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.
