Abstract
The in vivo measurement of articular cartilage deformation is essential to understand how mechanical forces distribute throughout the healthy tissue and change over time in the pathologic joint. Displacements or strain may serve as a functional imaging biomarker for healthy, diseased, and repaired tissues, but unfortunately intratissue cartilage deformation in vivo is largely unknown. Here, we directly quantified for the first time deformation patterns through the thickness of tibiofemoral articular cartilage in healthy human volunteers. Magnetic resonance imaging acquisitions were synchronized with physiologically relevant compressive loading and used to visualize and measure regional displacement and strain of tibiofemoral articular cartilage in a sagittal plane. We found that compression (of 1/2 body weight) applied at the foot produced a sliding, rigid-body displacement at the tibiofemoral cartilage interface, that loading generated subject- and gender-specific and regionally complex patterns of intratissue strains, and that dominant cartilage strains (approaching 12%) were in shear. Maximum principle and shear strain measures in the tibia were correlated with body mass index. Our MRI-based approach may accelerate the development of regenerative therapies for diseased or damaged cartilage, which is currently limited by the lack of reliable in vivo methods for noninvasive assessment of functional changes following treatment.
Highlights
Telemetric joint implants[10,11], internal tissue deformations are challenging to visualize due to a number of inherent obstacles
The hierarchical anatomy of most orthopaedic tissues[12] means that, for a comprehensive understanding of the mechanics, tissue behavior should be examined at several length scales, either through direct measurement or mathematical modeling based on direct measurements
For tissue-level studies, joints can be imaged in vivo for tissue morphology, using magnetic resonance imaging (MRI) or other high-resolution techniques, and kinematic data for joint segments can be assessed via videographic, fluoroscopic, or MRI-based motion analysis[9,13,14]
Summary
Telemetric joint implants[10,11], internal tissue deformations are challenging to visualize due to a number of inherent obstacles. Techniques that estimate deformation fields during static load using texture correlation[29] or measure pixel displacements during low frequency loading using displacement-encoded MRI30 can directly measure in situ tissue strains on a clinical MRI system. These approaches show promise for the measurement of in vivo biomechanical behavior. We further hypothesized that male and female subjects would exhibit similar patterns and magnitudes of cartilage strain To address these hypotheses, synchronization of displacement-encoded MRI to cyclical loading of the leg, generated by an MRI-compatible loading device, enabled the visualization of soft tissue motion and contact. Characterization of in vivo mechanics in tibiofemoral cartilage as a model system demonstrates the utility and broad applicability of dualMRI for the study of mechanical behavior in a range of orthopaedic soft tissues
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