Introduction

The knee joint consists of two main joints, the tibio-femoral and patello-femoral joints.  

An MRI scan showing a cross-section thro the knee at the leve of the Patello-femoral joint.

There is a third lesser important joint called the proximal tibiofibular joint which is a fibrous joint between the top of the shin bone and fibula.

The patella (kneecap) is a bone which is contained within the quadriceps tendon.   Bones contained within tendons are called sesamoids and the patella is the biggest sesamoid in the body. The function of the patella is to increase the lever-arm of the quadriceps mechanism, by moving it away from the trochlea grove. This increases the strength of the quadriceps. In people who have the patella removed surgically (patellectomy) for various reasons, the power of the quadriceps decreases by 30%, which is why patellectomy should be avoided.

The patella arbitrarily divides the quadriceps tendon into what is known as the patellar tendon below the patella and the quadriceps tendon above the patella. The patella moves against the trochlea groove at the end of the femur.   As the patella forms part of the joint it is also covered by articular cartilage.

The patello-femoral joint has to tolerate some of the largest body weight forces in the body and can have to withstand up to 8 to 9 times of body weight with activities such as jumping, running and stair climbing.   It is therefore not surprising that the patellar has the thickest articular cartilage of any joint in the body.

Patello-femoral disorders can be roughly broken down into:

• Patello-femoral pain
• Patello-femoral instability
• Patello-femoral pain and instability