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 arthroscopic findings in cases of suspected femoropatellar malalignment. SUBJECTS AND METHODS. Twenty patients with clinically proved or suspected patellar subluxation or dislocation were examined prospectively with motion-triggered cine MR imaging to analyze patellar tracking from 30° of flexion to full extension during active extension of the knee. The patellar tracking pattern was evaluated by measuring the following: bisect offset and lateral patellar displacement to assess lateralization of the patella and the patellar tilt angle to assess tilting of the patella. The slopes of the linear regression lines of the MR findings vs the knee angle position, representing the patellar tracking, and the position of the patella at 30° and 0° of flexion were correlated with a semiquantitative arthroscopic classification of patellar tracking that had four categories ranging from normal to highly abnormal. RESULTS. The results showed a significant correlation between the semiquantitative arthroscopic findings of patellar tracking and the slopes of the linear regression lines of the bisect offset, lateral patellar displacement, and patellar tilt angle, as measured with cine MR imaging (p < .01). The arthroscopic finding also correlated significantly with the position of the patella when the knee was extended (p < .01), but not with the knee flexed 30°. CONCLUSION. We conclude that motion-triggered cine MR imaging of active extension of the knee enables the dynamic evaluation of patellar bracing and is therefore suitable for noninvasive analysis of patellar tracking.