Transient lateral patellar dislocation: review of imaging findings, patellofemoral anatomy, and treatment options.

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 half of cases are unsuspected clinically. Characteristic magnetic resonance imaging (MRI) findings often lead to the diagnosis. The purpose of this review is to illustrate the MRI findings of lateral patellar dislocation and concomitant injuries, such as kissing contusions of the medial patella and lateral femoral condyle; osteochondral and avulsion fractures; and injuries of the medial patellofemoral ligament/retinacular complex. This article will also briefly review patellofemoral anatomy and passive, active, and static stabilizers. Predisposing factors for patellar instability, including trochlear dysplasia, patella alta, and lateralization of the patella or tibial tuberosity and their relevant measurements will also be highlighted. Treatment options, including surgery, such as medial patellofemoral ligament reconstruction, tibial tuberosity transfer, and trochleoplasty, and their postoperative imaging appearances will also be discussed.