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

ABSTRACT

PURPOSE: Kinematic magnetic resonance imaging (MRI) of the patellofemoral joint provides diagnostic information pertaining to patellar alignment and tracking during the earliest increments of joint flexion, when abnormalities that affect this joint are the most apparent. Recently, a low-field strength (0.2 Tesla) dedicated extremity MR system has been designed, such that only the body part that is being imaged is placed inside of the magnet bore. The purpose of this investigation was to develop a kinematic MRI technique for the patellofemoral joint using the extremity MR system and to apply this procedure in the clinical setting. METHODS: An incremental, passive positioning kinematic MRI technique was developed for the patellofemoral joint 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 echo sequence. Five (10 PFJ) asymptomatic volunteers and nine patients (9 PFJ) with patellofemoral joint symptoms were studied. RESULTS: Volunteers had normal kinematic MRI examinations. Seven patients had lateral subluxation, and 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, illustrating 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 applications. This procedure may be used to determine the presence and severity of patellar malalignment and abnormal tracking patterns.