In vivo patellofemoral contact mechanics during active extension using a novel dynamic MRI-based methodology.

OBJECTIVES: To establish an in vivo, normative patellofemoral (PF) cartilage contact mechanics database acquired during voluntary muscle control using a novel, dynamic, magnetic resonance (MR) imaging-based, computational methodology and validate the contact mechanics sensitivity to the known sub-millimeter methodological accuracies. DESIGN: Dynamic cine phase-contrast and multi-plane cine (MPC) images were acquired while female subjects (n = 20, sample of convenience) performed an open kinetic chain (knee flexion-extension) exercise inside a 3-T MR scanner. Static cartilage models were created from high resolution three-dimensional static MR data and accurately placed in their dynamic pose at each time frame based on the cine-PC (CPC) data. Cartilage contact parameters were calculated based on the surface overlap. Statistical analysis was performed using paired t-test and a one-sample repeated measures ANOVA. The sensitivity of the contact parameters to the known errors in the PF kinematics was determined. RESULTS: Peak mean PF contact area was 228.7 ± 173.6 mm(2) at 40° knee angle. During extension, contact centroid and peak strain locations tracked medially on the femoral and patellar cartilage and were not significantly different from each other. At 25°, 30°, 35°, and 40° of knee extension, contact area was significantly different. Contact area and centroid locations were insensitive to rotational and translational perturbations. CONCLUSION: This study is a first step towards unfolding the biomechanical pathways to anterior PF pain and osteoarthritis (OA) using dynamic, in vivo, and accurate methodologies. The database provides crucial data for future studies and for validation of, or as an input to, computational models.

Human patellar tendon strain. A noninvasive, in vivo study.

This study showed the assumption of patellar tendon inextensibility was not valid, and the strain in the patellar tendon was higher than previously reported for other human tendons. The in vivo three-dimensional velocity profiles for the patella, femur, and tibia were measured noninvasively in 18 healthy knees during a low load extensor task using cine phase contrast magnetic resonance imaging. These data were used to calculate patellar tendon elongation and strain. Average maximum strains of 6.6% were found for a low load extension task at relatively small knee angles.

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 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, and in vivo during 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 degrees. CONCLUSIONS: Since the overall subject (N = 18) variability for clinical patellar 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 valuable tool in studying subtle changes in patellar tracking.

In vivo tracking of the human patella using cine phase contrast magnetic resonance imaging.

Improper patellar tracking is often considered to be the cause of patellar-femoral pain. Unfortunately, our knowledge of patellar-femoral-tibial (knee) joint kinematics is severely limited due to a lack of three-dimensional, noninvasive, in vivo measurement techniques. This study presents the first large-scale, dynamic, three-dimensional, noninvasive, in vivo study of nonimpaired knee joint kinematics during volitional leg extensions. Cine-phase contrast magnetic resonance imaging was used to measure the velocity profiles of the patella, femur, and tibia in 18 unimpaired knees during leg extensions, resisted by a 34 N weight. Bone displacements were calculated through integration and then converted into three-dimensional orientation angles. We found that the patella displaced laterally, superiorly, and anteriorly as the knee extended. Further, patellar flexion lagged knee flexion, patellar tilt was variable, and patellar rotation was fairly constant throughout extension.

Using cine phase contrast magnetic resonance imaging to non-invasively study in vivo knee dynamics.

We tested the accuracy and feasibility of using cine phase contrast magnetic resonance imaging (cine-PC MRI) to non-invasively measure three-dimensional, in vivo, skeletal velocity. Bone displacement was estimated by integrating the velocity measurements. Cine-PC MRI was originally developed to directly and non-invasively measure in vivo blood and heart velocity. Since no standard of reference exists for in vivo measurement of trabecular bone motion, a motion phantom (consisting of a series of paired gears that moved a sample box containing a human femoral bone sample) was built to assess the accuracy of tracking trabecular bone with cine-PC MRI. The in-plane, average absolute displacement errors were 0.55 +/- 0.38 and 0.36 +/- 0.27 mm in the x- and y-direction, respectively. Thus, estimates of bone position based on the integration of bone velocity measurements are affected little by the magnetic properties of bone [Majumdar and Genant (1995) Osteoporos International 5, 79-92]. The velocity profiles of the patella, femur and tibia were measured in five healthy subjects during leg extensions. Extension was resisted by a 34 N weight. Subjects maintained a consistent motion rate (35 +/- 0.5 cycles min(-1)) and motion artifacts were minimal. Our results indicate that patellar flexion lags knee flexion and the patella tilts laterally and then medially as the knee extends. We conclude cine-PC MRI is a promising technique for the non-invasive measurement of in vivo skeletal dynamics and, based on our previous work, muscular dynamics as well.