SHEEHAN, F. T. and J. E. DRACE. Quantitative MR measures of three-dimensional patellar kinematics as a research and diagnostic tool.Med. Sci. Sports Exerc.,Vol. 31, No. 10, pp. 1399–1405, 1999.Purpose:A three-dimensional (3D) study of normal patellar-femoral-tibial (knee) joint kinematics was performed using Cine Phase Contrast Magnetic resonance imaging (Cine-PC MRI) to determine the utility of this technique as a diagnostic tool in defining alterations in patellar tracking.Methods:Cine-PC MRI was originally developed to measure heart motion and blood flow and has now been adapted to the study of the musculoskeletal system. Thus, for the first time knee joint kinematics can be studied three-dimensionally, noninvasively, andin vivoduring dynamic volitional leg extensions under load. Cine-PC MRI provides one anatomic and three orthogonal velocity images (vx, vy, and vz) 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 though these two angles have distinct mathematical definitions. The precision of the 2D clinical patellar tilt angle (N= 3) was approximately 2.4°.Conclusions:Since the overall subject (N= 18) variability for clinical patellar tilt angle and medial/lateral patellar displacement was low (SD = 2.9° and 3.3 mm, respectively), Cine-PC MRI could prove to be a valuable tool in studying subtle changes in patellar tracking.