Knee Dislocations:

Are relatively rare injuries, but can result in loss of the limb if missed.  Patients will sometimes say they dislocated their knee when they actually mean their patella, so a good history where they describe what their knee looked like, and what they were doing at the time will help differentiated the two.

Some signs that you are dealing with a spontanously reduced knee dislocation are:

• Varus or valgus instability in full extension of the knee is suggestive of a grossly unstable knee
• Pain out of proportion to injury
• Absent or decreased pulse

The loss of limb is due to unrecognized injury to the popiteal artery which as be estimated to occur 7-45% of the time. 

• Normal pulses and a normal capillary refill does NOT rule out as significant vascular injury. 
• Arteriograms are no longer mandatory in all cases, but it is generally recommended that you perform an ankle-brachial index and get a vascular duplex scan of the popiteal artery to exclude dissections, tears, aneurysms and psuedo-anuerysms that can all occur as a result of the dislocation.

If you would like to see some videos of knee injuries in the making follow this link www.csmfoundation.org/Educational_Lower_Extremity.html