Articular cartilage deformation determined in an intact tibiofemoral joint by displacement-encoded imaging.

This study demonstrates the in vitro displacement and strain of articular cartilage in a cyclically-compressed and intact joint using displacement-encoded imaging with stimulated echoes (DENSE) and fast spin echo (FSE). Deformation and strain fields exhibited complex and heterogeneous patterns. The displace- ments in the loading direction ranged from 1688 to 1481 m in the tibial cartilage and from 1601 to 764 m in the femoral cartilage. Corresponding strains ranged from 9.8% to 0.7% and from 4.3% to 0.0%. The displacement and strain precision were determined to be 65 m and less than 0.2%, respectively. Displacement-encoded magnetic resonance imaging is capa- ble of determining the nonuniform displacements and strains in the articular cartilage of an intact joint to a high precision. Knowledge of these nonuniform strains is critical for the in situ characterization of normal and diseased tissue, as well as the comprehensive evaluation of repair constructs designed using regenerative medicine. Magn Reson Med 61:989 -993, 2009. The measurement of articular cartilage deformation pat- terns in the intact tibiofemoral joint in vitro can provide unique information regarding degenerative joint diseases. Comparison of deformations from degenerated and healthy knees may elucidate mechanisms of osteoarthritis progression. Knowledge of deformation patterns in whole joints in vitro would be advantageous in the design and evaluation of engineered or repaired cartilage (1,2) and in the development and validation of mathematical models of intact joints. Additionally, as a step toward in vivo measurements, the characterization of articular cartilage deformation in whole joints in vitro is necessary. MRI has the potential to noninvasively measure articu- lar cartilage deformation in an intact joint. MRI techniques to determine tissue displacement were initially developed to study myocardial deformation (3-5). Among MR studies of orthopedic tissue deformation, spoiled gradient recalled acquisition was used to measure change in cartilage con- tact area (6), and fast low-angle shots were used to com- pare cartilage thickness before and after compression (7- 9). These measures, however, are not indicative of the heterogeneous deformations occurring within the tissue of interest. Displacement-encoded imaging with stimulated echoes and fast spin echo readout were previously combined (DENSE-FSE) for measurement of heterogeneous displace- ments at a precision below the image spatial resolution in bovine articular cartilage explants (10). Although deforma- tion patterns were determined in explants, it is unclear whether patterns observed are meaningful in the context of joint loading, where multiple tissue contacts and complex geometry may result in unexpected deformations. There- fore, the present work extends the previous technique to compute displacement and strain patterns in the articular cartilage of a compressed and intact tibiofemoral joint. To this end, a loading apparatus was designed to cyclically compress an intact joint within an MRI scanner. The first objective was to evaluate the precision of the DENSE-FSE technique with an imaging phantom. A second objective was to demonstrate the in-plane deformation of articular cartilage in an intact tibiofemoral joint, which was ex- pected to be heterogeneous.