Transient patellar dislocation is a common sports-related injury in young adults. Although patients often present to the emergency department with acute knee pain and hemarthrosis, spontaneous reduction frequently occurs, and more than half of cases are assessed clinically with spontaneous reduction. Characteristic magnetic resonance imaging (MRI) findings often confirm the diagnosis and illustrate the underlying etiology.
It is unusual for the patella to dislocate from trauma alone in a patient without predisposing factors for instability. The most common factors are trochlear dysplasia, patella alta, and lateralization of the tibial tuberosity.
Structural changes associated with patellar mal-tracking include; injuries to the medial patellar stabilizers, superolateral Hoffa's fat pad impingement and chondral and osteochondral injuries.

AIM OF THE WORK
The aim of this study was to determine the role of MRI in patellofemoral instability.


SUBJECTS AND METHODS
Target population:
This was a case-control study that included 37 patients (34 of them had unilateral PFI and 3 patients had bilateral PFI) attending the orthopedic Unit at Alexandria University Hospitals with a history of patella-femoral instability in the form of transient patellar dislocation and 40 controls. A total of 80 knees were examined, 40 knees showed features of PFI and were considered as the case group, while 40 normal knees of age and sex-matched people were considered as the control group.