Abstract
Degenerative changes of menisci contribute to the evolution of osteoarthritis in the knee joint, because they alter the load transmission to the adjacent articular cartilage. Identifying alterations in the strain response of meniscal tissue under compression that are associated with progressive degeneration may uncover links between biomechanical function and meniscal degeneration. Therefore, the goal of this study was to investigate how degeneration effects the three-dimensional (3D; axial, circumferential, radial) strain in different anatomical regions of human menisci (anterior and posterior root attachment; anterior and posterior horn; pars intermedia) under simulated compression. Magnetic resonance imaging (MRI) was performed to acquire image sequences of 12 mild and 12 severe degenerated knee joints under unloaded and loaded [25%, 50% and 100% body weight (BW)] conditions using a customized loading device. Medial and lateral menisci as well as their root attachments were manually segmented. Intensity-based rigid and non-rigid image registration were performed to obtain 3D deformation fields under the respective load levels. Finally, the 3D voxels were transformed into hexahedral finite-element models and direction-dependent local strain distributions were determined. The axial compressive strain in menisci and meniscal root attachments significantly increased on average from 3.1% in mild degenerated joints to 7.3% in severe degenerated knees at 100% BW (p ≤ 0.021). In severe degenerated knee joints, the menisci displayed a mean circumferential strain of 0.45% (mild: 0.35%) and a mean radial strain of 0.41% (mild: 0.37%) at a load level of 100% BW. No significant changes were observed in the circumferential or radial directions between mild and severe degenerated knee joints for all load levels (p > 0.05). In conclusion, high-resolution MRI was successfully combined with image registration to investigate spatial strain distributions of the meniscus and its attachments in response to compression. The results of the current study highlight that the compressive integrity of the meniscus decreases with progressing tissue degeneration, whereas the tensile properties are maintained.
Highlights
Osteoarthritis (OA) of the knee joint is one of the most widespread diseases and of great clinical and socioeconomic importance (Woolf and Pfleger, 2003; Altman, 2010)
The axial compressive strains in menisci and meniscal root attachments significantly increased by up to 135% in severe degenerated knee joints compared with mild degenerated knees for each anatomical region at 100% body weight (BW) (p ≤ 0.021, Figure 3A)
Investigating compressive strain under different load levels revealed significantly higher strains (p ≤ 0.002) in severe degenerated knee joints for all regions when the load was increased from 25% BW to 100% BW
Summary
Osteoarthritis (OA) of the knee joint is one of the most widespread diseases and of great clinical and socioeconomic importance (Woolf and Pfleger, 2003; Altman, 2010). The mechanical function of the meniscus depends on the structural and molecular integrity of its highly hydrated extracellular matrix, primarily composed of water (∼60–70%), collagen type I (∼15–25%) and a small amount of proteoglycans (PGs) (1– 2%) (Herwig et al, 1984; Fithian et al, 1990; Mow et al, 2005). Studies have shown that meniscal pathologies, including meniscal tears and degenerative changes of the extracellular matrix, contribute to OA evolution, because they alter the load transmission and distribution to the adjacent articular cartilage (Bolbos et al, 2009; Englund et al, 2011; Guermazi et al, 2013). Quantitative measurements to detect biomechanical changes in meniscal tissue response under loaded conditions are important for the understanding of meniscal physiology, but could provide a potential valuable diagnostic tool for early stage OA
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