Quantitative MR measures of three-dimensional patellar kinematics as a research and diagnostic tool

Purpose: A three-dimensional (3D) study of normal patellar-femoral-tibial ( knee) joint kinematics was performed using Cine Phase Contrast Magnetic res onance imaging (Cine-PC MRI) to determine the utility of this technique as a diagnostic tool in defining alterations in patellar tracking. Methods: Ci ne-PC MRI was originally developed to measure heart motion and blood flow a nd has now been adapted to the study of the musculoskeletal system. Thus, f or the first time knee joint kinematics can be studied three-dimensionally, noninvasively, and in vivo during dynamic volitional leg extensions under load. Cine-PC MRI provides one anatomic and three orthogonal velocity image s (v(x), v(y), and v(z)) for each time frame within the motion cycle. Bone displacements are calculated using integration and are then converted into both 3D orientation angles and 2D clinical angles. Results: The 3D patellar tilt and 2D clinical patellar tilt angle were nearly identical, even thoug h these two angles have distinct mathematical definitions. The precision of the 2D clinical patellar tilt angle (N = 3) was approximately 2.4 degrees. Conclusions: Since the overall subject (N = 18) variability for clinical p atellar tilt angle and medial/lateral patellar displacement was low (SD = 2 .9 degrees and 3.3 mm, respectively), Cine-PC MRI could prove to be a valua ble tool in studying subtle changes in patellar tracking.