Mechanisms of energy dissipation and relationship with tissue composition in human meniscus

Abstract

Objective: The human meniscus is essential in maintaining proper knee joint function. The meniscus absorbs shock, distributes loads, and stabilizes the knee joint to prevent the onset of osteoarthritis. The extent of its shock-absorbing role can be estimated by measuring the energy dissipated by the meniscus during cyclic mechanical loading.

Methods: Samples were prepared from the central and horn regions of medial and lateral human menisci from 8 donors (both knees for total of 16 samples). Cyclic compression tests at several compression strains and frequencies yielded the energy dissipated per tissue volume. A GEE regression model was used to investigate the effects of compression, meniscal side and region, and water content on energy dissipation in order to account for repeated measures within samples.

Results: Energy dissipation by the meniscus increased with compressive strain from ∼0.1 kJ/m³ (at 10% strain) to ∼10 kJ/m³ (at 20% strain) and decreased with loading frequency. Samples from the anterior region provided the largest energy dissipation when compared to central and posterior samples (P < 0.05). Water content for the 16 meniscal tissues was 77.9 (C.I. 72.0-83.8%) of the total tissue mass. A negative correlation was found between energy dissipation and water content (P < 0.05).

Conclusion: The extent of energy dissipated by the meniscus is inversely related to loading frequency and meniscal water content.

Keywords: Cyclic compression; Hysteresis; Meniscal dampening; Water content.

Figure A1:

Energy dissipation vs. compression frequency. Data are segregated by magnitude of compression (10%: a-c, 15%: d-f, 20%: g-i) and regions (anterior: a, d, g; central: b, e, h; posterior: c, f, i). Open circles refer to lateral samples and closed circles to medial ones.

Figure A2:

Energy dissipation vs. water content: (a) 10% compression magnitude; (b) 15% compression magnitude; (c) 20% compression magnitude. Open symbols refer to lateral samples and closed symbols to medial ones. Triangles, circles and squares represent the anterior regions, the central regions and posterior regions, respectively. The colors of the symbols refer to the frequencies of compression: 0.125 Hz (black), 0.25 Hz (red), and 0.5 Hz (blue).

Figure 1:

Experimental procedures: a) samples were obtained from the posterior, central and anterior regions of human menisci; b) meniscal wedges were cut into 1.5 mm slices with Compresstome®; c) a 5mm corneal trephine was used to core the slices into discs; d) representative meniscus sample used in compression experiments; e) customized compression chamber for unconfined compression; f) compression cycles consisted of a series of trapezoidal loading curve with a 600s rest time between each cycle.

Figure 2:

Representative force response during a cycle of 20% compression strain at a frequency of 0.125 Hz. The equilibrium force recovers to pre-compression levels within the allotted 600s rest time.

Figure 3:

GEE regression model coefficients of energy dissipation comparisons across compression levels, compression frequencies, meniscal side, and meniscal regions. All comparisons were conducted with respect to the case of 10% compression strain, 0.125 Hz compression frequency, lateral side, and anterior region. Bars in the diagram represent the 95% confidence interval of the coefficient.

Figure 4:

GEE regression model coefficients of energy dissipation association with water content for all meniscal sides and regions. Bars in the diagram represent the 95% confidence interval of the coefficient.