Magnetic resonance imaging analysis of rotational alignment in pediatric patients with patellar dislocations

The cause of patellofemoral instability is not completely understood and appears to be multifactorial, resulting from abnormalities in the patellar stabilizers. Established primary anatomic risk factors include trochlear dysplasia, high patella, and lateralized patellar tendon attachment. Most patients with a dislocation have anatomic risk factors, which vary in severity and constellation. The evaluation of these anatomical variants with magnetic resonance imaging (MRI) is simple, and the avoidance of radiation makes it preferable to computed tomography. It is performed using T1-weighted and DP sequences to measure femoral anteversion, distance from the intercondylar groove to the anterior tibial tuberosity, trochlear angle and external tibial torsion to determine rotational alignment of the limbs; abnormal values suggest patellofemoral instability. These patients require a preoperative diagnostic MRI study for quantitative assessment of secondary damage (e.g., location of medial patellofemoral ligament rupture, osteochondral fractures) and underlying risk factors.