Contributor:  Erik Verzemnieks, MD Educational Pearls: Knee dislocations are most common in high energy trauma, such as a motor vehicle accident The knee may appear grossly normal on initial inspection since dislocations can spontaneously reduce - Look for such findings as hemarthrosis, instability, or ecchymosis, as clues to an occult dislocation.  Knee dislocations are often associated with damage to the popliteal artery that runs behind the knee.  Assess for pulse deficit on exam. If you are concerned - use the ankle-brachial index (normal >0.9). If the ABI is abnormal, evaluate with CT angiogram and a vascular surgery consult.    References Mills WJ, Barei DP, McNair P. The value of the ankle-brachial index for diagnosing arterial injury after knee dislocation: a prospective study. J Trauma. 2004 Jun;56(6):1261-5. Steele HL, Singh A. Vascular injury after occult knee dislocation presenting as compartment syndrome. J Emerg Med 2012; 42:271. Sillanpää PJ, Kannus P, Niemi ST, et al. Incidence of knee dislocation and concomitant vascular injury requiring surgery: a nationwide study. J Trauma Acute Care Surg 2014; 76:715. Summarized and written by myself