A, Triangular arrangement of passive elements in posterior capsule of knee crucial for rotary stability. B, Posterior view of knee showing ligamentous reinforcement of posterior capsule. Oblique popliteal ligament is dynamically stabilized by semimembranosus muscle and arcuate ligament by popliteus muscle. AL, Arcuate ligament; AT, anterior tibial; Fa, fabella; LCL, lateral collateral ligament; LG, lateral gastrocnemius muscle; MCL, medial collateral ligament; MG, medial gastrocnemius muscle; OPL, oblique popliteal ligament; PL, plantaris longus muscle; Po, popliteus muscle; POL, posterior oblique collateral ligament; PT, popliteal tendon; Sm, semimembranosus.