Dislocations of the knee are rare. They are true orthopedic emergencies
and have a significant association with soft tissue injuries and
neurovascular compromise. A dislocated knee occurs most commonly
after a major force is applied to the knee joint from motor vehicle
trauma, pedestrian-vehicle collisions, bicycle collisions, or motorcycle
collisions. The forces necessary to cause a dislocation of the knee
joint often fracture the bones of the leg.
Complete dislocation of the knee joint results in a gross deformity
that is confirmed by plain radiographs. Reduction by the Emergency
Physician may be reasonable if the Orthopedic Surgeon is not immediately
available and/or if the injured extremity shows signs of
distal neurologic or vascular compromise.
A careful examination of the distal extremity must be performed
and documented. It must include an assessment
of the capillary refill, the dorsalis pedis pulse, the posterior
tibial pulse, peroneal nerve function, and tibial nerve function.
A knee dislocation is the displacement of the tibiofemoral articulation.
It involves the rupture of the anterior cruciate ligament, the posterior
cruciate ligament, the joint capsule, and/or the collateral
ligaments of the knee. Anterior knee dislocations are the most common
type of knee dislocation. This injury is defined as anterior displacement
of the tibia relative to the femur. It results from an acute hyperextension
injury to the knee joint that ruptures the anterior cruciate ligament completely,
the posterior cruciate ligament partially, and the posterior joint
capsule, allowing for anterior tibiofemoral displacement. The collateral
ligaments usually remain intact. Tibial spine fractures, osteochondral
fractures of the tibia or femur, and meniscal injuries are avulsion-type fractures
resulting from the rupture of the anterior cruciate ligament. Distal
femoral epiphyseal separation, rather than complete dislocation,
as a result of a hyperextension injury is more common in children.
An anterior knee dislocation is associated with a popliteal artery
injury in 30 to 40 percent of patients.1 The popliteal
artery is at particular risk for injury because it is anchored proximally
at the adductor hiatus and distally at the soleus arch. The collateral
circulation around the knee joint is relatively poor. Therefore
disruption of the popliteal artery may result in distal ischemia
and limb loss if the reduction is delayed. It
is important to note that the presence of distal peripheral pulses
and capillary refill does not preclude an arterial injury.
A posterior knee dislocation is defined as the posterior displacement
of the tibia relative to the femur. It occurs less commonly than
an anterior knee dislocation. It results from a direct force applied
to the anterior tibia with the knee slightly flexed, which ruptures
the posterior joint capsule and both cruciate ligaments. The collateral
ligaments usually remain intact. It is associated with popliteal
artery damage and disruption of the extensor mechanism of the knee
A posterolateral knee dislocation is a rare type of knee dislocation
that is associated with peroneal nerve injury in ...