Development and clinical application of kinematic MRI of the patellofemoral joint using an extremity MR system

Purpose: Kinematic magnetic resonance imaging (MRI) of the patellofemoral j oint provides diagnostic information pertaining to patellar alignment and t racking during the earliest increments of joint flexion, when abnormalities that affect this joint are: the most apparent. Recently, a low-field stren gth (0.2 Tesla) dedicated extremity AIR system has been designed, such that only the body part that is being imaged is placed inside of the magnet bor e. The purpose of this investigation was to develop a kinematic MRI techniq ue for the patellofemoral joint using the extremity MR system and to apply this procedure in the clinical setting. Methods: An incremental, passive po sitioning kinematic MRI technique was developed for the patellofemoral join t that involved obtaining three different axial section locations with the patellofemoral joint extended and then imaging these same section locations repeatedly as the patellofemoral joint was flexed in four increments up to 36 degrees of flexion. MR images were obtained using a T1-weighted spin ec ho sequence. Five (10 PFJ) asymptomatic volunteers and nine patient (9 PFJ) with patellofemoral joint symptoms were studied. Results: Volunteers had n ormal kinematic MRI examinations. Seven patients had lateral subluxation, a nd two patients had excessive lateral pressure syndrome. Two patients with lateral subluxation seen on their kinematic MRI studies had Merchant views (x-rays obtained at 45 degrees) that showed "normal" patellar alignment, il lustrating the importance of imaging the patellofemoral joint at 30 degrees or less. Conclusions: A kinematic MRI technique was successfully developed for the low-field extremity MR system and utilized for clinical applicatio ns. This procedure may be used to determine the presence anal severity of p atellar malalignment and abnormal tracking patterns.