It is not uncommon for a patient to have dislocated their knee and it to spontanously reduce prior to presenting to the ED.
Consider the possibility of a spontaneously reduced knee dislocation in any patient with bicruciate (ACL and PCL) ligament instability.
Normal pulses and capillary refill does not exclude occult vascular injury to the popiteal artery.
At a minimum the patient should have Ankle Brachial Indexs performed and if <0.9 serial exams and Doppler ultrasound studies should be obtained.
Angiography is not absolutely required, and several studies have shown that a selective approach to angiography is acceptable. As the studies below showed, most patients with findings requiring operative repair on angiography had abnormal physical exams.
References
Klineberg EO, Crites BM, Flinn W, et al: The role of arteriography in assessing popliteal artery injury in knee dislocations. J Trauma. 2004 Apr;56(4):786-90.
Hollis JD, Daley B, et al: 10-year review of knee dislocations: is arteriography always necessary? J Trauma. 2005 Sep;59(3):672-5.
