EVALUATION OF PATELLAR TRACKING IN PATIENTS WITH SUSPECTED PATELLAR MALALIGNMENT - CINE MR-IMAGING VS ARTHROSCOPY

OBJECTIVE. The purpose of this study was to compare results of motion- triggered cine MR imaging of active extension of the knee with arthros copic findings in cases of suspected femoropatellar malalignment. SUBJ ECTS AND METHODS. Twenty patients with clinically proved or suspected patellar subluxation or dislocation were examined prospectively with m otion-triggered cine MR imaging to analyze patellar tracking from 30 d egrees of flexion to full extension during active extension of the kne e. The patellar tracking pattern was evaluated by measuring the follow ing: bisect offset and lateral patellar displacement to assess lateral ization of the patella and the patellar tilt angle to assess tilting o f the patella. The slopes of the linear regression lines of the MR fin dings vs the knee angle position, representing the patellar tracking, and the position of the patella at 30 degrees and 0 degrees of flexion were correlated with a semiquantitative arthroscopic classification o f patellar tracking that had four categories ranging from normal to hi ghly abnormal. RESULTS. The results showed a significant correlation b etween the semiquantitative arthroscopic findings of patellar tracking and the slopes of the linear regression lines of the bisect offset, l ateral patellar displacement, and patellar tilt angle, as measured wit h cine MR imaging (p <.01). The arthroscopic findings also correlated significantly with the position of the patella when the knee was exten ded (p <.01), but not with the knee flexed 30 degrees. CONCLUSION. We conclude that motion-triggered cine MR imaging of active extension of the knee enables the dynamic evaluation of patellar bracing and is the refore suitable for noninvasive analysis of patellar tracking.