Knee dislocation

Background

Can result from high- or low-velocity injuries (MVC, martial arts, water-skiing)

Anterior, posterior, medial, lateral, or rotatory dislocations all possible

Anterior requires 30o of hyperextension before joint failure

Posterior usually a dashboard injury

Requires failure of three ligaments

Popliteal artery injured in 20-30%; if high-velocity then 40%

8 hour window...

If dislocation is still present, joint injury is easy to diagnose

-Reduce if dislocated!

-Search for hard and soft vascular signs

-If hard vascular signs are present, popliteal artery injury is easy to diagnose

--Hard signs = Pulse deficits, ischemic limb, active hemorrhage, expanding/pulsatile hematoma

--Soft signs = Small/stable hematoma, injury to anatomically related nerve, history of hemorrhage

Considerations:-Knee may present already reduced

-Finding of significant ligament laxity

-NB: Rate of arterial injury is the SAME, regardless

-Knee swelling is NOT universal

--Knee capsule is frequently disrupted, allowing hemarthrosis to leak into surrounding tissues

-Normal pulses do NOT rule-out a vascular injury

--10% of vascular injuries have normal palpated pulses

-Xray

SOFT SIGNS

Requires further evaluation/studies

-ABI's

-Duplex Doppler Ultrasonography

--Reported sensitivity of 95% and specificity of 99%

--Can miss intimal tears (intimal tears > 30% ofvessel lumen are felt to be “significant”).

HARD SIGNS

OR +/- CT Angiogram prior

Reduction, ortho, vascular consult if necessary

Amputation rate:

>8h = 80%

<8h = 15%

Authors: