When a patient continues to dislocate their kneecap, or patella, it is often because the anatomy of their knee has a subtle, or not so subtle, alteration that allows the patella to dislocate more easily than normal. One of these anatomical differences can involve the groove (trochlea) on the front of the thigh bone (femur). The groove, or trochlea, usually has a depth to it making it harder for the patella to dislocate. Sometimes the trochlea is not as deep as normal - being shallow or flat or even convex. This is called trochlear dysplasia, essentially when the groove does not have its normal shape and may not be a groove at all.
If this problem is a major cause for a patella to continue to re-dislocate, a surgeon may propose surgery to change the shape of the trochlea . This is called a Trochleoplasty. This is a significant procedure where the shape of the joint surface of the groove is changed, with efforts to avoid damage to the surface while performing the surgery. The purpose is to create more of a groove than there was. It is combined with a Medial Patellofemoral Ligament (MPFL) Reconstruction. The Trochleoplasty tries to address the abnormal shape of the groove by deepening it while the MPFL Reconstruction re-builds the soft tissues that have been damaged by the repeat dislocations.