Extensor mechanism of knee

short ppt on extensor mechanism of knee

1. EXTENSOR MECHANISM OF KNEE

2. INTRODUCTION The knee joint is one of the largest and most complex joints in the body. It is constructed by 4 bones and an extensive network of ligaments and muscles

3. Tibia femoral joint rotation translations screw home mechanism Axial & rotation alignment of the knee Patello femoral joint

4. Quadriceps muscles Rectus femoris Vastus lateralis Vastus intermedius Vastus medialis

5. Rectus femoris L2L3L4 Hip flexion and knee extension profunda Vastus mediuc L2L3L4 Vastus intermedius L3>L2L4 knee extension femoris Vastus lateralis L3>L2L4 artery

6. ANTERIOR LAYER : Direct attachment by RF to patella INTERMEDIATE LAYER : By attachment of VM and VL VL blended with the lateral patellar retinaculum and direct tibial insertion VM is more distally attached to patella DEEP LAYER :Formed by tendon of vastus intermedius

7. Patello tibial tendon attached to tibial tuberosity

8. T he primary function of the patella is to increase the lever arm of the extensor mechanism around the knee, improving the efficiency of quadriceps contraction

9. The extensor lever arm is greatest at 20 degrees of flexion and the quadriceps force required for knee extension increases significantly in the last 20 degrees of extension

10. The length of lever arm varies as a function of geometry of trochlea varying petallo femoral contact areas and the varying centre of rotation of knee

11. OPEN KINETIC CHAIN- d uring knee extension, tibia glides anteriorly on femur. more precisely, from 20  knee flexion to full extension, tibia rotates externally. During knee flexion, tibia glides posteriorly on femur and from full knee extension to 20  flexion, tibia rotates internally Closed kinetic chain  - d uring knee extension, femur glides posteriorly on tibia. to be more specific, from 20  knee flexion to full extension, femur rotates internally on stable tibia. during knee flexion, femur glides anteriorly on tibia and from full knee extension to 20  flexion, femur rotates externally on stable tibia.

12. The "screw home mechanism" the "screw-home" mechanism, considered to be a key element to knee stability, is the rotation between the tibia and femur. it occurs at the end of knee extension, between full extension (0 degrees) and 20 degrees of knee flexion. the tibia rotates internally during the open chain movements (swing phase) and externally during closed chain movements (stance phase). external rotation occurs during the terminal degrees of knee extension and results in tightening of both cruciate ligaments, which locks the knee. the tibia is then in the position of maximal stability with respect to the femur

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