Gross anatomical dissection of the popliteus muscle, the popliteus tendon and its fascicles, and their relation to the lateral meniscus was carried out in 14 human adult cadaver knees. Videoarthroscopy through an anterolateral portal was then used to assess and document the functional integrity of the popliteus tendon and its fascicles forming the popliteal hiatus in vivo. A control group of cruciate ligament intact knees (n = 107) was compared with an anterior cruciate ligament (ACL)-deficient group (n = 68). The incidence of structural lesions of the popliteus system was 18.7% in the control knees, 95% in 40 acute ACL disruptions, and 85.7% in 28 chronic ACL-deficient knees. Functional arthroscopic evaluation of the popliteus tendon and its fascicles blending into the lateral meniscus was a valuable adjunct in assessing secondary posterolateral restraints in acute and chronic ACL-incompetent knees.