Abstract
Introduction
With processing age, meniscus degeneration occurs which is often associated with osteoarthritis. Existing data about the influence of degeneration on the biomechanical properties of the meniscus are still contradictory, or completely unknown regarding the hydraulic permeability. Thus, the aim of this study was to characterise the biomechanical properties and structural composition of the meniscal tissue depending on its degree of degeneration.
Methods
Menisci of 24 TKR-patients (≈67.1 yrs.) were harvested and the degeneration of each region (pars anterior PA, pars intermedia PI, pars posterior PP) classified according to Pauli et al. For biomechanical characterisation, confined compression tests (20% strain; velocity: 3%h0/min, relaxation time: 1h) to determine equilibrium modulus (HA) and hydraulic permeability (k) and tensile tests (velocity: 5%l0/min) to determine the tensile modulus were performed. Therefore, cylindrical (Ø= 4.6mm, initial height h0≈ 2.3mm) and dumbbell-shaped (3.5mm × 1.4mm × 3.5mm) samples were punched out of each region and flattened to achieve parallel surfaces. Additionally, collagen and proteoglycan (PG) content were analysed by calculating the area-under-curve of their specific wavelength ranges (1293–1356cm−1 and 980–1120cm−1, respectively) using infrared (IR) spectroscopy. To identify differences regarding the meniscus regions or its degeneration, a statistically mixed model was used.
Results
The compression test showed a significant decrease in HA with increasing degeneration (from 78kPa to 55kPa) and from anterior to posterior region (PA: ≈90kPa to PP: ≈70kPa), whereas the hydraulic permeability increased significantly from ≈(1.4 to 3.1)*10−14m4N−1s−1 and ≈(1.5 to 3)*10−14m4N−1s−1, respectively. However, the tensile modulus was constant for all regions but showed a decreasing tendency with rising degeneration from ≈(48 to 28)MPa. The collagen content showed a significant decrease with increasing degeneration. The PG content revealed no significant differences regarding the sampling region but a downwards trend with increasing degeneration.
Discussion
For the first time, we were able to show a significant increase in the hydraulic permeability with progressive meniscus degeneration while decreasing aggregate modulus. Furthermore, according to a simultaneous downwards tendency in tensile modulus, the collagen content decreased significantly with increasing degeneration. These alterations in biomechanical properties in degenerative meniscal tissue are likely related to an increased water content, also shown e.g. by Pauli et al. In conclusion, our findings may contribute to the understanding of meniscus degeneration and how alterations of meniscal properties might influence the formation of osteoarthritis.
