<prompt> Commonest dangerous complication of posterior dislocation of knee is -Popliteal artery injurySciatic nerve injuryIschaemia of lower leg compartmentFemoral artery injury  <response>: Dislocation of the kneeThis rare injury results from severe violence to the knee so that all of its supporting ligaments are torn.It is a major damage to the joint, and is often associated with injury to the popliteal artery.Treatment is by reduction followed by immobilization in a cylinder cast. 