The knee joint is complex and maintains congruency in six degrees of freedom motion thanks to the ligamentous, capsular, and tendinous insertions that in combination with the periarticular muscles provide dynamic joint stability and proprioception not only activities of daily life but also in sports. The concept of quadrants and their stabilizers, the triangular stabilizing structures, are explained. The structures of the lateral side, also called the popliteus corner due to its stabilizing importance, are thoroughly described and analyzed. They are the iliotibial tract that includes the anterolateral ligament, the fibular collateral ligament-bíceps tendon complex, the popliteus tendon with its femoral, fibular, and meniscocapsular insertions, and the lateral gastrocnemius and the proximal tibiofibular joint.