<prompt> Commonest dangerous complication of posterior dislocation of knee is-Popliteal aery injurySciatic nerve injuryIschaemia of lower leg compamentFemoral aery injury  <response>: Dislocation of the knee- This rare injury results from severe violence to the knee so that all of its suppoing ligaments are torn. It is a major damage to the joint, and is often associated with injury to the popliteal aery. Treatment is by reduction followed by immobilization in a cylinder cast. Clinical evaluation : vascular exam -Measure Ankle-Brachial Index ABI if ABI 0.9 then monitor with serial examination if ABI 0.9 -If pulses are absent or diminished confirm that the knee joint is reduced or perform immediate reduction and reassessment - Immediate surgical exploration if pulses are still absent following reduction ;schema time 8 hours has amputation rates - If pulses present after reduction then measure ABI then consider observation vs. angiography Clinical evaluation : vascular exam -Priority is to rule out vascular injury on exam both before and after reduction serial examinations are mandatory. - Palpate the dorsalis pedis and posterior tibial pulses if pulses are present and normal , it does not indicate absence of aerial injury. Ref: Maheshwari 9th ed p.142 