This is a clinical test for laxity of the anterior cruciate ligament.
The patient lies on his/her back on the examination couch. The examiner stands alongside the knee, facing the patient, and gently takes the knee into both hands, with the upper hand holding the thigh firmly just above the knee, and the lower hand holding the lower leg firmly with the fingers behind the leg and the thumb on the tibial tuberosity (the bony lump just below the kneecap).
The knee is bent to 20-30 degrees.
The lower leg is pulled forwards while the thigh is held firmly in position, and the examiner feels for any forward movement of the lower leg.