3-D CT scan reconstruction of the right distal femur illustrating the femoral tunnel classification system for the anterior cruciate ligament (ACL). a. Distal view. b. Medial view. c. Posterior view. d. Posteromedial view. Type I tunnels (appropriately positioned or anatomical) are entirely contained within the green zone, located posterior and inferior to the lateral intercondylar ridge (black line). Type II tunnels (slightly malpositioned) partially overlap the lateral intercondylar ridge and extend into the orange zone. Type III tunnels (severely malpositioned or non-anatomical) are positioned completely anterior and superior to the lateral intercondylar ridge, extending into the red zone.