The forward displacement of the tibia and the femur is prevented by

Structurally knee is a weak joint because the aicular surfaces are not congruent. The tibial condyles are too small and shallow to hold the large convex femoral condyles in place. The stability of the joint is maintained by a number of factors:-1.cruciate ligaments-anteroposterior stability. 2.Collateral ligaments-side to side stability.3.Iliotibial tractCRUCIATE LIGAMENTS: Very thick and strong fibrous bands. Direct bonds of union between tibia and fibula. Maintain anteroposterior stability of knee joint. Anterior cruciate ligament:- Begins from anterior pa of intercondylar area of tibia, runs upward, backward and laterally and is attached to the posterior pa of medial surface of lateral condyle of femur. Taut during extension of knee. The anterior cruciate ligament is more commonly damaged than the posterior.It may be injured in violent hyperextension of knee or anterior dislocation of tibia. Posterior cruciate ligament:- Begins from posterior pa of intercondylar area of tibia, runs upwards, forwards and medially and is attached to lateral surface of medial condyle of femur. Taut during flexion of knee. The posterior cruciate ligament is injured in posterior dislocation of tibia. Both these are supplied by middle genicular nerves and vessels. {Reference: BDC 6E pg no.143}