Another step towards the understanding of the earliest stages of osteoarthritis

Electrostatic interactions are important for the distribution of Gd(DTPA)(2-) in articular cartilage

PURPOSE

The delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) method can be used to assess the content of glycosaminoglycan in cartilage. In in vitro and model studies, the content of glycosaminoglycan is often expressed in terms of a fixed charge density (FCD). Values of the fixed charge density obtained using the dGEMRIC method differs from values obtained using other methods. The purpose of this work was to further clarify the origin of this discrepancy.

METHODS

dGEMRIC experiments were performed in a μMRI setup on a custom-designed, well-defined model system capturing the relevant ionic features of cartilage. The model system allows for good control over and systematic variation of relevant parameters. The experimental data was compared with results from Monte Carlo simulations on a coarse-grained model.

RESULTS

Application of ideal Donnan theory on data obtained from experiments as well as simulations lead to underestimation of the fixed charge density, in agreement with previous studies.

CONCLUSION

To obtain more accurate estimates of the fixed charge density using the dGEMRIC method, interionic interactions need to be taken into account in the Donnan analysis. Furthermore, the results suggest that the combination of μMRI dGEMRIC experiments and Monte Carlo simulations are useful tools for an improved understanding of these effects. Magn Reson Med 76:500-509, 2016. © 2015 Wiley Periodicals, Inc.

Magnetic resonance imaging and histology of ovine hip joint cartilage in two age populations: a sheep model with assumed healthy cartilage

OBJECTIVE

To compare morphologically normal appearing cartilage in two age groups with delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) and correlate magnetic resonance imaging (MRI) findings with histology.

MATERIALS AND METHODS

Twenty femoral head specimens collected from ten lambs (group I) and ten young adult sheep (group II) underwent dGEMRIC and histological assessment. A region of 2 cm(2) with morphologically normal-appearing cartilage was marked with a surgical suture for subsequent matching of MRI and histological sections. The MRI protocol included a three-dimensional (3D) double-echo steady-state sequence for morphological cartilage assessment, a B1 pre-scan with various flip angles for B1 field heterogeneity correction, and 3D volumetric interpolated breathhold examination for T1(Gd) mapping (dGEMRIC). Histological analysis was performed according to the Mankin scoring system.

RESULTS

A total of 303 regions of interest (ROI; 101 MRI reformats matching 101 histological sections) was assessed. Twenty-six ROIs were excluded owing to morphologically apparent cartilage damage or insufficient MR image quality. Therefore, 277 ROIs were analyzed. Histological analyses revealed distinct degenerative changes in various cartilage samples of group II (young adult sheep). Corresponding T1(Gd) values were significantly lower in the group of sheep (mean T1(Gd) = 540.4 ms) compared with the group of lambs (mean T1(Gd) = 623.6 ms; p < 0.001).

CONCLUSIONS

Although morphologically normal, distinct cartilage degeneration may be present in young adult sheep cartilage. dGEMRIC can reveal these changes and may be a tool for the assessment of early cartilage degeneration.

The evolution of articular cartilage imaging and its impact on clinical practice

Over the past four decades, articular cartilage imaging has developed rapidly. Imaging now plays a critical role not only in clinical practice and therapeutic decisions but also in the basic research probing our understanding of cartilage physiology and biomechanics.