This is a clinical test used to assess the anterior cruciate ligament (ACL). The patient lays on their back on the exam table.  The examiner places one hand behind the knee on the lower leg bone, and uses the other hand to grasp the thigh just above the knee.  The patient is asked to relax.  The examiner then attempts to slide the lower leg forward under the thigh bone (which he is holding still).  If the ACL is intact, the examiner should feel a firm stopping point – like he is tugging on a rope.  If there is no firm endpoint, the test is “positive” and suggestive of a torn ACL tendon.