Mechanical and Microstructural Properties of Meniscus Roots Vary by Location

Abstract

Background: Despite the growing awareness of the clinical significance of meniscus root tears, there are relatively limited biomechanical and microstructural data available on native meniscus roots that could improve our understanding of why they are injured and how to best treat them. Purpose/Hypothesis: The purpose of the study was to measure the material and microstructural properties of meniscus roots using mechanical testing and quantitative polarized light imaging. The hypothesis was that these properties vary by location (medial vs lateral, anterior vs posterior) and by specific root (anteromedial vs anterolateral, posteromedial vs posterolateral). Study Design: Descriptive laboratory study. Methods: Anterior and posterior meniscus roots of the medial and lateral meniscus were isolated from 22 cadavers (10 female, 12 male; mean ± SD age, 47.1 ± 5.1 years) and loaded in uniaxial tension. Quantitative polarized light imaging was used to measure collagen fiber organization and realignment under load. Samples were subjected to preconditioning, stress-relaxation, and a ramp to failure. Time-dependent relaxation behavior was quantified. Modulus values were computed in the toe and linear regions of the stress-strain curves. The degree of linear polarization (DoLP) and angle of polarization—measures of the strength and direction of collagen alignment, respectively—were calculated during the stress-relaxation test and at specific strain values throughout the ramp to failure (zero, transition, and linear strain). Results: Anterior roots had larger moduli than posterior roots in the toe ( P = .007) and linear ( P < .0001) regions and larger average DoLP values at all points of the ramp to failure (zero, P = .016; transition, P = .004; linear, P = .002). Posterior roots had larger values across all regions in terms of standard deviation angle of polarization ( P < .001). Lateral roots had greater modulus values versus medial roots in the toe ( P = .027) and linear ( P = .014) regions. Across all strain points, posterolateral roots had smaller mean DoLP values than posteromedial roots. Conclusion: Posterior meniscus roots have smaller modulus values and more disorganized collagen alignment at all strain levels when compared with anterior roots. Posterolateral roots have lower strength of collagen alignment versus posteromedial roots. Clinical Relevance: These data findings may explain at least in part the relative paucity of anterior meniscus root tears and the predominance of traumatic posterolateral roots tears as compared with degenerative posteromedial root tears.