Posterior sag sign (Godfrey's sign)

With the knee flexed to 80 degrees examine the prominence of the proximal tibia relative to the femoral condyles. Normally in this position a straight line passing up the tibia over the tibial tuberosity will pass well in front of the patella. In a PCL deficient knee, the knee be posteriorly subluxed due to gravity and the tibial tuberosity does not have it's normal prominence.

Suspending the leg by the heel and holding the knee at 90 degrees will demonstrate even subtle differences between the side - due to partial PCL rupture. (this photo shows a pair of normal knees!)

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