The patella

The patella bone lies within the substance of the tendon of the quadriceps muscle and is in contact with the femur bone behind it - this region is called the 'patello-femoral' joint. The back of the patella is covered with smooth, shiny white joint cartilage and is in contact with the cartilage of the femur within a groove known as the 'trochlear groove'. This contact area is important as small changes in contact forces may trigger pain in the knee.

The red circles in the next two images show two different views of the patellofemoral joint.

In the left of the two images one is looking at the bones from the front of the bent knee. In the right image one is looking at the straightened knee from the side.