The Knee Joint

The knee joint is the largest joint in the human body, and the joint most commonly affected by arthritis. It is classified as a pivotal hinge joint, the knee allows for straightening and bending in one direction, with some twisting and minimal side-to-side motion. 
The bottom of the femur (thigh bone) meets with top of the tibia (shin bone), 
The patella (kneecap) glides along a grove located at the bottom and front of the femur . Within the knee articular cartilage covers the surfaces of the bones where they meet: at the bottom of the femur, the top of the tibia, and the back of the kneecap. The cartilage allow the bones to glide smoothly and also acts as a shock absorber . Between the tibia and the femur are two thick pads called the menisci. The menisci reduce shock and absorb impact when the knee is moving or bearing weight. They also help stabilise the knee and facilitate smooth motion between the surfaces of the knee. The tibia and the femur are connected to each other by 2 strong bands of tissue called the  anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). They prevent the tibia  from slipping forward and backwards, they also limit rotation . There is another set of ligaments called the collateral ligaments, they minimise side to side movements. A delicate, thin membrane, called the synovial membrane, encapsulates the knee joint. The synovial membrane produces synovial fluid. This viscous fluid lubricates and circulates nutrients to the joint.The knee cap is secured in place in front of the knee by the quadriceps muscle and the patella tendon. There are multiple other muscles encapsulating the knee and contribute to the stability and movement .