Juuso T. J. Honkanen

Characterization of site-specific biomechanical properties of human meniscus—Importance of collagen and fluid on mechanical nonlinearities

Meniscus adapts to joint loads by depth- and site-specific variations in its composition and structure. However, site-specific mechanical characteristics of intact meniscus under compression are poorly known. In particular, mechanical nonlinearities caused by different meniscal constituents (collagen and fluid) are not known. In the current study, in situ indentation testing was conducted to determine site-specific elastic, viscoelastic and poroelastic properties of intact human menisci. Lateral and medial menisci (n=26) were harvested from the left knee joint of 13 human cadavers. Indentation tests, using stress-relaxation and dynamic (sinusoidal) loading protocols, were conducted for menisci at different sites (anterior, middle, posterior, n=78). Sample- and site-specific axisymmetric finite element models with fibril-reinforced poroelastic properties were fitted to the corresponding stress-relaxation curves to determine the mechanical parameters. Elastic moduli, especially the instantaneous and dynamic moduli, showed site-specific variation only in the medial meniscus (p<0.05 between the sites). The instantaneous and dynamic elastic moduli of the anterior horn were significantly (p<0.05) greater in the medial than lateral meniscus. The phase angle showed no statistically significant variation between the sites (p>0.05). The values for the strain-dependent fibril network modulus (nonlinear behaviour of collagen) were significantly different (p<0.05) between all sites in the medial menisci. Additionally, there was a significant difference (p<0.01) in the strain-dependent fibril network modulus between the lateral and medial anterior horns. The initial permeability was significantly different (p<0.05) in the medial meniscus only between the middle and posterior sites. For the strain-dependent permeability coefficient, only anterior and middle sites showed a significant difference (p<0.05) in the medial meniscus. This parameter demonstrated a significant difference (p<0.05) between lateral and medial menisci at the anterior horns. Our results reveal that under in situ indentation loading, medial meniscus shows more site-dependent variation in the mechanical properties as compared to lateral meniscus. In particular, anterior horn of medial meniscus was the stiffest and showed the most nonlinear mechanical behaviour. The nonlinearity was related to both collagen fibrils and fluid.

Comparison of nonlinear mechanical properties of bovine articular cartilage and meniscus

Nonlinear, linear and failure properties of articular cartilage and meniscus in opposing contact surfaces are poorly known in tension. Relationships between the tensile properties of articular cartilage and meniscus in contact with each other within knee joints are also not known. In the present study, rectangular samples were prepared from the superficial lateral femoral condyle cartilage and lateral meniscus of bovine knee joints. Tensile tests were carried out with a loading rate of 5mm/min until the tissue rupture. Nonlinear properties of the toe region, linear properties in larger strains, and failure properties of both tissues were analysed. The strain-dependent tensile modulus of the toe region, Youngs modulus of the linear region, ultimate tensile stress and toughness were on average 98.2, 8.3, 4.0 and 1.9 times greater (p<0.05) for meniscus than for articular cartilage. In contrast, the toe region strain, yield strain and failure strain were on average 9.4, 3.1 and 2.3 times greater (p<0.05) for cartilage than for meniscus. There was a significant negative correlation between the strain-dependent tensile moduli of meniscus and articular cartilage samples within the same joints (r=-0.690, p=0.014). In conclusion, the meniscus possesses higher nonlinear and linear elastic stiffness and energy absorption capability before rupture than contacting articular cartilage, while cartilage has longer nonlinear region and can withstand greater strains before failure. These findings point out different load carrying demands that both articular cartilage and meniscus have to fulfil during normal physiological loading activities of knee joints.

Contrast enhanced imaging of human meniscus using cone beam CT

OBJECTIVE Meniscal injuries can lead to mechanical overloading of articular cartilage and eventually to knee osteoarthritis. The objective was to evaluate the potential of contrast enhanced computed tomography (CECT) to image contrast agent (CA) diffusion in human menisci with a clinical cone beam CT scanner. DESIGN Isolated human menisci (n = 26) were imaged using magnetic resonance imaging (MRI) and CECT in situ. Diffusion of anionic CA into the meniscus was imaged for up to 30 h. The results of CECT were compared with water, collagen and proteoglycan (PG) contents, biomechanical properties, age and histological and MR images of the samples. RESULTS Diffusion of CA required over 25 h to reach equilibrium. The CA partition (the CA concentration in the tissue divided by that in the bath) at the 40 min time point correlated significantly with that at the 30 h time point in both lateral (r = 0.706, P = 0.007) and medial (r = 0.669, P = 0.012) menisci. Furthermore, CA partition in meniscus after 30 h of diffusion agreed qualitatively with the distribution of PGs. CONCLUSION The cross-sectional distribution of CA was consistent with that reported in a previous μCT study on bovine meniscus. The time required to reach diffusion equilibrium was found impractical for clinical applications. However, based on the present results, shorter delay between injection and imaging (e.g., 40 min) could be feasible in clinical diagnostics of meniscal pathologies.

