The knee joint is a complex joint allowing bending, straightening and small amounts of rotator movements. It is a very unstable joint.
Bone
Femur, Tibia & Patella form the joint.
Cartilage
Apart from the normal joint cartilage, the knee is atabilized by a pair of additional cartilages called the meniscal cartilages (Medial Meniscus & Lateral Meniscus)
Ligaments
Stability is provided by 4 strong ligaments, 2 inside the joint (The Anterior Crutiate ligament & the Posterior Crutiate ligament ) and 2 outside the joint on either sides (Medial & Lateral Collateral ligaments)
Muscle Tendons
Joint is moved by the bulky quadriceps muscle in the front and the hamstring & gastromnemius muscles behind.