Traumatic patellar dislocations are considered to be a consequence of active lifestyle and defined as acute ligamentous knee injury. The management of a primary traumatic patellar dislocation has been controversial. The medial patellofemoral ligament (MPFL) has been recognized as the primary medial stabilizer of the patella. This thesis book investigates the incidence, risk factors initial management of primary traumatic patellar dislocation, the long-term results of MPFL reconstruction and the clinical significance of the MPFL injury in primary traumatic patellar dislocation. The results of the studies of this thesis disclosed that primary traumatic patellar dislocation is a common knee injury. To explore the clinical significance of the MPFL injury location, the magnetic resonance imaging evaluation proved that a femoral avulsion of the MPFL predicted subsequent instability and lower return to preinjury level of activity than other MPFL injury locations.