Most dislocations of the patella occur during sports activities. The entities instability, maltracking and loss of tracking should be defined by patient history, clinical examination and radiological evaluation including magnetic resonance imaging (MRI). Based on these criteria a new classification of patella dislocations (5 types) was established which allows a standardized treatment algorithm. Type 1 is a simple (traumatic) dislocation without maltracking and without instability. Type 2 has a high redislocation risk (defined as instability) without maltracking. An isolated stabilizing surgical procedure, such as medial patellofemoral ligament (MPFL) augmentation is successful in most cases. Type 3 is characterized by instability and maltracking. Maltracking can be caused by soft tissue contracture or muscular deficits (type 3a), patella alta (type 3b), pathological tibial tuberosity to trochlear groove (TT-TG) distance (type 3c), genu valgum (type 3d) and torsional deformities (type 3e). In these types an isolated soft tissue procedure is usually not sufficient. The bony pathologies additionally need to be addressed to regain physiological patella tracking. Type 4 includes severe trochlea dysplasia with loss of patella tracking. Usually trochleaplasty is needed to stabilize the patella and to prevent redislocation. Type 5 is based on patella maltracking without instability and can be found in patients with a pathological knee baseline or special forms of torsional deformities. Although patella dislocations in trained athletes are seldom due to the stabilizing muscular status, the treatment strategy is similar to that of normal persons. Additional cartilage injuries, type of sports and time for rehabilitation have to be considered for optimal treatment.
