 75 76 78 79 80 81 82 77 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 17 18 19 20 21 16 22 23 24 2 a hinge with a fixed centre of rotation H w t h b l f i

KTJ comparison

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