Modic changes in vertebral endplates: a comparison of MR imaging and multislice CT

OBJECTIVE

This paper aims to evaluate the presence of endplate sclerosis in different types of Modic changes and to assess the capability of MRI in detecting endplate sclerosis within these changes.

MATERIALS AND METHODS

The lumbar spines (L3-S1) of 70 patients were retrospectively reviewed to determine Modic changes and disc degeneration from MRI and endplate sclerosis from CT. T1- and T2-weighted signal intensity and Hounsfield unit (HU) measurements of type I and II Modic changes were recorded and the association of both Modic types I and II with endplate sclerosis was analyzed with a Mann-Whitney test.

RESULTS

Altogether 82 Modic changes in 36 subjects were recorded: 13% were type I, 12% mixed type I/II, 65% type II, 9% mixed type II/III, and 1% type III. Thirty-eight percent of the endplates with Modic changes had sclerosis in CT. Of specific Modic types, mixed I/II and II/III associated significantly with endplate sclerosis. Endplate sclerosis was not detected in MRI in a quantitative analysis.

CONCLUSION

Endplate sclerosis exists in all types of Modic changes, especially in mixed Modic types, and not only in type III changes, as previously assumed. Endplate sclerosis was not detected in MRI, which may depend on the amount of mineralization of the bone marrow.

Indentation diagnostics of cartilage degeneration

OBJECTIVE

Mechanical indentation and ultrasound (US) indentation instruments have been introduced for quantitative assessment of cartilage properties in vivo. In this study, we compared capabilities of these instruments to determine properties of healthy and spontaneously degenerated human patellar cartilage in situ and to diagnose the early stages of osteoarthritis (OA).

DESIGN

Six anatomical sites were localized from human patellae (N=14). By determining the force by which the tissue resists constant deformation (F(IND)), a mechanical indentation instrument was used to measure the compressive dynamic stiffness of cartilage. Further, the dynamic modulus (E(US)) and the US reflection coefficient of cartilage surface (R(US)) were measured with an US indentation instrument. For reference, Young's modulus and dynamic modulus were determined from cartilage disks using unconfined compression geometry. Proteoglycan and collagen contents of samples were analyzed microscopically. The samples were divided into three categories (healthy, early degeneration, and advanced degeneration) based on the Osteoarthritis Research Society International (OARSI) OA-grading.

RESULTS

Parameters R(US), E(US) and F(IND) were significantly associated with the histological, compositional and mechanical properties of cartilage (|r|=0.28-0.72, n=73-75, P<0.05). Particularly, R(US) was able to discern degeneration of the samples with high sensitivity (0.77) and specificity (0.98). All parameters, except R(US,) showed statistically significant site-dependent variation in healthy cartilage.

CONCLUSIONS

US reflection measurement shows potential for diagnostics of early OA as no site-matched reference values are needed. In addition, the high linear correlations between indentation and reference measurements suggest that these arthroscopic indentation instruments can be used for quantitative evaluation of cartilage mechanical properties, e.g., after cartilage repair surgery.

T2, Carr-Purcell T2 and T1rho of fat and water as surrogate markers of trabecular bone structure

Magnetic resonance imaging (MRI) techniques have been developed for non-invasive assessment of the structural properties of trabecular bone. These measurements, however, suffer from relatively long acquisition times and low resolution compared to the trabecular size. Spectroscopic measurement of relaxation times could be applied for more detailed and faster assessment of relaxation properties of bone marrow and also provide surrogate information on trabecular structure. In the present study, bovine trabecular bone was investigated with spectroscopic NMR (nuclear magnetic resonance) methods to determine the relationship between structural parameters as measured with micro-CT and T(2), Carr-Purcell T(2) and T(1rho) relaxation times of fat and water. To compare bone with a sample matrix with magnetic susceptibility interfaces, phantoms consisting of glass beads with different diameters in oil or water were used. The behavior of T(2) measured with different sequences and T(1rho) at different magnitudes of spin-lock fields were characterized, and relaxation times were correlated with structural parameters. T(2) and T(1rho) showed significant associations with structural bone parameters. Strongest linear correlations (r = 0.81, p < 0.01) were established between R(1rho) (1/T(1rho)) of fat component and structural model index. For glass beads, the behavior of T(2) and T(1rho) was similar to that of the water compartment of bone marrow. The present results suggest feasibility of spectroscopic NMR measurements to assess trabecular structure. However, further studies are required to determine the sensitivity of this approach to fat content of bone marrow and to lower the field strengths used in clinical devices.

Quantitative MRI of parallel changes of articular cartilage and underlying trabecular bone in degeneration

OBJECTIVE

To determine the interrelations between degenerative changes in articular cartilage and underlying trabecular bone during development of osteoarthritis and to test the ability of quantitative magnetic resonance imaging (MRI) to detect those changes.

