A healthy young athlete is sitting at the edge of the table with knee at 90-degree flexion. He fully extends it. What will happen?
In full extension the knee gets locked, which involves lateral rotation of tibia (since foot is off the ground). Hence, tibial tuberosity moves laterally towards the lateral border of patella. Physiological Knee locking happens in the last 30deg of knee extension and involves the rotation of either bone femur or tibia. a. It involves medial rotation of femur on tibia if the foot is fixed to the ground (weight bearing leg). b. If the foot is off the ground (as sitting on a table) then tibia has to rotate opposite (laterally) to lock the knee joint. Knee locking happens when we stand straight or straighten our lower limb in the air (e.g., during some exercise) a. It is the most stable position of the knee joint b. Femur & tibia are locked on to each other and there is maximum congruency between the two. c. Almost all ligaments are tightened and provide maximum stability to the joint. IV. Quadriceps femoris leads to knee extension and knee locking happens due to the continued action of quadriceps femoris. V. Unlocking of knee joint is carried out by popliteus muscle. a. It involves the rotation of any of the two bones (femur/tibia) in opposite direction to locking. b. Popliteus muscle is a very small muscle at the floor of popliteal fossa and is supplied by the tibial nerve. c. Popliteus has intracapsular origin. Pathological knee locking: It is an ohopaedic problem where patient has some meniscal injury and he finds difficulty in carrying out knee extension fully. Ref - The physiology of the joints (5th Ed.) ,Vol-2 Pg. 102,103 .
Movement of tibial tuberosity towards centre of the patella
Movement of tibial tuberosity towards lateral border of patella
Movement of tibial tuberosity towards medial border of patella
No change in position
Lower limb