Contrast-Enhanced Computed Tomography Enables Quantitative Evaluation of Tissue Properties at Intrajoint Regions in Cadaveric Knee Cartilage:

Objective The aim of this study was to investigate whether the concentration of the anionic contrast agent ioxaglate, as quantitated by contrast-enhanced computed tomography (CECT) using a clinical cone-beam CT (CBCT) instrument, reflects biochemical, histological, and biomechanical characteristics of articular cartilage imaged in an ex vivo, intact human knee joint. Design An osteoarthritic human cadaveric knee joint (91 years old) was injected with ioxaglate (36 mg I/mL) and imaged using CBCT over 61 hours of ioxaglate diffusion into cartilage. Following imaging, the joint surfaces were excised, rinsed to remove contrast agent, and compressive stiffness (equilibrium and instantaneous compressive moduli) was measured via indentation testing (n = 17 sites). Each site was sectioned for histology and assessed for glycosaminoglycan content using digital densitometry of Safranin-O stained sections, Fourier transform infrared spectroscopy for collagen content, and morphology using both the Mankin and OARSI semiquantitative scoring systems. Water content was determined using mass change after lyophilization. Results CECT attenuation at all imaging time points, including those <1 hour of ioxaglate exposure, correlated significantly (P < 0.05) with cartilage water and glycosaminoglycan contents, Mankin score, and both equilibrium and instantaneous compressive moduli. Early time points (<30 minutes) also correlated (P < 0.05) with collagen content and OARSI score. Differences in cartilage quality between intrajoint regions were distinguishable at diffusion equilibrium and after brief ioxaglate exposure. Conclusions CECT with ioxaglate affords biochemical and biomechanical measurements of cartilage health and performance even after short, clinically relevant exposure times, and may be useful in the clinic as a means for detecting early signs of cartilage pathology.

Optical spectroscopic determination of human meniscus composition.

This study investigates the correlation between the composition of human meniscus and its absorption spectrum in the visible (VIS) and near infrared (NIR) spectral range. Meniscus samples (n = 24) were obtained from nonarthritic knees of human cadavers with no history of joint diseases. Specimens (n = 72) were obtained from three distinct sections of the meniscus, namely; anterior, center, posterior. Absorption spectra were acquired from each specimen in the VIS and NIR spectral range (400–1,100 nm). Following spectroscopic probing, the specimens were subjected to biochemical analyses to determine the matrix composition, that is water, hydroxyproline, and uronic acid contents. Multivariate analytical techniques, including principal component analysis (PCA) and partial least squares (PLS) regression, were then used to investigate the correlation between the matrix composition and it spectral response. Our results indicate that the optical absorption of meniscus matrix is related to its composition, and this relationship is optimal in the NIR spectral range (750–1,100 nm). High correlations (R2uronic = 86.9%, R2water = 83.8%, R2hydroxyproline = 81.7%, p < 0.0001) were obtained between the spectral predicted and measured meniscus composition, thus suggesting that spectral data in the NIR range can be utilized for estimating the matrix composition of human meniscus. In conclusion, optical spectroscopy, particularly in the NIR spectral range, is a potential method for evaluating the composition of human meniscus. This presents a promising technique for rapid and nondestructive evaluation of meniscus integrity in real‐time during arthroscopic surgery.

Optical spectroscopic characterization of human meniscus biomechanical properties

Abstract. This study investigates the capacity of optical spectroscopy in the visible (VIS) and near-infrared (NIR) spectral ranges for estimating the biomechanical properties of human meniscus. Seventy-two samples obtained from the anterior, central, and posterior locations of the medial and lateral menisci of 12 human cadaver joints were used. The samples were subjected to mechanical indentation, then traditional biomechanical parameters (equilibrium and dynamic moduli) were calculated. In addition, strain-dependent fibril network modulus and permeability strain-dependency coefficient were determined via finite-element modeling. Subsequently, absorption spectra were acquired from each location in the VIS (400 to 750 nm) and NIR (750 to 1100 nm) spectral ranges. Partial least squares regression, combined with spectral preprocessing and transformation, was then used to investigate the relationship between the biomechanical properties and spectral response. The NIR spectral region was observed to be optimal for model development (83.0%≤R2≤90.8%). The percentage error of the models are: Eeq (7.1%), Edyn (9.6%), Eϵ (8.4%), and Mk (8.9%). Thus, we conclude that optical spectroscopy in the NIR range is a potential method for rapid and nondestructive evaluation of human meniscus functional integrity and health in real time during arthroscopic surgery.

Estimation of Systematic and Spatially Correlated Components of Random Signals from Repeated Measurements: Application to Contrast Enhanced Computer Tomography Measurements

Observational errors can be categorized into two groups: random noise, which is altered every time when measurement is repeated, and a systematic temporally invariant error. In this paper, we propose a method to estimate the covariance structure for systematic error and random noise using a small number of repeated measurements of the signal. We model the systematic and random components as stationary Gaussian random fields and use the Bayesian approach to estimate the spatial covariance functions of these components simultaneously. The study is motivated by an application related to the diagnosis of joint diseases using contrast enhanced computer tomography (CT) measurements. The noise in the measured contrast agent concentration profiles within cartilage tissue is strongly spatially correlated and includes a systematic component. Since the estimates are significantly sensitive to all errors in modeling, the systematic error and random noise components should be characterized for reliable estimation. The...