METHODS

Human cadaver patellae were investigated with quantitative MRI methods, T(2) and dGEMRIC, at 1.5T. Same measurements for isolated cartilage samples were performed at 9.4T. Bone samples, taken at sites matched with cartilage analyses, were measured with MRI and peripheral quantitative computed tomography (pQCT). Mechanical and quantitative microscopic methods were also utilized for both cartilage and bone samples.

RESULTS

Significant differences were found between the samples with different stages of degeneration in mechanical properties, T(2) at 1.5T and proteoglycan (PG) content of articular cartilage. dGEMRIC at 9.4T discerned samples with advanced degeneration from the others. Bone variables measured with pQCT discerned samples with no or minimal and advanced degeneration, and mechanical properties of trabecular bone discerned samples with no or minimal degeneration from the others. Significant linear correlations were found between the bone and cartilage parameters. Characteristically, associations between variables were stronger within the samples with no or minimal degeneration compared to all samples.

CONCLUSIONS

Quantitative MRI variables, especially T(2) relaxation time of articular cartilage, may be feasible surrogate markers for early and advanced osteoarthritic changes in joint tissues, including decreased elastic moduli, PG and collagen contents of cartilage and mineral density and volume fraction of trabecular bone. Further work is required to resolve the relaxation mechanisms at clinically applicable field strengths.

Prediction of mechanical properties of trabecular bone using quantitative MRI

Techniques for quantitative magnetic resonance imaging (MRI) have been developed for non-invasive estimation of the mineral density and structure of trabecular bone. The R*(2) relaxation rate (i.e. 1/T*(2)) is sensitive to bone mineral density (BMD) via susceptibility differences between trabeculae and bone marrow, and by binarizing MRI images, structural variables, such as apparent bone volume fraction, can be assessed. In the present study, trabecular bone samples of human patellae were investigated in vitro at 1.5 T to determine the ability of MRI-derived variables (R*(2) and bone volume fraction) to predict the mechanical properties (Young's modulus, yield stress and ultimate strength). Further, the MRI variables were correlated with reference measurements of volumetric BMD and bone area fraction as determined with a clinical pQCT system. The MRI variables correlated significantly (p < 0.01) with the mechanical variables (r = 0.32-0.46), BMD (r = 0.56) and bone structure (r = 0.51). A combination of R*(2) and MRI-derived bone volume fraction further improved the prediction of yield stress and ultimate strength. Although pQCT showed a trend towards better prediction of the mechanical properties, current results demonstrate the feasibility of combined MR imaging of marrow susceptibility and bone volume fraction in predicting the mechanical strength of trabecular bone and bone mineral density.

T2 relaxation time and delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) of human patellar cartilage at 1.5 T and 9.4 T: Relationships with tissue mechanical properties

Quantitative magnetic resonance imaging (MRI) techniques have been developed for noninvasive assessment of the structure of articular cartilage. T2 relaxation time is sensitive to the integrity and orientation of the collagen network, while T1 relaxation time in presence of Gd-DTPA2- (dGEMRIC) reflects the proteoglycan content of cartilage. In the present study, human patellar cartilage samples were investigated in vitro to determine the ability of MRI parameters to reveal topographical variations and to predict mechanical properties of cartilage at two different field strengths. T2 and dGEMRIC measurements at 1.5 T and 9.4 T were correlated with the static and dynamic compressive moduli at six anatomical locations of the patellar surface. Statistically significant linear correlations were observed between MRI and mechanical parameters at both field strengths, especially between T2 and Young's modulus. No significant difference was found between the T2 measurements at different field strengths in predicting mechanical properties of the tissue. Topographical variation of T2 values at both field strengths was similar to that of Young's moduli. The current results demonstrate the feasibility of quantitative MRI, particularly T2 mapping, to reflect the mechanical properties of human patellar cartilage at both field strengths.

Cellulose sponge as a scaffold for cartilage tissue engineering

One goal of functional tissue engineering is to manufacture scaffolds infiltrated with chondrocytes which are suitable for transplantation into the lesion areas of articular cartilage. Various research strategies are used to fabricate cartilage transplants which would have the correct phenotype, contain enough extracellular matrix components, and have structural and biomechanical properties equivalent to normal articular cartilage. We have investigated the suitability of viscose cellulose sponges as a scaffold for cartilage tissue engineering. The sponges were tested alone, or with recombinant human type II collagen cross-linked inside the material. Scanning electron microscopy and confocal microscopy were used to study the structure of the scaffold during four weeks of cultivation. Cellulose and cellulose/recombinant type II collagen sponges were biocompatible for at least four weeks in cultivation, and gradual filling of the scaffold was observed. However, the constructs remained soft during the observation period, and were devoid of extracellular matrix composition typical for normal articular cartilage.