The patellofemoral joint is a very complex joint consisting of two bones at the front of the knee. The two bones are the patella (kneecap) and the front of the distal femur (thigh bone just deep to the kneecap.)

The patella joins with the front of the femur in the area called the trochlea. This joint is made up of complex interplay of muscles, tendons, ligaments and boney anatomy. Problems with any of these can cause pain and instability around the patellofemoral joint.

What is Patellofemoral instability / dislocation?

Patellofemoral instability is a debilitating condition and can affect anybody at any age.

It is a tracking malfunction where the knee cap either feels like it wants to jump out to the side (instability) when bending the knee or actually DOES dislocate out to the side (dislocation). It is a truly debilitating condition and can stop sufferers from performing activities such as sport and sometimes even simple movements such as walking. 

The two most common presentations are teenage girls, who have developmental instability around the joint, or adult male and female athletes who have injuries to their knees resulting in instability.

What are the causes of Patellofemoral instability / dislocation?

Instability can be differentiated into developmental or traumatic causes. This means that if it's due to developmental causes then it is usually an abnormality with the joint. These can be due to:

  • a shallow trochlea (Trochlear dysplasia)
  • High riding patella (Patella Alta)
  • an abnormal insertion of the patellar tendon on the tibia (shin)
  • knock knees

If it's traumatic it means the anatomy may be fine but due to the trauma, there has been some damage caused to the joint - usually a rupture to the MPFL (medial patella-femoral ligament).

How is Patellofemoral instability / dislocation investigated?

We will carry out a thorough examination of the knee joint and we routinely carry out MRI scans to look at the anatomy in more detail to help work out what type of treatment may be required.