Name of test

Posterior sag test of the knee

What it tests

Posterior cruciate ligament (PCL)

How to do it

The patient lies lies supine with the leg held by the examiner so that the hip and knee are flexed to 90 degrees. The main parameter in this test is step-off, which is the shortest distance from the femur to a hypothetical line that tangents the surface of the tibia from the tibial tuberosity and upwards.

The normal response

Normal step-off of approximately 1 cm

What it means if not normal

Decreased (Grade I), absent (Grade II), or inverse (Grade III) step-off suggests injury to the PCL



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