Patellofemoral instability – in some patients the patella (kneecap) moves out of its normal position. If the patella moves partially out of the trochlear  groove, it is referred to as subluxation. Complete movement out of the groove is known as dislocation.  

Patellofemoral instability can be caused by a number of factors such as loss of articular cartilage from the back of the patella, abnormal shape of the patella and improper muscle balance (if the quadriceps muscle is weak this can lead to abnormal tracking of the patella). 

Treatment Options