Knee (tibiofemoral) Dislocation

-MVC is most common mechanism 

-Many dislocations self reduce prior to ED presentation so high clinical suspicion is paramount 
     -If diminished pulse on exam, reduce immediately!

-Popliteal artery injury more common with posterior dislocation (44% of time)
     -Check ABI (ankle-brachial index) with all dislocations/suspected dislocations
     -ABI < 0.9: needs CT angiogram of leg and vascular surgery consult 
     -ABI > 0.9: no immediate imaging necessary, monitor for serial vascular exams 

-Examine for common peroneal nerve injury (foot drop and sensory deficits on the dorsum of foot).  Incidence up to 50%.  

-Consult orthopedics, posterior splint/knee immobilizer, observe for serial neurovascular checks and compartment syndrome if no indication for immediate surgical repair 

Reference: Arnold C, Fayos Z et. al.  Managing Dislocation of the Hip, Knee and Ankle in the Emergency Department.  Emergency Medicine Practice. Dec 2017, Vol 19, Number 12.